At what point does oil wearing out, changing viscosity, degrading,oxidating,nitration etc.start to increase engine wear.reading the post on the 50,000 mile oil change made me wonder if anyone has read a sae paper on this subject.
Any Oil starts degrading as soon as it gets circulated through the engine. Much depends on the engine and driving styles, but in many cases we see viscosity and other changes by 2,500 miles, especially in dino oils.
The amount of wear is determined by engine design and driving conditions.
I have yet to see any original oil go past 7-10k miles without serious degradation. I don't buy into the extended oil change intervals as a blanket statement for all engines and driving conditions, especially any so-called 50,000 mile oil.
Used Oil Analysis is the way to determine how well your oil/engine combination is functioning.
Take a look mat the UOA threads; lots of good info on varios oils and various engines.
Even with Delvac 1 (in a gas engine), I would not go past 5k without a Used Oil Analysis. Gas engines have smaller sumps than do diesels, so oil degradation is more accelerated in a gas engine than for a diesel.
In fact, I would sample at 1k to get a baseline, then sample at 5k. If the UOA oil showed stamina in that particular sample, and it appeared tbn, viscosity, and oxidation were under control, I would then go on to maybe 8k.
[ April 08, 2003, 12:51 AM: Message edited by: MolaKule ]
When the oil starts to get "yucky", it does so exponentially. So, the point is, to change it out well before then, whether using a preventive maintenance logic (change it out every "pick your favorite mileage") or predictive maintenance logic (using oil analysis).
quote: I have yet to see any original oil go past 7-10k miles without serious degradation
Define original oil. Define serious. I respectfully disagree....in a way. I guess you are saying, no filter changes, no top ups....the oil is pretty beat up in 10K...well OK.
On the other hand I went 20K miles. Yes the oil was tired, but did not look particularly "yucky", and analysis said it was not causing undo wear nor were deposits left.