I've searched the threads a few months back, but my question is almost too basic. I put very low miles on my Rig - perhaps 6-8k per year. I never hit the mileage before the date due on an oil change. If the truck oil levels are ok, can I just wait for the appropriate mileage to change oil, or I am harming the engine having "old" (time-wise, not mile-wise) oil running? 97 with 67k. I appreciate it.