Tom, our resident oil expert (I'm just a poser) mentions gallons of fuel used as a nice measurement of oil change interval. I like that idea as it accounts for hard useage (low MPG) and highway (easy usage, better MPG) but since I don't keep track of how much fuel I use, I end up changing it every fall with about 2 ~ 3K miles on it. Having the new oil sit in the oil pan over the winter is no problem and better than having the engine sit with potentially corrosive oil for those few months
I agree that with today's oils, especially synthetics like Mobil 1, 3K is on the low side. That said, 10K is way too much. Maybe the oil could make it, though you'll never know for sure if you don't have it analyzed for TBN (total base number), but your filter certainly can't. It will have long since clogged and go into full bypass, meaning that all dirt in the oil will continue to circulate certainly causing excessive wear. Is it worth it, to save $50.00 on oil?
Case in point. I ran 5,800 miles on a 2002 Chrysler product with Mobil's best available synthetic (Delvac 1) and used a Mobil 1 filter. 6 months of usage. My TBN was down to 3.6 and my insoluble hit the max at 0.6. If I ran this expensive oil (costs more than Mobil 1) for 10K miles without changing the filter, my wear numbers would have most likely been throught the roof.
Here's a bit more on TBN from the Blackstone web site (
www.blackstone-labs.com):
What is a TBN, and who uses it? In short, a TBN (total base number) measures the amount of active additive left in a sample of oil. The TBN is useful for people who want to extend their oil usage far beyond the normal range.
By comparing the TBN of a used oil to the TBN of the same oil in ****** condition, the user can determine how much reserve additive the oil has left to neutralize acids. The lower the TBN reading, the less active additive the oil has left.
An oil's function is to lubricate, clean, and cool the engine. Additives are added to the oil to enhance those functions. If the oil becomes too acidic, it will corrode the engine. A good TBN result, meaning plenty of active additive is left in the oil, is usually in the 6.0 to 14.0 range (depending on whether the oil is for gas or diesel engines). A low test result, meaning very little additive is left, is down around 2.
Scientifically speaking, the TBN is one of two "neutralization number" tests run on oils. The TAN (total acid number), which is used for hydraulic oils, is the other. The TBN measures the total basedity of an engine oil; that is, how much base (as in, a base vs. an acid) additive is in the oil to offset the deleterious effects of acids coming into the oil from combustion and other sources.
However, the TBN is not the only factor to consider when determining how long an oil can be used. If wear accumulations and insolubles in the oil build up and become abrasive, we would recommend changing out the oil, no matter how high the TBN reading.