On my 2001 Mustang Cobra I installed a bypass oil filter and started oil sampling with the idea that I would change oil when the samples indicated.

Bottom line: I got out to 33,000 miles on engine oil when I finally said enough. The bypass filter did a really good job of cleaning the oil and absorbing moisture that I didn't need to change oil.

I have a bypass filter on my FEH and use double the 10k called for.

 

Even tho I drive about 1,400 miles a month, the short trips to work during the week take their toll on my oil (Mobil 1 0w20). My mechanic uses Caterpillar oil analysis and from previous winter analyses 8k appears to be a good time. 10k miles works fine the rest of the year. It's not uncommon to see lows of -20 to -25°F here in the winter.

 

What in the sample results causes him to tell you to change oil?

 

Condensation (water or mineral deposits in the oil) from the short trip to/from work (.6 miles).

I don't let my engine idle, b/c it's not necessary and I don't feel driving a 3 mile route to work just to let the engine warm up more is warranted so I just have to change the oil more often. I drive 100 (or 500) highway miles on the weekend so it does get warmed up.

The test for antifreeze was negative, if that was your next question.

 

The Total Base Number (TBN) measures how much alkalinity is in the oil. Combustion produces acids and the lower the TBN, the less protection your engine has from corrosion. A TBN of 2 or higher is needed for adequate protection. Engine oil analysis can tell you many things about the wear and tear of various components in the engine. TBN analysis can be used to predict the useful life of the oil in the engine, assuming that your driving conditions do not change drastically.