Originally Posted by Labnerd

Camarothatcould, I assume that you are talking about your 98 Ford. It is speced for 5w-30 oil meeting the now current 929 spec. I would not suggest putting the Rotella in it. I think you have the wrong info anyway, Rotella that you are talking about is a 5w-40 or a 15w-40. Either will be thicker at temp than the design perameters for your engine. The oil and internals will run hotter, not cooler as a thicker fluid does not absorb and release heat as quickly as a thinner fluid. The 5w-20 oils will run far cooler when things get hot under the hood. You also have more fluid being pumped as thinner fluids move faster to the job than a thicker fluid so there is more lubrication using the thinner oils. Many years ago we recommended the heavier oils because the oil film strength would break down under load and heat. The heavier oils had better film strength. No so with todays oils and the 5w-20 oils will have greater film strength than the 15w-40 Rotella due to the basestock used. Either stay with the 5w-30 or use the backward compatible 5w-20. I'll bet the noise goes away with a run of the 5w-20.
On your GM engine. I hope you have a LARGE supply of the Rotella in CH or CI API rated oil. The new CJ oils (for low sulphur engines)will be missing the additive package that your modded engine needs. Have you looked into CD2 Street Legal Oil Boost? It can be had a some of the Dollar stores and is full of the add pack you will be needing. Also, GM Oil Booster, while not cheap, is another alternative for you. Or, for now anyway, using an oil high in ZDDP like Amsoil could be an alternative.