In Reply to: Re: Oil tested after 10 years use. posted by TheOldHokie on December 10, 2018 at 14:10:03:
True that chemical changes and contamination are destructive to gasoline powered engines' oils. Oils can be reclaimed by centrifuging, using chemical cleaners and addition of new additive packages.
A single (insignificant N sample size) example from a small air cooled under stressed engine isn't a definitive test.
Coolant contamination is another factor affecting lubricant performance. Quality of the oil, the efficiency and maintenance of the filtering system play a large part of the longevity of engine oils.
Modern truck engine manufacturers have introduced extended oil drain programs. Detroit Diesel has extended their recommended drain intervals to 75,000 miles, Navistar to 60,000 (IIRC) Cummins to 50,000. Oil sampling is recommended at each filter change, typically 7500 to 10,000 miles. Big saving in operating costs. 12 gallons of oil @ $12 to $20 a gallon plus filters at $16-$20 per, recycling fees, along with shop and down time.
I assume the engine manufacturers have worked closely with the oil companies in the implementation of those increases.
I used extended oil drain intervals in my CAT powered equipment and got extremely long life from them in spite of being in service before I obtained the equipment and used in start stop operations. I doubled the number of the filters originally installed, sampled the oils at the time of filter(s) change and followed CATS' recommendations for TBO based on the PPM of metallic elements in the oil. I had no oil related problems and got extremely long life from the engines I operated. Initially Cummins then CAT for the majority for the years I owned class eight trucks. With engine overhauls running $12 to $15K and reman factory engines in excess of $25K (2006 prices, the year I retired) I wasn't going to take any chances.
Any IC engine burning dinosaur fuel is going to contaminate oil, period. DIesel engines much more so than spark engines. LNG and propane fueled engines don't contaminate the oil installed, unless coolant intrudes or dirt is ingested through the induction system. COmpressed gas fueled fork lifts and mining equipment run thousands of hours between changes. The oil and spark plugs look like new when removed.
I still do oil sampling every other oil change on my cars. So.....yes modern oils retain their lubricating ability for a long time but it is finite.