GM Oil Life Monitor

[WTA]

I have rebuilt a LOT of engines in new cars where people believed that oil life monitor. I mean a LOT! 3000 miles was and is the standard for a good reason. Especially if you drive in the city a lot.

The oil passages in these new engines, especially in the lash adjusters(used to be called lifters) is so small that if you saw one you wouldn't understand how even clean oil can get through them. Add a little sludge and carbon buildup and you got problems.

It's really best to stick to 3000 miles unless you are going to trade it in when the warranty is up.
That's why I will never buy another used car though unless I see service records on it from a dealer I trust.

That Oil life monitor is just based on time and miles. It has nothing at all to do with how the oil is actually holding up. I have done oil samples a lot in the past. In the Army, Navy and for a large civilian truck fleet. The Navy almost never changes oil. They just purify it and add new to make up for whatever is lost. Thats for ships though. The purification process is great.

The Army changes depending on the results of oil analysis on vehicles that sit a lot. Usually every oil sample I processed had more water in it than I cared for and was lacking in additives but we had limits that told when to change it.

That civi truck fleet changed oil about every 3-6 months. This is on engines holding 40 quarts though and rarely shut off. They may have 10000 to 50,000 miles on them but still it's synthetic oil and 40 quarts of it. Also they usually leaked enough that the drivers were adding a gallon or so ever couple days. That kept the additive package in spec pretty good.

I used to do samples on my truck engine. It was maintained in perfect condition for hundreds of thousands of miles and the samples always told me to change the oil around 3000 miles. That was usually 2 weeks to once a month for me.
In nearly 1 million miles I only had to do one minor overhaul on that engine.
If you really want to spend a small fortune on a new engine go ahead and follow that monitor. I have seen too much to go past 3000 miles on anything I own.
I haven't even gotten into which brands of cars and oil are more prone to going bad. I could though. I definitly have some good fact bast opinions about oil brands and car engines.

 

[JSharp]

The current GM oil life monitor is substantially more complicated that just a time and mileage counter.

Here's a decent technical discussion of it -

GM OLM ? - Bob Is The Oil Guy

That board has dozens of oil analysis reports from people that followed the OLM. Not one has shown the oil condition to be a problem when the OLM claimed it was still suitable for continued use.

The possible exception is the classic GM "intake manifold leaking antifreeze into the crankcase" failure. 3000 changes won't help you there in any case. You need to fix the problem...

 

[anthonyk]

Guys, I posted this the other day on another string here, but thought you might appreciate it:

I'm one of those guys who used to go to Jiffy Lube or the dealership every 3000 miles for oil changes but now do my own.

3 years ago I bought a Dodge Ram 2500 with the Cummins diesel engine.
The oil changes were 80 bucks a piece at the dealership!!!
After the breakin period of about 7500 miles, I switched to Amsoil Heavy Duty Diesel.
It cost a bit more, than most synthetics, but not much.
Every 10,000 miles I change the filter (Donaldson-about 12 bucks) and sent them a small sample for analysis (I think about 15 bucks).
They do a complete analysis of the oil explaining it's properties such as soot, iron copper, lubricity, etc (this can be useful in predicting maintenance) and tell me to either keep using it or change it.
I don't change it until they tell me.

Well, I just changed it for the FIRST time and the oil had 95,000 miles on it!!! No joke.
So if I'd had regular oil and done the scheduled 3000 mile changes, it would have cost me $2,533.00 over the last 3 years.
Instead it cost me $243.00 plus the initial oil cost ( I can't remember exactly, but let's say 50 bucks to be safe)
So instead of $2,533.00, I spent app. 300 bucks, did less work, had better oil, and didn't have to dump 81 gallons of oil into the environment. I saved approximately $2,233.00
In my book it was WELL worth it.

anthony

 

[WTA]

I wonder how many new engines he has rebuilt? I've worked at new car dealers, used car dealers and big truck shops since I retired from the service and I've rebuilt way too many that would have been fine if the oil was changed more often. My last job was at a used car dealer and this nice old lady that was a good customer bought abuick from us with that 3.8 in it. At 30,000 miles it threw a rod and we put in a new engine from the dealer. At 45,000 miles I had to rebuild it for being so plugged up it was losing oil pressure and knocking. I won't even say what brand of oil she was using because I've been down that road before. She was following that oil life monitor though and having it changed at the oil change place next to my shop. She only changed it twice in that 15,000 miles. That's just one example that comes to mind. One of many. Buicks are actually pretty good cars I think. There is another brand that I wouldn't own if it were given to me.

The problem with these engines nowadays is all the dissimilar metals, hotter operating temps and stop and go driving.
Almost every Chrysler engine I rebuilt was so gunked up inside it was amazing the oil could even drain out the pan plug. The ones I rebuilt from high mileage mechanical failures was rare. Oil related failures was all too common. Most people just have no comprehension how complicated a new engine is. Many have 2 or 4 overhead cams with 24 or more lash adjusters or more, variable cam timing, timing chain hydraulic adjusters and all sorts of other stuff that just will not tolerate dirty oil or sludge.

I just recently gave away all of my specialty tools for new Ford engines because I won't ever own one again. The last 5.4 I had to rebuild made up my mind about that. I love Fords but a truck needs to be simple, hard working and reliable. I'm not having something I can't fix on the side of the road without special tools. Plus my old 91 truck with the good old 5.0 got just as good a mileage as the new ones. Better if I kept my foot out of it.

If you are using high quality synthetic oils and doing a lot of highway driving then this oil thing isn't going to be a problem probably. Abuse it in stop and go stuff and it will though.

I know that oil life monitor is a little more complicated than I said. Basicly that's all it does though. I am very familiar with the computer systems. Enough that I know not to trust them when to change my oil especially. I still get called back to the last dealer I was at to diagnose computer problems.

My Powerstroke I do run about 6000 to 7000 miles between oil changes. BUT, that's because I know it's good for it, it holds a lot more than a car engine and It's all highway miles on it. Still it's barely a month between oil changes on this one. I've been running castrol in it. It's good oil too until it breaks down. I just had one of my valve covers off though and it's squeeky clean inside there. I've never tried Amsoil but always heard it was good. I wouldn't be scared to go that far on a highway driven diesel as long as the oil is holding up. You don't get oil that good at quick lube shops though. The big advantage you have over a powerstroke though is I have a high pressure oil pump and you don't. This is why I won't go any longer than I do. Those pumps work great but they sure are expensive when they break. The hydraulicaly run fuel system on the powerstroke is very Dependant on clean oil. Both the cummins and the powerstroke are some working beasts though.

 

[MrJimi]

Well, I just changed it for the FIRST time and the oil had 95,000 miles on it!!! No joke.
So if I'd had regular oil and done the scheduled 3000 mile changes, it would have cost me $2,533.00 over the last 3 years.
Instead it cost me $243.00 plus the initial oil cost ( I can't remember exactly, but let's say 50 bucks to be safe)
So instead of $2,533.00, I spent app. 300 bucks, did less work, had better oil, and didn't have to dump 81 gallons of oil into the environment. I saved approximately $2,233.00
In my book it was WELL worth it.

anthony

Anthony, am I reading this right ? you went 95,000 miles on your oil before you changed it ?
YEOW !!!
Jim

 

[WTA]

I've been thinking of switching mine to that brand and I think I am now. That truck fleet I used to work for used it too and went that long all the time. It is good stuff.

 

[Z71]

I got a 93 Lumina sitting outside that has had yearly oil changes since new, now just shy of 100,000 miles on the car and 80,000 were driven by a little old lady (my mother). Back when she got the car the salesman told she had to change oil every 3 months or 3,000 miles, whichever came first. She could not afford doing that driving less the 10,000 miles a year! So we did what I have been doing since 1975, put in Amsoil synthetic and changed it every spring. She don't drive anymore and I now use the car in the winter months to save on my Cadillac. In those 100,000 miles it has NEVER used a drop of oil. Just think of all the money she saved! 3 changes per year was the dealer's advice, they used to send her reminders all the time to come in for a oil change. Lucky she listened to me instead and saved a lot of money. The body is going to rust away before this engine wears out, it has never been touched except for two tune ups, at aprrox. 40,000 and at 80,000.

Back in 94, I had the local trans pro purge all the oem ATF and fill it with Amsoil too.

If you want to use the cheap no-name brand oils than maybe you better change it at 3,000 miles. I don't believe all these stories on engine rebuilds. Local dealers around here tell they have not rebuilt engines in years and years, its much cheaper to use a new engine that spend hours on labor rebuilding something. I know someone here who just turned over 200,000 miles on a 10 yrs Buick LaSabre. He drives it 200 miles a day to work, he bought it with 90,000 miles and it was using Mobil 1 since new. He called me (knew I was a big synthetic oil fan) and asked if he could continue to run it. He was paranoid about going the long drains even though the previous owner had no trouble with the car. Money is all he thinks about and it was not hard to show him how much he could save, now he brags about it. Btw-He has hit 5 deer in 3yrs, once hitting 2 in one weeks before the adjuster has a chance to see the first hit. He would gladly wreck the car for the meat! LOL Oh, he also hit a Moose but had slowed down to about 10 mph when that happened so the damage was light. He a construction project inspector for the state dot.

I worked for 30 yrs (retired) as a surveyor for a state DOT and we changed our oils every 5,000 miles or 180 hrs of service irregardless of time on our work vehicles. The complete state fleet was like that since I stated in 1972. We were not permitted to change it sooner. Vehicles were scheduled for replacement when they hit 100,000 miles but it took a year to get the money appropriated into the budget, often it took 2 yrs. Never did we have engine failures.

My 2005 Cadillac gets the oil changed once a year, roughly 7-8000 miles, my trucks the same thing.

I know about 6+ diesels owners using Amsoil 15W-40 AME on yearly oil changes. The 3 longest ones go about 15,000 miles a year. 2 Fords and one Chevy. The other guys just work the trucks hard, contractors who can't afford down time. They all swear by it and claim it has saved them a lot of money.

All 4x4's
1999 Ford e.cab SDF250
2000 Ford cc SDF350
2003 Ford cc SDF350

2003 Chevy E. cab K2500
2004 Chevy reg cab K2500
2007 Chevy e cab K2500

+ 2 Dodges
199?
2006

I got a complete explanation of how the GM OLM works on my home PC. If I can remember, I will post it later.

 

[Z71]

Here it is. Note the person credited at the end was the Project Engineer on the GM Oil Monitor Project.

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

 

[anthonyk]

Mr. Jimi, yep, that's correct: 95,000 miles on one oil change.

Even ordinary petroleum oil is being changed way to often. The 3000 mile suggested change is a crock in my opinion. Even the owners manuals recommend 5000 to 7500 mi. changes.

Still it all comes down to proper filtration and a good oil to start with.
I'm sort of laughing though: When I first bought the Amsoil, I bought enough to have for future oil changes. Now I've got something like 10 years worth of oil out in the barn!

Anthony

 

[jayhaitch]

I had a 94 Yukon 5.7 TBI I bought used with 50,000 km on it. I installed the Amsoil dual-guard filter, a remote filter mount with a full flow filter and a bypass filter. The bypass filter remove contaminants down to a very small particle size, can't remember exactly, but only flows 10% of the full flow filter. I changed the full flow filter twice a year, and the bypass filter once a year, with an annual oil analysis. I sold the truck with 114,000 km on it, and never changed the oil. The oil analysis kept saying the oil was fine for continued use.

There's no space in the silly packaging of my 5.4 Expedition's engine bay for a remote filter, so I've been doing annual oil changes with Amsoil 0W30. I used a spring and fall oil filter change with their SDF filters, but now gladly have switched to annual changes with their Ea filter. I'm doing the same with my wife's Pacifica, also OW30. We do about 12-18,000 miles (20-30,000 Km) a year.