Quote:
Originally Posted by mav1178
If you are not testing your oil on a regular basis, then the answer is yes, they do "go bad". They don't suddenly break down but oil health is like bloodwork, it tells you a lot of detailed info about the health of your engine internals.
Oil change intervals should be lengthened only with the use of oil test results that have a known time or mileage interval... otherwise you're just making good guesses with no basis in fact. You should swap out the fluid if you're even under recommended mileage intervals, because you have no way of knowing how much additives were consumed already up to that point.
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Much of that depends on how you are using the car. Not many people get analysis done. Oil sitting in an undriven car is not any different than oil sitting in a jug. It is not breaking down until the car is running. Swapping out early based solely on a set period of time has no real advantage. Test or no test the oil needs to be used to break down. Now of course changing early doesn't hurt anything either.