A little off the topic but i wonder how many people think the oil light on the dash is to tell them the oil level needs replenishing ? We had some friends stay with us , they were about to leave and i said have you checked your oil level ? They had not so i did it for them , nothing on the stick . I said it's empty , they said the light hadn't come on yet so they weren't worried , they would put some in when they got back home (500 miles) . I told them the light heralded low oil pressure , not low oil level and once it came on , you had a micro second to shut the engine off . Ive since spoken to others who believe the same .
I always shake my head in wonder at that stuff even though I've seen it hundreds of times. At work I get them a lot. I can't stress enough the importance of reading the owner's manual.
I just recently put an engine in a 2005 Chevy trailblazer That had lots of hardened carbon(no longer sludge) clogg up the oil pick up screen and lock up the engine due to oil starvation. I've also seen oil fail 'cause thermostats stuck open and caused the oil to become very thick and milky 'cause the engine never got hot enough to burn off the moisture that builds up in the crankcase. I've seen timing chains in cars wear out the tensionors 'caused by lack of oil getting through the oiling hole, and the hole had to be drilled out for proper oiling. I wasn't smart enough to figure this out though, found it on a TSB(Technical Service Bulliten).
I've seen lot's of Toyotas and Fords with overhead cams sieze up from oil starvation. Once I put an engine in a Ford Probe Cause the cam locked up, broke the timeing gear off the end of the cam, and cause some bent valves and a broken piston.
I am by no means an expert on oil, but like many, I have an opinion on when oil should be changed, and it isn't the same as what the experts say. For me, I use synthetic in everything. I use two different kinds too, Amsoil signature series and BG synthetic. Depends what's on hand when I change the oil. The signature series is supposed to be good for 35,000 miles. Yes that's right, Thirtyfive thousand miles. Their oil filter is good for 25,000 miles. I've never went that far but I have gone 15,000 on it and 10,000 miles on the BG oil which is good for 15,000 miles. I check my oil everytime I fill up the gas tank and never have to add oil to my truck. My Prius uses about a quart every 3 thousand miles so it is my opinion that, since I have to add oil, the oil I add, replenishes the additive package in the oil and I can go even farther on that. Every time I change the oil in my vehicles I look inside the oil pan with a flash light and have yet to see even a slight change of color up in there. Still looks like the day it was put together. Nice and clean aluminum and steel in there, and that's with 160k on the Prius and 60K on the Silverado.
Oh yeah, when's the last time you flushed your trans, brake and powersteering fluid, and serviced your diffs and transfer cases? I see failures in those components more than engines due to lack of fluid changes.