There is a book waiting to be written about automotive oil life monitors and what they can and cannot do.
The easy answer is that it is highly likely that the autocompany in question has done their homework and that their on-board oil life monitor can be trusted....and that it will have a fair safety margin as to when it recommends changing the oil. I would endorse following the oil life monitor.
Many reasons for confusion on the oil changing subject:
Oil quality has changed dramatically over the years and is easily capable of longer change intervals than oils in the past. Even in the last few years oil additives and base oil and viscosity improver stock has improved making this possible. Current oils have much higher temperature capability than older oils. This fact alone guarantees more miles between changes due to oxidation rates.
All engines are
NOT created equal when it comes to oil change intervals. A 66 Chevelle muscle car engine will need different oil and much more frequent changes than a 2008 Malibu. Engine
design has a GREAT deal to do with it. Older engines had rubbing element lifters, distributor drive gears, spur gear oil pumps, rubbing element rocker arms, etc. etc. all these "features" require far more of the lubricant than modern engines and wear out the oil (or use up the antiwear agents) much quicker. This is the first place to become suspicious of
ANYONE that mandates a singular change interval (like every 3000 miles) for all engines. Just does not compute.
Nor can you go back and use the logic of 8000 or 12,000 mile change intervals commonly seen on newer cars on older vehicles since they do not age the oil the same at all.
Modern engines have roller tappets, roller rocker arms, roller cam followers (OHC), gerotor oil pumps, no distributor gears, roller chains, etc. etc. All these features make the engine much more robust for oil quality, do not tear up the oil nearly as much and allow much longer oil change intervals as the engine does not treat the oil as bad and can run with much more degraded oil than in the past with absolutely no problem. In addition, the PCV systems for cleaning the crankcase oil of contaminants (fuel/water/combustion byproducts) have all been significantly upgraded on modern engines which significantly extends oil life. Many modern engines that have very long change intervals run larger sumps (6 or 7 quarts vs. 5) which also allows extended change intervals.
Just because one engine has a sludging or deposit problem with the oil does not mean that the change intervals of other manufacturers are wrong. Toyota has a huge problem with slugde formation in some of their engines and still recommend relatively short change intervals becuase of this. Their PCV systems were pretty ineffective on those engines. Not all engines are equal when it comes to oil life.
As mentioned, driving cycle is the single largest factor in determining when the oil in any given engine should be changed. Short trips are much harder on the oil than long trips....although much urban driving is fine since the oil does get warmed up. Winter driving is much worse on the oil than summer driving, period.
For the record there are engines out there with oil quality sensors as well as the more common oil life monitor that resides as software in the engine controller that models engine oil life based on engine operating parameters. Some engines use both. Software is simple and easy and VERY reliable as no moving parts are added. Software sytems are also relatively inexpensive for the vehicle as no additional sensors or wiring is required. Any of the oil quality sensors require wiring (along with the actual sensor itself) , create a potential failure and leak path and have proven to be somewhat troublesome in the field. Some react to addtives in the newer oils as well as contaminates.
Not all oil life systems are equal. The first of those systems were developed by GM and released back in the 1986 model year. The GM systems are extremely sophisticated models that were developed based on oil quality sampling techniques as miles accrued on the development vehicles. The GM systems use all the engine operating parameters, ambient and oil temperature, trip length, soak times, etc. to accurately model the engine oil life. Each vehicle is calibrated for that specific powertrain and then validated against actual oil life (via sampling) on durability vehicles. I have personally worked on a number of these programs as well as the development and validation of the original oil life monitor programs back in the 80's and can assure you that the oil life monitor is uncannily accurate and always has a significant safety factor regarding oil change interval. The oil life algorithms have seen a lot of development since they were first developed in the early 80's at GM and they are even more accurate today.
Each time you start the engine the affect on oil life is slightly different from the previous trip. That is pretty hard to keep track of mentally...i.e....how much "long trip" and "short trip" time has accumulated as well as how do you weight each trip accordingly. This is one of the beauties of an oil life monitor. It is always tracking and decrementing the oil life accordingly.
I would recommend following the oil life monitor. No manufacturer is going to put a system on a vehicle without validating it to some extent. The systems that will recommend the longer change intervals are typically the more sophisticated and accurate to ensure adequate safety factor. Simpler systems will be based on less variables and keep track of less things but are still much better than guessing. Many GM vehicles will repeatedly run to 12,500 or 15,000 mile change intervals with absolutely no concern over oil quality. Been there and done that too many times to tell. I trust the GM oil life system completely.
I spoke to a customer once who was basically lambasting the oil life monitor on his 1997 Eldorado as being "out to lunch" because he "read" that the car should go 8000 miles between change intervals and his oil change light was coming on in 1100 miles. Turns out he lives in a northern city. In the winter he started his car outside, drove gently stop light to stoplight for 6 blocks and parked outside. Did the same in the evening. Used a different car for long trips on the weekend. I was surprised the oil lasted for 1100 miles in the winter under those conditions!!! If he was following Click and Clack he would probably have used the 3000 mile change interval and been ruining his engine.
There are many many things that determine "oil life" or define when an oil is used up or worn out. Key parameters involve oil oxidation levels, acidity of the oil, contamination by fuel, contamination by water, contamination by other combustion by products, contamination by dust/dirt, contamination by wear particles, the amount of anti-wear additive left in the oil....... The commonly used anti-wear agent ZDP (or ZDDP) in oil is sacrificial and is used up over time. When depleted to low levels the ZDP is not effective since there is little of it left. An oil could be completely clean of contaminates and have low levels of oxidation but be ineffective due to the ZDP being depleted....typical of an oil in a modern engine at 15,000 miles in long trip driving. Similarily, an oil could be heavily contaminated with high acid levels at 1500 miles.....typical of the customer driving 6 blocks in the city and multiple cold starts in the winter.
That is why it is so hard to predict a change interval for each and every customer as there are many different ways the oil can fail and require changing. And that is why the oil life monitors were developed in the first place. This way each individual customer has a customized change interval computed for them and it is constantly monitored and updated to accurately predict the oil life, maximize the usage of the oil to prevent excessive cost and waste while completely protecting the engine. Without an oil life monitor any "recommended" change interval by any manufacturer must be relatively conservative and thus be much too soon for many customers....while still having the possibility of being not conservative enough for that guy in the city.
This is one more reason GM pursued the computer model oil life monitor vs. using a sensor. The oil life model can predict oil life for the future and modify the scheduled change event as the cycle progresses. That is why it is expressed as "Percent of Oil Life Remaining". This way the customer can react and change the oil in an predictable fashion rather than panicing because a sensor just said the oil turned "bad" due to a capacitance or resistance change.
Hopefully this helps some...... Once again, there could be a text book written on all this so it is hard to cover in one post, even a long one. Sorry for the typos I'm sure are there.....
