Quote Originally Posted by zebra View Post
okay... so here's a question for all y'all.

my truck: 99 NBS RCSB with a 4.3/5-speed & 4x4

at 135000, i switched from 10W-40 conventional to Mobil1 10W-30 & Wix filters. runs great for a year and a half... but now at 148400, i don't know all the specifics, but it has something to do with a bad rod bearing, a broken rod and the engine can now be best used as a boat anchor.
i was told by the mechanic (who is a long-time family friend & very trustworthy as well as having been mechanic-ing for 40yrs) that it was because i switched to full synthetic, & it washed off all the shellac on the bearings, which then collected in the bottom of the pan & clogged the oil pump. then he showed me at the very tip of the dipstick where it was a bit darker & thicker. that makes me wonder why i never heard of anyone else switching to synthetic & having the same problem.

have any of y'all ever heard of that scenario?
I smell some bovine excrement but listen to some other experienced techs.
My tech said to keep synthetic if you are using it and if you have used regular for many moons keep regular so you do not develop leaks.