First post here, I've been a guest reader for quite awhile tho. Actually have something to add to this post. I've got a collection of older vehicles (I like 70's stuff) but 3 others are relevant here. 2005 Chevy Cobalt. Bought new, have always followed the oil life "recommendation" which usually ends up between 6000 and 8000 miles, mostly 7500-8000 before reading 0%. Completely aware this is based only on a algorithm and does not "sample" oil, or know whats in the oilpan. Car currently has close to 265K, with nothing more than an alternator at 238K and heater core around 245K. It's had mostly 5w30 of ALL types and flavors, with a 15-40 or 10-30/40 a few times based on what I had or was on sale. Still runs great, no leaks or noises. Consumption has gone from NONE between changes to 1 qt/2000 miles or so after oil life drops below 75% range or so. So I've just learned to check it about every 20% of life drop on indicator. Prob try some 20w-50 once it warms up.
Next is 1992 F250 4x4 460. Slightly over 270K. Engine never been apart, does have some timing chain slack as observed by watching rotor while turning crank back and forth with breaker bar. Runs great tho, pulls a 10K boat some and does not use oil between 3-5K changes. Bought it from orig owner, worked hard he had replaced trans once and was out when I got it. I use either Brad Penn 10w-40 or 20w-50, Delvac 15w40 or last chg was Pennzoil High Mileage 10w-40. Rear main had started weeping and the HM appears to have dried that up for now.
Third is a 1995 GMC K1500 5.7 TBI. Bought it from original owner at 255K (he is a Toyota mechanic at local dealer) so it was well maintained. Original engine and trans. He said he always changed oil at whichever dealership he worked at, bulk 10w30. Runs great also (son's truck), does use a quart or so in 5K miles.
Personally I'm not a fanatic about oil or overly frequent change intervals, but NEGLECT will kill any longevity. Not a huge fan of thin (xw-20, xw-30 stuff in older flat tappet engines either, although I think its likely OK in newer roller engines not subjected to extreme use HP or TQ wise.
Boat has a GenV Mercruiser 502 MagMPI, nearly 500hrs on it. BradPenn 20w-50, Merc recommendation is their branded 20w-40. No issues so far.
