Oil Life Monitor Question

[Ohio Jim]

Hello everyone,

My '99 STS oil life monitor cycles roughly every 7,000 to 7,500 miles. I add a quart every 4,000 miles. All is good. My '04 Deville started at 22,000 miles and did not call for a change until 33,000 miles. I really did not think much of it until I was preparing for a 4,000 mile road trip to Florida with 50% on the OLM; 39,000 on the odometer. I planned to change the oil before I left so I would nor come up short in case we went much farther than planned. I watched the OLM during the trip, and was pleasently surprised to arrive home with 17% remaining. Is this normal? Seems like when I have checked the oil level after 2,000 or 3,000 miles, the oil still looked clean! Is the '04 Northstar that much better than the '99 engine? Or should I alter my oil change habits?

Thanks in advance for your replies,

Ohio Jim

[JimD]

Hello everyone,

My '99 STS oil life monitor cycles roughly every 7,000 to 7,500 miles. I add a quart every 4,000 miles. All is good. My '04 Deville started at 22,000 miles and did not call for a change until 33,000 miles. I really did not think much of it until I was preparing for a 4,000 mile road trip to Florida with 50% on the OLM; 39,000 on the odometer. I planned to change the oil before I left so I would nor come up short in case we went much farther than planned. I watched the OLM during the trip, and was pleasently surprised to arrive home with 17% remaining. Is this normal? Seems like when I have checked the oil level after 2,000 or 3,000 miles, the oil still looked clean! Is the '04 Northstar that much better than the '99 engine? Or should I alter my oil change habits?

Most of the difference in OLM calibration between the two engines can be explained by (1) the incorporation of roller cam followers in 2000 and (2) the difference in oil additive chemistry from 1999 to 2004. The OLM calibration/certification takes those variables and others into consideration.

Plus running an engine continuously at normal operating temperature for hours on end (Interstate operation) causes the OLM to count down at a slower rate (MUCH slower). Operating an engine for short periods without a complete warmup (urban/suburban operation) causes the OLM to count down at a faster rate.

You can trust the OLM; in fact there is a 100% safety factor built in to the algorithm.

My current GM daily driver is a 2011 model that specifies dexos1 motor oil. I have a spreadsheet setup that allows me to 'project' oil change mileage based on miles driven and current OLM percentage. During periods of urban/suburban driving, I observe a calculated 100 miles per OLM percent. After a 2,000 run on the Interstate system, I observe a calculated 140+ miles per OLM percent. I am unable to benefit from the longer oil change interval since I now drive less than 12,000 miles per year!

Don't change what you are doing. Your observations are normal and even to a point are predictable.

[Z15]

I have over a year and just over 10,000 miles on the oil change in my '09 CTS4 and the OLM is on its 2nd go round, its at 47% this am. I reset it to 100% the first time it hit 0 because I go 10,000 miles on an OCI with 100% Synthetic Oil.

Before you jump on me, be advised I been doing this since 1978 and the synthetic oil I use has never let me down. I have NEVER changed oil at less than 10,000 miles (even went as high as 25,000 miles in the past when I was driving more) unless it was to get rid of the low-bidder oem oil that came in the vehicle. My vehicles do not use any oil ever...

2009 CTS4 3.6L Sedan

2012 Sierra Denali AWD 6.2L

[Göran W]

I´ll start the jumping.......

[cdgrinci]

I still think the 'hot plan' is to change (as per the owners manual), at the advise of the OLM or one year (whichever comes first).

[Cadillac Jim]

I recall an old post that quoted an even older post by the "guru" that said that the OLM works using engine revolutions and coolant temperature. If you run along at 2200 RPM at normal operating temperature in 4th gear with the TCC engaged, this can roll off the miles without using up the oil additives and the OLM is calibrated for this.

[Z15]

fyi

Oil Life Monitor -- How Does It Know?

How long will oil last in an engine? What reduces the oil’s effectiveness? When should it be changed?

Lubrication engineers perform a number of tests to answer these kinds of questions. Vehicles are operated under prescribed conditions, and periodically a sample of the oil is taken into the laboratory for analysis. When the condition of the oil is no longer satisfactory, the mileage is noted. From controlled testing like this, engineers in the past have determined two sets of mileage numbers, one number for normal driving and the other for severe conditions. Severe conditions can mean that the vehicle is driven hot (for example, pulling a trailer up a mountain) or is driven such that the oil never warms completely (for example, trips less than 5 or 10 miles in a winter climate). It is then up to the owner to decide whether their own driving is normal or severe and to change the oil accordingly. Now, science and technology have found a way of taking the guesswork out of the picture. GM is installing an oil life monitor in an increasing number of new vehicles. Using a simple indicator lamp or readout on the instrument panel, this system notifies the driver when to change the oil. The February and March 2000 issues of TechLink explain how to reset these monitors.

Here’s information on how an oil life monitor works.

Additives

Straight oil is not an ideal lubricant in an engine. A package of additives is needed to give the oil properties it does not naturally have or to enhance its natural properties. Some of the tasks accomplished by additives:

- viscosity modifiers, to keep the oil the proper thickness over a wide range of operating temperatures

- anti-oxidant, to keep the oil from thickening

- corrosion inhibitors, to protect engine components

- anti-wear

- anti-foam

- detergents, to suspend solid particles.

What Makes Oil "Wear Out?"

If you were to start out with a crankcase full of fresh, clean oil, and drove the vehicle for a period of time, eventually the oil would have to be changed. During this time, what can change fresh oil into "worn out" oil?

First, dilution. When gasoline is burned in the combustion chamber, the by-products include a lot of water. Some of this water can find its way into the crankcase through piston ring blow-by. If the engine is cold, and if combustion is not perfectly complete, a small amount of acid is formed. It, too, can blow-by into the oil. You don’t need to be a top-notch scientist to realize that water and acid aren’t good things to pump through the lubrication system of the engine. If an engine is run long enough for the engine oil to warm, the water and acids will evaporate and not accumulate. But, during very short trips in cold weather, water and acids can enter the engine oil and cause the oil to "wear out." Second, the degradation of the oil and its additives. We mentioned earlier that a number of additives are put into oil to improve its performance. If these additives are degraded or decomposed, the oil is no longer capable of doing all of its jobs properly. Oil with degraded additives can become thick and dark. Additives become degraded by exposure to extreme heat. There are two places a lot of heat can reach the oil. One is near the combustion chamber. Oil at the top piston ring is exposed to very high temperature. And some bearing surfaces can also put a lot of heat into the oil at high operating temperatures. So, degradation of additives from high temperature operation is the second factor that can cause oil to "wear out."

How Can Operating Conditions be Used to Predict Oil Life?

Using carefully controlled laboratory tests, it’s possible for lubrication engineers to measure how long it takes to dilute engine oil during cold operation. And it’s possible to measure how long it takes for high temperature to degrade the additives. We usually think of measuring time in hours and minutes, but for an engine, the

amount of revolutions it has run is also a good measure. So for the purposes of oil life, time is measured in engine revolutions. Engineers like to talk in terms of models. A model is a way to describe something mathematically. It’s possible to create an oil life model that very carefully matches the results of analyzing the oil in a laboratory.

The oil life monitor, then, is based on a model. A computer chip in the Powertrain Control Module is loaded with a certain number of engine revolution counts. The count for each engine/vehicle combination is determined by testing. As the engine runs, each revolution is subtracted from the remaining count in the oil life monitor. When the count reaches zero, the instrument panel light comes on. But, here’s the clever part. When the various input sensors detect that the engine is running under either cold or hot conditions, it subtracts extra counts (penalties) for each engine revolution. So, the conditions that cause the oil to "wear out" make the counter run down faster. When the oil is changed, it’s necessary to reset the oil life monitor (see the February and March 2000 issues of TechLink) and the countdown begins again.

NOTE: Synthetic oil resists "wearing out" better than mineral oil, so the oil life monitor

is set to account for this, but only on vehicles that are specified for synthetic oil from the

factory -- the Corvette, for instance. Using synthetic oil in other vehicles is certainly not

harmful, but the oil life monitor will continue to count down as though the engine contained

mineral oil.

- Shirley Schwartz contributed to this article

Note - Dr. Shirley Schwartz is the GM engineer who invented it.

http://www.nae.edu/30433.aspx

[Ohio Jim]

Man, you guys are the best! Thank you for all the replies and information contained there-in. It seemed as though I might be running that oil too long, but now I am absolutely sure to go with what I am doing. I will from this day forward, always trust in the OLM, without question! Scout’s honor! Lol Just one more reason why I love Cadillacs!

Sincerely,

Ohio Jim

[rockfangd]

I go strictly by the OLM except for when I first purchase the vehicle, and if something is done.

on my 96 Deville, DD, shorter trips, less trips. I have to change the oil more and has higher consumption

My 97 Seville is usually only long trips, I have gone 3500 miles this year and have had to add no oil, and still have 65% OLM.

I remember My olds cutlass supreme had a DIS (driver info system) and it was very accurate also

[Cadillac Jim]

I once went by the odometer, 3,000 to 4,000 miles, and the smell of the oil on the dipstick. Good engines that incorporate good crankcase breathing like the Northstar don't put much blowby in the oil so the smell isn't worth much, but the color may be helpful. In any case, once I got better educated on the OLM and such I started changing my oil at the 40% to 50% mark on the OLM.

I also use nothing but synthetic oil, a habit I got when I got my 1990 Pontiac Gran Am Quad 4 HO, which recommended 5W-30 with Mobil 1 suggested as a premium upgrade. Those little high-revving motors drive entirely differently from a V8 and I have been jumped on by people who should know better when I mention some things (including Ranger who threw in with a troll on another forum once!). You can actually feel the difference on a cold start-up between, say, 10W-30 and 5W-30, by the snap of the engine off-idle, and even the engine sound is a little more muted with heavier oil (the Quad 4 was roundly criticized for NVH its entire life). But, once, the dealer put dino oil in my low-mileage 1997 ETC and I could tell instantly when I started the car. They checked, and indeed it was so, and they changed it again back to Mobil 1 for free.

Mobil 1 5W-30 is recommended to the consumer for cars where this oil is right (it has viscosity vs. temperature very similar to 10W-30 dino oil over most of the regular operating temperature range) on the basis of "better fuel economy." With its lower viscosity except at high temperatures and near-zero wax content, it will do that. But lower drag in the motor means that this power is going out the crankshaft, not into stirring the oil, which means a horsepower or two, and, I'm a motorhead. Other benefits of synthetic oil are keeping fluid at very low temperatures due to no wax content and holding on at very high temperatures due to very low light hydrocarbon content.

As far as going 10,000 miles between changes, well, if the OLM says so. But resetting the OLM is betting a $50 oil change against the life of a $5,000 engine. You won't see the difference for years, but it will be there eventually.

Some cars use flat tappets and/or have distributor gears or timing gears instead of timing chains, or other metal-to-metal sliding surfaces that are subject to wear while the engine is cold and until good oil flow gets to them. This is handled by oil additives (ZDDP and such) that have been cut in half since the early 1990's because these things are hard on the CAT. The GM OLM has a 100% margin so you can still use it with modern oils in such engines. But I wouldn't reset it and keep driving without an oil change. With a newer engine you have some chance of winning this bet. Me, I don't gamble with something as needful an investment as a daily driver.

[Texas Jim]

I change mine at about 30 to 35%... "UNLESS" I have ran it real hard.

Then I change it as soon as I can.

Oil is cheaper then engines....

[Cadillac Jim]

I would let the OLM decide how hard the engine must run to need an oil change. Particularly if you run synthetic, which keeps its film strength and viscosity better when it is hotter, I wouldn't worry about running it too hard so long as I kept it in drive, didn't tow, and didn't include such things as flat-out miles-long top-end grade climbs in 100+ F weather or some such.

The Northstar, particularly in VIN 9 trim, comes with oil cooler, transmission cooler, and power steering cooler, and was designed in 1992 to run with the big dogs on the Autobahn as a design. Even taxicabs on the way to the airport go 190 kph (118 mph) on the Autobahn. You can't run it too hard in Drive on reasonably level ground in commonly seen weather.

[Texas Jim]

I would let the OLM decide how hard the engine must run to need an oil change. Particularly if you run synthetic, which keeps its film strength and viscosity better when it is hotter, I wouldn't worry about running it too hard so long as I kept it in drive, didn't tow, and didn't include such things as flat-out miles-long top-end grade climbs in 100+ F weather or some such.

The Northstar, particularly in VIN 9 trim, comes with oil cooler, transmission cooler, and power steering cooler, and was designed in 1992 to run with the big dogs on the Autobahn as a design. Even taxicabs on the way to the airport go 190 kph (118 mph) on the Autobahn. You can't run it too hard in Drive on reasonably level ground in commonly seen weather.

I know you are right about the hard running, and I do use Synthetic oil.

But I feel better about it and it isn't nagging at my mind, if I change it after a trip where I have run it pretty hard for a few thousand miles.

The trip last year had some hard running... several hundred miles across New Mexico and across Arizona, and often in the triple digits for an hour at a time or more.

Then going into California and up the hill from Needles to Barstow.... there is a stretch there which is mostly UPHILL for about 25 or 30 miles.

The temps were over 115...

I changed the oil a couple of days later.

I knew I would have a long fast run back to Texas from Northern Montana... LOL

Probably could have waited till I got back home but.................

[Cadillac Jim]

I would let the OLM decide how hard the engine must run to need an oil change. Particularly if you run synthetic, which keeps its film strength and viscosity better when it is hotter, I wouldn't worry about running it too hard so long as I kept it in drive, didn't tow, and didn't include such things as flat-out miles-long top-end grade climbs in 100+ F weather or some such.

The Northstar, particularly in VIN 9 trim, comes with oil cooler, transmission cooler, and power steering cooler, and was designed in 1992 to run with the big dogs on the Autobahn as a design. Even taxicabs on the way to the airport go 190 kph (118 mph) on the Autobahn. You can't run it too hard in Drive on reasonably level ground in commonly seen weather.

I know you are right about the hard running, and I do use Synthetic oil.

But I feel better about it and it isn't nagging at my mind, if I change it after a trip where I have run it pretty hard for a few thousand miles.

The trip last year had some hard running... several hundred miles across New Mexico and across Arizona, and often in the triple digits for an hour at a time or more.

Then going into California and up the hill from Needles to Barstow.... there is a stretch there which is mostly UPHILL for about 25 or 30 miles.

The temps were over 115...

I changed the oil a couple of days later.

I knew I would have a long fast run back to Texas from Northern Montana... LOL

Probably could have waited till I got back home but.................

If the temperature gauge stayed below 3/4 and the OLM said so, I wouldn't have bothered to change a synthetic oil fill.

[Texas Jim]

I would let the OLM decide how hard the engine must run to need an oil change. Particularly if you run synthetic, which keeps its film strength and viscosity better when it is hotter, I wouldn't worry about running it too hard so long as I kept it in drive, didn't tow, and didn't include such things as flat-out miles-long top-end grade climbs in 100+ F weather or some such.

The Northstar, particularly in VIN 9 trim, comes with oil cooler, transmission cooler, and power steering cooler, and was designed in 1992 to run with the big dogs on the Autobahn as a design. Even taxicabs on the way to the airport go 190 kph (118 mph) on the Autobahn. You can't run it too hard in Drive on reasonably level ground in commonly seen weather.

I know you are right about the hard running, and I do use Synthetic oil.

But I feel better about it and it isn't nagging at my mind, if I change it after a trip where I have run it pretty hard for a few thousand miles.

The trip last year had some hard running... several hundred miles across New Mexico and across Arizona, and often in the triple digits for an hour at a time or more.

Then going into California and up the hill from Needles to Barstow.... there is a stretch there which is mostly UPHILL for about 25 or 30 miles.

The temps were over 115...

I changed the oil a couple of days later.

I knew I would have a long fast run back to Texas from Northern Montana... LOL

Probably could have waited till I got back home but.................

If the temperature gauge stayed below 3/4 and the OLM said so, I wouldn't have bothered to change a synthetic oil fill.

I know how the OLM works...

I understand the LOGIC behind it and how it figures oil changes....

Logically I know an oil change probably wasn't "NEEDED"... but.........

There is that little voice in your head that keeps saying...

"Well... maybe it does need changing"...

"It wouldn't hurt anything to change it"...

"Better safe than sorry"... etc.. etc..

The only way to shut it up and get peace of mind is to change the oil.

[Cadillac Jim]

I give. I would do the same for my baby.