from 82 to 87 I had a s10 5 sp manual 2.8V6. At that time Mobil did advertise 25 K oil changes. I used AC filters, changed at 12K miles. Oil Mobil 1 10W30 changed at 25K. Pulled bass boat 2700 lbs on trailer. Engine spent quite some time Wide open climbing Ozark hills. Probably 15% pulling boat.
At about 100K the crank shaft broke, trashing the engine.
The rest of the engine was pristine. No sludge, almost no varnish. The camshaft and lifters had almost no wear, still see honing marks in the cylinders, pistons tight. The engine was good for at least another 100K.
Unfortunate that GM undersized the mains a little and the cranks broke.
That engine was expensive, and the truck was pretty pristine otherwise. I sold the truck to someone wanting to V8 it. and used the money to buy a Monte Carlo SS that was a huge piece of [censored]. The last new GM I ever bought.
Rod