I wouldn't use oxidation to tell the life of the oil, especially since I've found most labs don't properly calibrate their machines to read oxidation accurately with synthetic oil.
With the lab I use, the oxidation numbers are always 2-3 times higher than they should be, even Terry Dyson has noticed that when doing my interpretations.
This brings me to another point, if you truly want to find the right interval for your car, and push your oil changes further, you should be using Terry's services, he truly knows how to read UOAs better than anyone else out there.
Thanks Pat for recommending Terry.
On the other hand I am trying to learn as much as I can for free !!!
The UOA are fairly new to me, I get it especially to monitor the intake manifold coolant leak on my engines.
Without that problem I would go with dino at 5000km like I did all my life.
Terry is certainly good but having to spend 20.00 US on top of 20.00 caNADIAN for an oil analysis...no thanks.
I'm sure that the level of knowledge is is sufficient what for what I want to learn.
BTW thanks for your input its really apprciated.
As a general rule-of-thumb, the oxidation rate of the oil will double for every 10 degrees C increase in temperature. From this, the logical conclusion may be drawn that the life of the oil will be halved at the same time. Used oils can be re-refined, contaminants removed and additives replenished to provide a product like new, but if excessive oxidation has occurred, then there is very little that can be done to rejuvenate the oil. A Noria piece that may add to this thread.
Oxidation is "damage" to the oil itself. Nitration is caused by combustion gases reacting with the oil. Both are indicators of the remaining life of the oil, with nitration also an indicator of the mechanical health of the engine...piston ring blowby or leaking EGR valve.