I run Valvoline conventional 10-W-40 in everything I own. Engines stay clean and I rarely have engine trouble even with high miles. I change my oil about every 3K; if the oil still loooks relatively "clean" sometimes I'll go 4K but never any more. everything I have is cam in block (OHV) timing CHAIN (no belt) 2-318s (carbureted, my truck is daily driven, Fury is seasonal) and 2-4.0s (97 Wrangler and same yr Cherokee)