Oil Recommendations

[1RustyP]

Hi Folks,

I am new to this chat thingy so please bear with me. Just bought a 2003 Deville from a friend who had it out on a lease and was trading it in for new one. Very low mileage (his sife drove it most of the time) and price was definitely right. Always serviced at the dealer. My question is: What is the best oil to use in the Northstar. My Buick Regal GS (with supercharger) started and lived on Mobil One. It is still going strong with 76,000 miles and no maintenance to speak of. I have heard that Northstars are prone to use oil and that someone recommends against use of synthetics. Is this true.

Appreciate any replys as I have an oil change coming up soon and would like to put either Mobile One or Pennzoil Synthetic in it! Rusty

[Marika]

Hi Folks,

I am new to this chat thingy so please bear with me. Just bought a 2003 Deville from a friend who had it out on a lease and was trading it in for new one. Very low mileage (his sife drove it most of the time) and price was definitely right. Always serviced at the dealer. My question is: What is the best oil to use in the Northstar. My Buick Regal GS (with supercharger) started and lived on Mobil One. It is still going strong with 76,000 miles and no maintenance to speak of. I have heard that Northstars are prone to use oil and that someone recommends against use of synthetics. Is this true.

Appreciate any replys as I have an oil change coming up soon and would like to put either Mobile One or Pennzoil Synthetic in it! Rusty

At first when I saw your chat handle "Rusty" I thought perhaps you needed advise on oil because of a rusting problem.....

Anyway, if you search the archives of this site, you will find TONS of information.

Personally, I have the 4.9L engine and I use synthetic oil in it with no problems. Only the first time that I switched the car from regular to synthetic was there a little bit of seepage but that has since stopped.

I'll defer to the experts on this site to answer your question regarding the N* engine.

And by the way, welcome!

[1RustyP]

Actually that is my handle on the Mazda Tribute/Escape forum. I own a 2002 Tribby that is tricked out quite nicely. It is Chestnut Mica color which is Rusty mettalic. I just need some help with picking out what oil I want to put in the Caddy???

[Luke]

I personally use Mobil 1 synthetic. It works fine in the Northstar even though some on here say it is neither required nor recommended for the Northstar. I have had great luck with it and have never had any leaks because of it. Don't use the Pennzoil synthetic. It isn't a true synthetic. Mobil 1 is the only true synthetic that is readily available.

No maintenance has been required on the Regal GS? That's great! However, if you haven't had it done already, have the supercharger oil changed.

[CadiKing]

Welcome Rusty!

My advice: Use Mobil 1! I went to it after readng through the archives.

I Keep the oil filled to Half way up the bottom plastic bob on the end of

the dipstick, reading it ONLY from the backside after letting the hot engine

sit 20 minutes for complete drainage. Oil Change, 7.5 quarts, not 8 quarts

with filter. I burn maybe a half quart every 1200 miles! No big deal. Expect

up to a quart every 1000 miles due to the aggessive cylinder wall honng for

this superb high performance engine. Use the DIC to determine when to

change the oil. This way the oil, $3.81/qt @ Sams Club, and the Walmart filter

($1.97) prices will level out the cost of having sooo da*n much fun driving the car! Do not baby your new baby's gas peddle. It is prepared to give you WOT fun, over and over again. This car is a wolf in sheeps clothing! ENJOY!

If you don't mind hinting, how cheap did you get it? I am looking to add to my

single Caddy stable. I figure now is the time; gas prices are rising for the

summer. Many people would rather drive a gas saver. Myself, I prefer to Live

FREE in the United States of America with my Foot to the Floor as often as I can.

When the price of gas goes up more, there will be less people I have to pass in

the high speed lane with my WOT!

Oh, by the way, my reason for Mobil 1: In the unlikely event something would go wrong, and the engine would get too hot, the Mobil 1 will go beyond dino oils and

it will be worth it if it saves me from scorching the engine only once.

[Bob D]

Hi Folks,

I am new to this chat thingy so please bear with me. Just bought a 2003 Deville from a friend who had it out on a lease and was trading it in for new one. Very low mileage (his sife drove it most of the time) and price was definitely right. Always serviced at the dealer. My question is: What is the best oil to use in the Northstar. My Buick Regal GS (with supercharger) started and lived on Mobil One. It is still going strong with 76,000 miles and no maintenance to speak of. I have heard that Northstars are prone to use oil and that someone recommends against use of synthetics. Is this true.

Appreciate any replys as I have an oil change coming up soon and would like to put either Mobile One or Pennzoil Synthetic in it! Rusty

Hmmm..let me think about this..You know, why not use what the engineering team at the factory reccomended? I have this odd notion that they kinda thought it through before committing and putting in your manual.

[98deville]

i use castrol gtx

[JasonA]

Hmmm..let me think about this..You know, why not use what the engineering team at the factory reccomended? I have this odd notion that they kinda thought it through before committing and putting in your manual.

Hey, great point. In fact, I've been using what the factory recommends (10W-30 conventional oil, changed according to the oil life monitor) for 134,000 miles now. Car runs like new. We just got back from a 2100 mile trip and she ran beautifully. Only uses 1 quart between changes (at 5000-7000 miles).

[1RustyP]

CAdiKing,

I paid my friend @24,655 for the 2003 Deville with only 15,600 miles on the odometer. The leasing company was going to give him $25,000 trade on a new one. I know the maintenance was done by a dealer in the local area. Sounded to good to be true to me. My wife absolutely loves this car and I really like it on the highway. I am building a house down in North Carolina so we go back and forth a lot. Six hours one way but the Deville makes it feel like two or three. My Buick GS was great on the road but not like the Deville. Comfort and power all in one machine, great! I am looking to put Mobile One in at next oil change. Any recommendation on the weight, I guess 10W30 or ???

[1RustyP]

Jadcock,

I think we are going to be neighbors soon. Where in Sandhills are you??? I'm building at Beacon Ridge at Seven Lakes, West End, NC right outside Pinehurst!!!!!

[Bob D]

I put Mobile One in at next oil change. Any recommendation on the weight, I guess 10W30 or ???

Rusty, if you check the owners manual, I believe that you'll find the factory recommends what the engine started it's life with that year..5-30W

[JohnnyG]

Hmmm..let me think about this..You know, why not use what the engineering team at the factory reccomended? I have this odd notion that they kinda thought it through before committing and putting in your manual.

I am not convinced that the factory has considered all of the options when it comes to these "little things". There is some benefit to using a true synthetic oil in these engines, but you gotta get really technical about oil to understand. There have also been a lot of advances in oil manufacturing since the first Northstar rolled off the line. I'll try to give a general summary here, but I'm far from an expert.

Most synthetics are not synthetic at all, they are petroleum base stocks, chemically/physically modified to perform differently than the stuff that comes out of the ground. We all can thank Castrol for allowing them to be called synthetics in the first place, ever since they won the court battle with Mobil (1). So that is the first reason that the factory does not say using them is OK, there is too much variation in manufacturing processes.

Mobil1 is a true synthetic, it is what is generally known as a group IV or V synthetic. See this http://www.bobistheoilguy.com/oilbasics/ppframe.htm .

Mobil1 is not the ONLY synthetic, I don't know what all of them are, but there are more, like Redline, or Royal Purple, or Amsoil perhaps. Even Castrol makes a true synthetic these days, which I use in my Northstar.

Generally speaking, the main benefit to using a TRUE synthetic is the VI improver package. VI improvers are long chain polymers that break up when cold and recombine when hot, until they burn, then they make carbon, which sticks rings. These polymers is what puts the W in 10W-30. It allows the oil to act like an SAE 10 when its cold, and like an SAE 30 when hot. TRUE synthetics do not rely on VI improvers so much to provide this viscosity spread, they do it with the oil stocks themselves, and provide a lubricant that is more stable over a wide temperature range.

The Northstar is designed to provide outstanding longevity. One of the key ways to obtain this longevity is to provide outstand ring and cylinder life. The best way to achive this goal is to ensure that the rings and cylinders get PLENTY of oil, and never run dry. UNfortunately, a lot of other things now start to happen to screw things up. People see a dipstick in their shiney new Caddilac while it is sitting in the garage, they pull the dipstick out and the oil level is NOT at the FULL mark! Right away they rush out and get some oil and fill it up, never thinking to check the manual, which clearly states that the oil level should be checked HOT. This excess oil (and it's VI improvers) quickly gets burned off by the action of the pcv valve. It goes to the cylinders to get burned where it starts to stick the rings, and the cycle continues. To make matters worse, they figure thicker oil will slow down the now developing (or percieved) oil usage problem and go out and buy some 10W-50 with EVEN MORE VII's! It seems good at first, but gets much worse in a short time.

I use Castrol SLX 0W-30 (Made in Germany ONLY) in my Northstar. This appears to go against a lot of stuff I have just said, since it has a wide viscosity range, but it is a PAO or possibly a groupV oil with NO VII's. Further, when hot, it has a viscosity that is almost an SAE 40....not quite, but almost. It is an SL oil, but it does not get the GF-3 (fuel conserving) rating. MY Northstar is a 1999 with the flat tappets, it could use a little extra viscosity at temp. Most newer (post '99) engines have the roller tappets, and Mobil1 would be a better choice. Mobil1 tends to run a little thinner than most synthetics (but it gets the GF-3 starburst). The 0W-30 SLX still gets me 25 mpg on the highway, and a little better sometimes.

DO NOT check the oil level cold unless you keep it at the "ADD" mark on the stick or lower.

Hope this helps, if you need further info and have about a year to spend reading, go here: http://theoildrop.server101.com/ubb/ultimatebb.php

Your mileage will vary. Sorry for the long post.

[1RustyP]

Bob D.,

Great, I looked in the manual but didn't find that tidbit. Guess I looked in the wrong place. At least I know it will take 7.5 quarts with filter and I will buy Mobile One at Fort Meyer service station for $3.85 per quart. I have been using Purolator Pure One oil filters for my Buick GS and seem to be happy with them. I guess I'll use the same on the Caddy? Thanks for the input!

[KHE]

I wouldn't waste my money on the Mobil 1. It is good oil but the engine was validated using conventional oil. Use Texaco Havoline or Mobil Drive Clean oil were most likely the factory fill.

My '86 Park Avenue has 190,000 on the odometer and I have always used Valvoline or Shell conventional oil.

[Ranger]

When you ask about oil, you'll get more than you bargained for. Everyone has his/her favorite. My personal favorite is the one that's on sale. Have you ever heard of an engine oil related failure because of the BRAND of oil being used? Use what you feel good about, give it some tender loving WOT and it will serve you well for many years and miles.

[Luke]

Hmmm..let me think about this..You know, why not use what the engineering team at the factory reccomended? I have this odd notion that they kinda thought it through before committing and putting in your manual.

The smart *smurf* comments are not needed Bob D. Tell what kind of oil you prefer and leave it at that.

[1RustyP]

Larry,

I have always changed oil and filters on my cars and have gotten very concerned about what oil and filters I am using for a specific car and engine. My Buick Regal GS was first car I ever used exclusivly Mobile One and it sure has held up well. I think I will transfer that knowledge to my Caddy. Thanks

[Bob D]

Bob D.,

Great, I looked in the manual but didn't find that tidbit. Guess I looked in the wrong place. At least I know it will take 7.5 quarts with filter and I will buy Mobile One at Fort Meyer service station for $3.85 per quart. I have been using Purolator Pure One oil filters for my Buick GS and seem to be happy with them. I guess I'll use the same on the Caddy? Thanks for the input!

You bet, Rusty. As far as filters go most all of them out there are adequate, just stay away from Fram. If you're a purist like some of here, use AC Delco, the filter that the N* engine was validated with.

[rmac-etc]

QUOTE (Bob D @ May 26 2004, 02:28 PM)

Hmmm..let me think about this..You know, why not use what the engineering team at the factory reccomended? I have this odd notion that they kinda thought it through before committing and putting in your manual. 

The smart *smurf* comments are not needed Bob D. Tell what kind of oil you prefer and leave it at that.

That wasn't a smart *smurf* comment, its just a statement that a boutique oil, synthetic or otherwise is not needed. No one has ever shown (to my knowledge) that primo oil is of any benefit when changed according to the onboard recommendation. If it feels good to spend double, triple or more for oil then do it. Perhaps a bmw to wrap around it would be even better.

BobD keep it up!

(95 etc 137 k miles - rarely needs oil - wot's daily! ... oh btw, the cheapest name brand at the point of purchace should see me through for the next couple hundred thousand)

[CadiKing]

Comfort and power all in one machine, great! I am looking to put Mobile One in at next oil change. Any recommendation on the weight, I guess 10W30 or ???

Rusty,

I know what you mean about comfort & power. We do a lot of driving to Nascar races. I get into Virginia and the Carolinas from Ohio. Love to blow off people on the uphills @ 100 mph in West Virginia with the wife asleep in the seat next to me. I cannot wait for the next race everytime I pull in the drive from the last race!

I run 10w30 summer, 5w30 winter. Someone had suggested the Walmart filters because they worked at a facility that made them, along side Mobil 1 filters (cost $12.99). Now that you have got me thinking about it, I think I will switch over to

AC Delco, just to be safe. Why not support GM? I hate Walmart...they're ruining America...Don't get me started...Enjoy your wheels for many miles to come.

[KHE]

As far as filters go most all of them out there are adequate, just stay away from Fram. If you're a purist like some of here, use AC Delco, the filter that the N* engine was validated with.

Bob,

I've heard baaaaad things about Fram filters for years but wonder if they are really as bad as the internet sites, etc. say they are? Personally, I use AC Delco (or Purolator filters when the parts store is out of AC Delco).

[MAC]

Consumer Reports Article

The surprising truth about motor oils

July 1996, pp 10-13

Our 4-1/2-million-mile test with a fleet of New York City taxicabs turned some conventional wisdom on its head.

Mobil commercial claims its oil "has been in more Indy 500 winners than any other oil." Quaker State shows an engine with a terminally corroded inside what they imply could happen when you use another oil. Exxon's commercial for its Superflo oil urges motorists to "rely on the tiger."

Oil companies spend millions of advertising dollars each year to convince you that their oil can make your car's engine perform better and last longer. And purveyors of motor-oil and engine "treatments" assert that their products offer engine protection that oil alone can't provide. In our most ambitious test project ever, we set out to discover whether such claims are fact or fancy.

One way to gauge the performance of motor oils is to test them on the road. We did just that, using a fleet of 75 New York City taxicabs. Indeed, the oil industry itself tests its oils in New York City taxis.

For 22 months, we tested the performance of 20 popular motor oils. Each of those oils met the industry's latest standards, as certified by a starburst symbol on the container. (See "It's not just oil," article 3 of 4.) We also tested Slick 50 Engine Treatment and STP Engine and Oil Treatments.

In addition to the taxicab tests, we had the oils' chemical and physical properties analyzed by an independent lab. We also surveyed our subscribers about their oil-changing experiences and preferences, and we sent shoppers to quick-lube centers across the country to assess the service. Finally, because changing the oil is just one part of car care, we've reviewed some other ways you can help keep your car running longer. That report begins on page 18 (not included in this e-mail).

Testing the oils

We put identical rebuilt engines with precisely measured parts into the cabs at the beginning of the test, and we changed their oil every 6,000 miles. That's about twice as long as the automakers recommend for the severe service that taxicabs see, but we chose that interval to accelerate the test results and provide worst-case conditions. After 60,000 miles, we disassembled each engine and checked for wear and harmful deposits.

Our test conditions were grueling, to say the least. The typical Big Apple cab is driven day and night, in traffic that is legendary for its perversity, by cabbies who are just as legendary for their driving abandon.

When the cabs aren't on the go, they're typically standing at curbside with the engine idling - far tougher on motor oil than highway driving. What's more, the cabs accumulate lots of miles very quickly, making them ideal for our purposes. Big-city cabs don't see many cold start-ups or long periods of high speed driving in extreme heat. But our test results relate to the most common type of severe service - stop-and-go city driving.

Each of the 20 oils we studied was tested in three cabs to provide meaningful test results even if a few cabs fell out with mechanical problems or because of accidents. (Six of the 75 engines did, in fact, have problems, none apparently related to the oil's performance.) For a detailed description of our test procedures, see "Testing in the Big Apple," article 2 of 4.

Our shoppers all across the country bought hundreds of quart containers of oil. Some brands had slightly different formulations in different areas, but all the oils included a full package of additives.

The independent lab helped us identify the most representative formulations of each brand. Our engineers transferred containers of that oil to coded 55-gallon drums and hauled them to the fleet garage for testing.

Ideally, oil should be thin enough to flow easily when the engine is cold and remain thick enough to protect the engine when it's hot. The lab analyses of each oil's viscosity characteristics - its ability to flow-indicate that motor oils have improved since 1987, when we last tested them. This time, far fewer test samples failed to meet the viscosity standards for their grade - and those were typically outside the limits by only a slight amount. No brand stood out as having a significant problem.

We tested oils of the two most commonly recommended viscosity grades - 10W-30 and 5W-30. Automakers specify grades according to the temperature range expected over the oil-change period. The lower the number, the thinner the oil and the more easily it flows.

In 5W-30 oil, for example, the two numbers mean it's a "multiviscosity" or "multigrade" oil that's effective over a range of temperatures. The first number, 5, is an index that refers to how the oil flows at low temperatures. The second number, 30, refers to how it flows at high temperatures. The W designation means the oil can be used in winter.

A popular belief is that 5W-30 oils, despite their designation, are too thin to protect vital engine parts when they get hot. However, one of our laboratory tests measured the viscosity of oils under high-temperature, high-stress conditions and found essentially no difference between 5W-30 oils and their 10W-30 brand mates. But at low temperatures, the 5W-30 oil flowed more easily.

Viscosity grade is important, so be careful. Recommendations vary with the make, engine, and model year of the car, so check your owner's manual and ask the mechanic for the proper grade of oil.

Of the 20 oils we tested, nine were conventional 10W-30 oils, and eight were 5W-30. We also tested two synthetic oils, Mobil 1 and Pennzoil Performax, and one synthetic-and conventional blend, Valvoline DuraBlend; all three were 10W-30 oils.

No brand performed best

If you've been loyal to one brand, you may be surprised to learn that every oil we tested was good at doing what motor oil is supposed to do. More extensive tests, under other driving conditions, might have revealed minor differences. But thorough statistical analysis of our data showed no brand-not even the expensive synthetics-to be meaningfully better or worse in our tests.

After each engine ran about 60,000 miles (and through 10 months of seasonal changes), we disassembled it and measured the wear on the camshaft, valve lifters, and connecting-rod bearings. We used a tool precise to within 0.00001 inch to measure wear on the key surfaces of the camshaft, and a tool precise to within 0.0001 inch on the valve lifters. The combined wear for both parts averaged only 0.0026 inch, about the thickness of this magazine page. Generally, we noted as much variation between engines using the same oil as between those using different oils. Even the engines with the most wear didn't reach a level where we could detect operational problems.

We measured wear on connecting rod bearings by weighing them to the nearest 0.0001 gram. Wear on the key surface of each bearing averaged 0.240 gram - about the weight of seven staples. Again, all the tested oils provided adequate protection.

Our engineers also used industry methods to evaluate sludge and varnish deposits in the engine. Sludge is a mucky sediment that can prevent oil from circulating freely and make the engine run hotter. Varnish is a hard deposit that would remain on engine parts if you wiped off the sludge. It can make moving parts stick.

All the oils proved excellent at preventing sludge. At least part of the reason may be that sludge is more apt to form during cold startups and short trips, and the cabs were rarely out of service long enough for their engine to get cold. Even so, the accumulations in our engines were so light that we wouldn't expect sludge to be a problem with any of these oils under most conditions.

Variations in the buildup of varnish may have been due to differences in operating temperature and not to the oils. Some varnish deposits were heavy enough to lead to problems eventually, but no brand consistently produced more varnish than any other.

The bottom line. In our tests, brand didn't matter much as long as the oil carried the industry's starburst symbol (see "It's not just oil," article 3 of 4). Beware of oils without the starburst; they may lack the full complement of additives needed to keep modem engines running reliably.

One distinction: According to the laboratory tests, Mobil 1 and Pennzoil Performax synthetics flow exceptionally easily at low temperatures - a condition our taxi tests didn't simulate effectively. They also had the highest viscosity under high-temperature, high-stress conditions, when a thick oil protects the engine. Thus, these oils may be a good choice for hard driving in extreme temperatures.

Note, too, that a few automakers recommend specific brands of motor oil in the owner's manual. You may need to follow those recommendations to keep a new car in warranty.

Oil changes: How often?

The long-time mantra of auto mechanics has been to change your oil every 3000 miles. Most automakers recommend an oil change every 7,500 miles (and a specific time interval) for "normal" driving, and every 3,000 miles for "severe" driving - frequent trips of less than four or five miles, stop-and-go traffic, extended idling, towing a trailer, or dusty or extremely cold conditions. Many motorists' driving falls into one or more of those "severe" categories.

In our survey, almost two-thirds of our readers said they had their oil changed every 3,000 miles or less. They may be following the thinking expressed by one of our staffers: "I have my oil changed every 3,000 miles because that's what my father did, and all his cars lasted for many years."

To determine whether frequent oil changes really help, we changed the oil in three cabs every 3,000 miles, using Pennzoil 10W-30. After 60,000 miles, we compared those engines with the engines from our base tests of the same oil, changed every 6,000 miles. We saw no meaningful differences. When Mobil 1 synthetic oil came out, Mobil presented it as an oil that, while expensive, could go 25,000 miles between changes. That claim is no longer being made. But Mobil 1 is still on the market, selling at a premium (along with pricey synthetic competitors from several other companies). And synthetic oil's residual reputation as a long-lasting product may still prompt some people to stretch their oil changes longer than the automaker recommends.

Determining whether synthetic oils last longer than conventional ones would require a separate test protect. To try to get some indication, we put Mobil 1 synthetic into three cabs and changed their oil every 12,000 miles.

We intended to compare the results of these tests with those from the three taxicabs whose Mobil 1 was changed at our normal interval, every 6,000 miles. Unfortunately, two of the three engines using the 12,000-mile interval developed problems. (We couldn't attribute those problems to the oil.) The third engine fared no worse than the three whose oil had been changed at 6,000-mile intervals.

The bottom line. Modern motor oils needn't be changed as often as oils did years ago. More frequent oil changes won't hurt your car, but you could be spending money unnecessarily and adding to the nation's energy and oil-disposal problems.

Even in the severe driving conditions that a New York City taxi endures, we noted no benefit from changing the oil every 3,000 miles rather than every 6,000. If your driving falls into the "normal" service category, changing the oil every 7,500 miles (or at the automaker's suggested intervals) should certainly provide adequate protection. (We recommend changing the oil filter with each oil change.)

We don't recommend leaving any oil, synthetic or regular, in an engine for 12,000 miles, because accumulating contaminants - solids, acids, fuel, and water - could eventually harm the engine. What's more, stretching the oil-change interval may void the warranty on most new cars.

Testing Slick 50 and STP

We also tested Slick 50 and STP Engine Treatments and STP Oil Treatment, each in three cabs. (Slick 50 costs $17.79 per container; STP Engine Treatment has been discontinued.) All three boast that they reduce engine friction and wear.

The engine treatments are added with the oil (we used Pennzoil 10W-30). They claim they bond to engine parts and provide protection for 25,000 miles or more. We used each according to instructions.

The STP Oil Treatment is supposed to be added with each oil change. It comes in one formulation (black bottle, $4.32) for cars with up to 36,000 miles, another (blue bottle, $3.17) for cars that have more than 36,000 miles or are more than four years old. We used the first version for the first 36,000 miles, the second for the rest of the test-again, with Pennzoil 10W-30.

When we disassembled the engines and checked for wear and deposits, we found no discernible benefits from any of these products.

The bottom line. We see little reason why anyone using one of today's high-quality motor oils would need these engine/oil treatments. One notable effect of STP Oil Treatment was an increase in oil viscosity; it made our 10W-30 oil act more like a 15W-40, a grade not often recommended. In very cold weather, that might pose a risk of engine damage.

Recommendations

None of the tested oils proved better than the others in our tests. There may be small differences that our tests didn't reveal, but unless you typically drive under more severe conditions than a New York cab does, you won't go wrong if you shop strictly by price or availability. Buy the viscosity grade recommended in your owner's manual, and look for the starburst emblem. Even the expensive synthetics (typically, $3 or $4 a quart) worked no better than conventional motor oils in our taxi tests, but they're worth considering for extreme driving conditions high ambient temperatures and high engine load or very cold temperatures.

On the basis of our test results, we think that the commonly recommended 3,000-mile oil-change interval is conservative. For "normal" service, 7,500-mile intervals (or the recommendation in your owner's manual) should be fine. Change the oil at least that often to protect your engine and maintain your warranty. Even for the severe service experienced by the taxis in our tests a 6,000- mile interval was adequate. But some severe service - frequent cold starts and short trips, dusty conditions, trailer towing - may require a shorter interval. Note, too, that special engines such as diesels and turbos, which we didn't test, may need more frequent oil changes.

We don't recommend stretching the change interval beyond the automaker's recommendations, no matter what oil you use. Engine combustion contaminants could eventually build up and harm engine parts.

As for STP Oil Treatment, STP Engine Treatment, and Slick 50 Engine Treatment, our advice is simple: If you use an oil with the starburst symbol, you don't need them.

Testing in the Big Apple

New York City taxicabs played a key role in our massive test project to evaluate motor oils. For consistency, we used only 1992-93 Chevrolet Caprice cabs. Each received a precisely rebuilt 4.3-liter V6 at the beginning of its 60,000-mile test. We started with six rebuilt engines; after each engine was installed in a cab, the six engines that were removed were rebuilt and installed in six other cabs-and so on. Using that rotation, we monitored 75 cabs over 4-1/2 million miles of driving in New York City and its environs. Each oil was tested in three engines.

A local shop completely machined each engine block and crankshaft, rebuilt the cylinder heads, and installed new bearings, pistons, rings, seals, gaskets, and oil pump. Though the engines originally had roller lifters and camshafts, a design that reduces friction, we installed conventional sliding lifters and camshafts to accelerate wear.

Before the engines were assembled, we measured or weighed the parts most likely to show wear if the oil wasn't doing its job - the camshafts, valve lifters, and connecting-rod bearings. Each cab went through a break-in procedure before hitting the road. During testing, two engine timers measured the time the engine was running and the time it was in gear.

Over the next 22 months, our engineers paid more than 100 calls - usually without notice - on the fleet garage. They dropped off test oil and picked up used-oil samples for ongoing analysis. They also made sure that oil was being added to the engines when necessary and changed as scheduled.

After each 60,000-mile test, we remeasured the key engine parts. We also examined combustion-chamber deposits, the color of the valves, scoring of cylinder walls, and valve-deck deposits for any sign of engine problems.

It's not just oil

Certainly, motor oil is slippery. That's what helps protect an engine's moving parts. But motor oil does much more than lubricate. It helps cool the engine keep it clean, prevent corrosion, and reduce friction to improve fuel economy. To do all that, refiners blend in various additives, which account for 10 to 25 percent of the product you buy.

The oil industry has devised a starburst symbol (described at the bottom of this article) to certify that a particular motor oil meets the latest industry requirements for protection against deposits, wear, oxidation, and corrosion. The starburst on the label means the oil meets API (American Petroleum Institute) Service SH requirements - the latest, most advanced formulation. (Service SH supplants SG, the previous top category.) The CD designation on most of the oils we tested refers to diesel performance. The starburst also indicates that the oil passes ILSAC/GF-1 standards developed by the International Lubricant Standardization and Approval Committee, a U.S.-Japanese group. And it means the oil meets Energy Conserving II requirements - it improves fuel economy by reducing engine friction. All the oils we tested carry the starburst - and all performed well in our tests. But note that oils without that symbol may not perform as well.

Below are some of the additives found in modern oils.

Viscosity-index improvers modify the oil so its viscosity is more consistent over a wide temperature range.

Antioxidants prevent the oil from thickening when it runs hot for extended periods.

Dispersants keep contaminants suspended so they don't form deposits in engine.

Detergents help prevent varnish and sludge on engine parts and neutralize acid formed in engine.

Rust and corrosion inhibitors protect metal parts from acids and water formed in engine.

Pour-point depressants help the oil flow in a cold engine, especially in cold weather.

Foam inhibitors collapse the bubbles churned up by engine crankshaft. (Foam reduces lubricating effectiveness.)

Friction modifiers strengthen the oil film and prevent unlubricated contact between moving parts.

Antiwear agents provide lubrication when oil is squeezed out from between moving engine parts.

The starburst symbol is a circle with a serrated edge about an inch across with text which reads "AMERICAN PETROLEUM INSTITUTE CERTIFIED FOR GASOLINE ENGINES."

Ratings & Recommendations Motor oils

Shopping strategy

Discount stores are generally the least expensive place to buy oil. Look for sales and buy by price - but make sure the container has the starburst symbol.

Details Listed alphabetically

All the tested oils performed well in our tests, and all claim to meet the latest (API-SH and ILSAC/GF-1) industry standards (see "It's not just oil," article 3 of 4). Prices are the average for one quart, based on a national survey of discount stores.

5W-30 oils

Castrol GTX $1.21

Appears to use same formulation in all areas sampled. Graduated container.

Exxon Superflo

Price not available; not widely found in discount stores. Appears to use same formulation in all areas sampled. Graduated container with window.

Fire & Ice All-Season (Shell) * $0.93

Different formulations in Florida and New York. Graduated container with window.

Havoline Formula 3 (Texaco) $1.11

Appears to use same formulation in all areas sampled. Graduated container with window.

Mobil * $0.95

Appears to use same formulation in all areas sampled. Graduated container with window.

Pennzoil $1.16

Appears to use same formulation in all areas sampled. Graduated container.

Quaker State Deluxe * $1.20

Appears to use same formulation in all areas sampled. Graduated container with window. 10W- 30 is called Super Blend.

Valvoline All-Climate $1.14

Different formulations in California and Texas. Graduated container with window.

10W-30 oils

Castrol GTX $1.18

Appears to use same formulation in all areas sampled. Graduated container.

Exxon Superflo $1.13

Different formulation in Florida. Graduated container with window.

Fire & Ice All-Season (Shell) * $0.99

Appears to use same formulation in all areas sampled. Graduated container with window.

Havoline Formula 3 (Texaco) * $1.13

Different formulations in Illinois and Texas. Graduated container with window.

Kendall Superb 100 * $$1.23

Different formulation in Florida. 5W-30 version not tested.

Mobil 1 synthetic $3.76

Low-temperature flow characteristics were better than most. Appears to use same formulation in all areas sampled. 5W-30 version not tested. Graduated container with window.

Mobil $0.95

Different formulation in New York. Graduated container with window.

Pennzoil $1.16

Appears to use same formulation in all areas sampled. Graduated container.

Pennzoil Performax synthetic $2.97

Low-temperature flow characteristics were better than most. No 5W30 version. Appears to use same formulation in all areas sampled.

Quaker State Super Blend * $1.20

Appears to use same formulation in all areas sampled. Graduated container with window. 5W-30 is called Deluxe.

Valvoline All-Climate $1.13

Different formulation in California. Graduated container with window.

Valvoline Semi-Synthetic DuraBlend Conventional/synthetic blend * $2.12

Appears to use same formulation in all areas sampled. Graduated container with window, No 5W-30 version. Flow characteristics were more like those of a conventional oil than those of a synthetic.

* One or more samples differed from viscosity-grade requirement by a small amount.

The table below shows price ranges of five popular 10W-30 oils in discount stores and auto-parts stores, on the basis of a national survey. Discount stores account for an estimated 51 percent of do-it-yourself oil sales; auto-parts stores, nearly 35 percent. Service stations tend to be the most expensive, charging as much as $2.50 a quart.

Castrol GTX

Discount Store $0.89-1.69

Retail Auto Parts Store $1.24-1.80

Havoline Formula 3

$1.08-1.39

$1.09-1.61

Pennzoil

$1.08-1.39

$1.24-1.89

Quaker State Super Blend

$1.06-1.69

$1.19-1.80

Valvoline All-Climate

$0.89-1.69

$1.22-1.99

[Bob D]

As far as filters go most all of them out there are adequate, just stay away from Fram.  If you're a purist like some of here, use AC Delco, the filter that the N* engine was validated with.

Bob,

I've heard baaaaad things about Fram filters for years but wonder if they are really as bad as the internet sites, etc. say they are? Personally, I use AC Delco (or Purolator filters when the parts store is out of AC Delco).

You know Kevin, I was a big Fram user (oil and air) for years. I had their stuff in all my cars, hotrods, high peformance rides, commuter cars, trucks, even tractors.

Somehere in the mid to late ninties, their oil filters dissapeared of the shelves in all the local auto parts stores...Hmm..I got around to asking the managers about this, and all they would say is that they were instructed to pull ALL Fram oil filters of the shelves, for an undetermined amount of time. Well, it turns out there was a class action suit going on against Fram for the alleged destruction to engines caused by their filters coming apart internally due to shoddy manufacturing.

Suddenly, Fram filters appeared on the shelves again after what seemed like 18 months or so. Huh, suit settled? Yes, out of court by arbitration I was told. I also heard that Fram started right up again where they left off...Since then, there has been internet reports of inferior Fram quality done in more than one study.

Bottom line for me is, although I wasn't there to witness any of this history, (except for the dissaperance off the shelves for awhile) it's enough to stay away from their stuff permanently. Why take the risk? There's plenty of proven good filters out there such as AC Delco (my first choice) and Purolator, that you mentioned.

[Bob D]

Consumer Reports Article

The surprising truth about motor oils

July 1996, pp 10-13

Dang Mac, in all the years I've been hanging around here, I do believe you get the "Longest Post" award! LOL (Bruce, is there such a thing?)

Interesting reading, I wonder what is specifically different in the individual states formualtions...

[Bob D]

I am not convinced that the factory has considered all of the options when it comes to these "little things".

LOL...LOL....LOL....LOL.....LOL.....Horse crap.....LOL.....LOL

BTW....take this as being tongue-in-cheek. Not wanting to cause a flamer here....LOL

But wait, there's more....my current ride, a 2005 Saturn ION Red Line with a supercharged 205 HP EcoTec 4 cylinder comes from the factory with .....ack.....SYNTHETIC oil....not even US spec synthetic but Elf brand, Euro spec 5W30 synthetic as the engine is built and hot tested in Germany..... How could THIS happen??? At 100 HP per liter it needs all the help it can get...LOL...LOL.... actually it has to do with the ring breakin and the supercharger and the fact that the other engines on that line get the synthetic oil also...they are turbo charged.

The smart *smurf* comments are not needed Guru . Tell what kind of oil you prefer and leave it at that.

I couldn't resist.