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02 STS burning oil!


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My FIL has an 02 STS with only 16,000 miles on it. It's mainained regularly by the dealer, but is driven only a short commute on weekdays. The "check oil" message came on last week, it was 2 quarts low!! So he put some oil in it, and drove it to the dealer.

The dealer gave it a "top end flush", whatever that is, but wants to see the car again if it continues to drink oil. They're talking about rebuilding the motor!!

Has anyone ever heard of anything like this? Possible causes? Cures?

95 Eldo---Sold!

05 STS4-WooHoo!!!!!

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My FIL has an 02 STS with only 16,000 miles on it. It's mainained regularly by the dealer, but is driven only a short commute on weekdays. The "check oil" message came on last week, it was 2 quarts low!! So he put some oil in it, and drove it to the dealer.

The dealer gave it a "top end flush", whatever that is, but wants to see the car again if it continues to drink oil. They're talking about rebuilding the motor!!

Has anyone ever heard of anything like this? Possible causes? Cures?

Several clues here.

"2002 with 16,00 miles".

"Short commute".

That engine is loaded up with carbon (big time).

Take it on the Interstate and run it wide-open-throttle (WOT) in 2nd gear.

Leave the gear selector in "2" and WOT accelerate to the Colorado speed limit (75 MPH?) and then let the engine compression brake the car down to around 40 MPH. Repeat, repeat, repeat.

Ten rep's should produce a noticeable difference in oil consumption and performance.

The "check oil level" message is a good thing, BTW.

Jim

Drive your car.

Use your cell phone.

CHOOSE ONE !

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Everyone has heard of it. It is normal. Here is what out resident expert (a GM power train engineer) has to say about it.

"Northstar Oil Consumption

It is not unusual for a Northstar to use more oil than some other engines. It is a high performance engine and has to allow a little more oil to the top rings for lube as as well as down the 32 valve guides.

Design intent for oil consumption would put the engine at about 4000 miles per quart consumption but due to the variables in production parameters there are engines that will use 1 quart per 1000-1500 miles.... perfectly normal and acceptable... but more oil consumption than "intended". Nothing will be wrong with the engine but the continuous oil adds are aggravating. If this is the case then understand that the engine is probably going to run a long long time like that as the cylinder walls , rings, valve guides, etc. like all that oil that you are putting in and the continuous oil adds fortify the used oil in the sump and replenish the additive package in the oil that is slowly depleted under normal usage.

Comparing the 4.9 to the Northstar is an apples to oranges deal. The 4.9 is an excellent engine for it's purpose but does not offer nearly the performance, durability, fuel economy and emission control capability of the Northstar. The Northstar is a high output engine and likes to be "used".

The best way to minimize oil consumption in a Northstar is to keep the sump filled slightly low (many are continuously overfilled) by only checking the oil level when hot and only filling the sump with 7 quarts of oil (7.5 with a dry filter at a change.) A typical 8 quart fill at a change is "required" to put the oil level on the full mark when cold but is actually overfilling the crankcase promoting oil consumption.

Use conventional mineral oil (synthetic is not required at all) as it tends to provide better oil consumption.

An last, but not least, air the engine out frequently. It likes to be used and red-line upshifts at WOT help promote clean combustion chambers, exercise the piston rings to keep them free of carbon buildup and keep them mobile and to ensure the engine is broken in and maximum sealing is obtained. The Northstar does not like to be babied around. It likes to be run hard frequently with a WOT blast in merging or whatever.... Even engines reported to use 1 quart per 1500 miles tend to improve to 2500 miles per quart or better when subjected to a regular schedule of use and "abuse"...

----------

The subject of oil consumption really does not have a "final" answer. The fact is that there is some variability in oil consumption in all production engines.... regardless of who makes them on which continent. All the manufacturers recognize this and virtually all of them will call oil consumption as great as 1 quart in 1000 miles "normal" "acceptable" "allowable" "within production tolerances" etc... This doesn't mean that all engines will get 1000 MPQ or that the engine was designed to get 1000 MPQ...it just recognizes the fact that there are going to be some engines that get 1000 MPQ that will be perfectly fine upon disassembly and will have nothing "wrong" with them.

The variables that usually enter into oil consumption are primarily associated with the piston/ring/cylinder bore. The number of valves or type of valve actuation has little to do with it.

The single biggest variable and the one that has been discussed at great length on this forum is the cylinder bore finish or the cylinder honing pattern. The higher performance the engine is the more attention must be paid to the honing pattern and retention of oil on the cylinder walls to lubricate the piston and rings at full load , high RPM operation. The Northstar engine uses a very aggressive cylinder bore finish that tends to retain a lot of oil to protect the piston and rings. When the blocks are honed at the factory there is a tolerance in the bore finish due to the fact that the honing stones will wear and need replacement. A brand new stone gives a slightly more aggressive pattern than a "used" stone....so a block honed with new stones will have a more aggressive finish and most likely will use more oil.

Another variable is bore roundness. Like it or not, the bores tend to "move" slightly as the engine heats up and cools down and bolt tensions relax, etc. over time. All this contributes to slight bore out of roundness that is not bad or good...just different.

Carbon buildup in the rings and ring sealing are also variables that come into play with break in, operating schedule, type of oil used, etc.

The one thing that I can attest to is that many, many customer oil consumption complaint engines have been torn down with absolutely nothing wrong found. The engines are often reassembled and put into test cars and driven by the engineers and more often than not the high oil consumption does not repeat itself !!! The single biggest common cause seems to be breakin...or lack there of. Many, many oil consuming NOrthstar engines are "fixed" by some full throttle operation. I often joke about "driving it like you stole it" but it really is no joke. The Northstar engine was designed as a high performance engine to be run hard and fast. Those that are run hard typically exhibit excellent ring seal, little carbon build up and good oil economy. We have seen engines with tens of thousands of miles on them that the rings have not sealed or mated to the sides of the ring grooves because the operating schedule was so light duty. The moral here is to flog it .... often.

In any case, the nice thing about the engines with the more aggressive honing pattern is that the pistons, rings and bores will last forever. It is very common to tear down a 200,000 mile Northstar engine and still see the original honing pattern in the cylinders. There is never any sign of cylinder wall wear and the idea of a wear "ridge" at the top of the cylinder bore is something that is laughable on a Northstar.

The other nice thing about a little oil consumption is that it adds tremendous safety factor to the oil change interval. Nothing could be better for the engine than an occasional quart of fresh oil. You can take the worst oil on the market and add a fresh quart every 1000 miles and over the life of the engine the wear will be better than an engine run on the best oil with no adds between changes.

While no one in the engineering community wants high oil consumption the fact is that there is some variability in the oil consumption of an engine manufactured at the rate of 1200 per day. The specs of what is "normal" simply reflects this...it does not imply that all engines would get this or that something is wrong with and engine that gets more or less oil consumption.

There have been a lot of engineering changes over the years on the Northstar aimed at reducing the overall oil consumption and reducing the variability in the oil consumption of different engines. Many changes have been made to the honing process to make it more consistent. Changes to the piston and ring groove treatment have been made to make it more resistant to wear, pound out and micro welding at low oil retention rates. Regardless, there is still some variability.

One other thing that affects oil consumption, or the customers perception of oil consumption, is the move toward longer and longer change intervals. With the allowable change interval reaching as high as 12,500 miles on a 2003 Northstar if the oil life monitor is followed this could mean the addition of 3,4 or 5 quarts of oil to a very healthy engine. If the owner changes their oil every 2000 or 3000 miles, despite the oil life monitor recommendations, then they would not have to add any oil between changes. The oil consumption is the same....the amount added between changes is all that is different. Yet, many customers do not make the distinction. Field surveyors repeatedly show that "acceptable" oil consumption means "not having to add between changes"...whatever MPQ that is...???

The issue of oil consumption is very emotional , too, as many people perceive higher oil consumption as 'poor quality" or an indication that something is wrong. Blue smoke, fouling plugs, noise, etc...is a sign of something wrong. Using 1 quart in 1000 miles might be perfectly normal for an engine that has the high limit "rough" hone finish and is perfectly in spec...yet it will be perceived differently.

The Northstar engine in particular was designed to be a high performance engine and to perform well at high speeds and high loads. The engines are tested at loads and speeds for time periods few customers will ever be able to duplicate. It is unfortunate that the engineering that goes into making the engine capable of such running sometimes contributes to more oil consumption... especially as the production machining tolerances are taken into account.

The items mentioned about overfilling also apply. Make sure that the system is not overfilled as any excess oil will be pushed out the PCV. The best bet is to always check the oil hot and keep it midway between the add and full mark. Don't always top off and don't top off cold to the full mark as that will overfill the sump.

Hope this helps rather than adding more fuel to the fire... so to speak.

Incidentally, there is a lot in the message board / forum archives... check using "oil consumption" and read up. Always keep in mind that for every "oil burner" you read about on the internet there are 10,000 or more driving around perfectly fine that the people are not posting about... You are always going to read about the horror cases on the internet."

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Ranger that was just an awsome explanation on oil consumption on the N*. I found the detail on the quality of the N* engine just amazing. When I went to the morons that I made a mistake of letting do my engine swap, the first thing they said was " your lucky it is not a North Star". Still look at what I went through because of them. I now dream about owning an SLS with a N*. Maybe some day I will if I work hard enough. Till then can you post any info about my 1995 4.9L engine. I would love to know more about the quality or lack of with my new engine. Thanks a lot. Matt

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Matt,

Obviously that was Bbobynski's info about the Northstar that I cut and pasted. I don't want to take credit for that info.

The biggest "problem" with the Northstar seems to be head gaskets. I don't know how much of it comes from poor cooling system maintanence or a bad design, but they have definately gotten a bad rep whether deserved or not. Other than that I think it is one hell of an engine. Mine just turned 100K and so far so good.

I have never seen such a post from Guru regarding the 4.9. About the only "problem" I have ever heard of with it is the main bearing thump. Having said that, I had one for 125K and never experienced it or any other problems with it. I have heard it refered to as one of the best engines Cadillac ever made.

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Hi Ranger, hope you had a good Saturday. I did understand that you were posting info from the "resident expert (a GM power train engineer)". Tell ya what, I do not have a N* but I wish I did, maybe next time around. Maybe Guru will find time someday to post his openion about the 4.9. I put so much work into mine I'm kind of hopeing it's all worth it. I like what you said about it and what you have heard. Maybe I will have some good luck with mine as you did with yours. Thanks Ranger.

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