[Spridgets] On modern engine oils

[Michael Rowe]

On oils for the flat-tappet Onan generator used in my RV:

  I have had 2 oil related failures in Dodge smallblock engines. ...... These were all on the engine in my 70 Challenger, which is turbo, so it has a very mild, low spring pressure camshaft, that is actually less hard on the parts than a stock cam. The engine has pushrods and non-roller rockers.

  Failure one-Brand new engine-new rockers (stock) and shafts. Broke in engine on Castrol 30 weight dino oil (SJ rated) for 500 miles. All was good. Switched to Amsoil 10-40 oil (SM rated) and had lifter noise in less than 200 miles. The pushrods and rockers were burned up. 

  Failure two-put in new rockers, shafts and pushrods. Disassmbled the engine to clean it out and check the camshaft, which survived. Put it back together and broke it in on the 30 weight again for 500 miles without issue. Amsoil recommended going to 15-50 diesel oil, which I did. Lifter noise again in 250 miles, with another set of burned up rockers, shafts and pushrods.

  Gave up on Amsoil-rebuilt everything again-broke in on the 30 weight and switched to Mobil1 20-50 oil (SJ rated). No issues in 7 years to this point.

  The previous engine to this had run over 60,000 miles, over 15 years, with the same style parts, on SJ or older oil, without issue. All of the failures happened with the newer oils. The diesel oil was said to be higher zinc, but it turned out to be just SM oil with the soot additives, when it was tested. The other oil than failed was SM.

  The Onan is the exact same style of engine as the older car engines, overhead valve/flat tappet/non roller rockers/pushrods, ....