Anyone have an opinion on it? What milage would you begin to use it? I have an 05 hemi with 9k miles on it. Thanks.

 

I've used the API rated RP 5W20 in my 2005 Ram Hemi. I've found it to be a bit thicker than Mobil-1 5W20 in the winter. RP doesn't have the notorius "tick" sound that I had with M1. Gas mileage was the same in warmer weather. UOAs show that wear was the same between M1 and RP except that RP had 3x the copper wear. Can't explain the copper. My current thought is that it's an aberration and I'll wait for the 2nd UOA before making a final decision.

Since M1 and RP check out about the same from a wear perspective, it really comes down to price. M1 can be purchased nearly everywhere and from Wal-Mar for around $4/qt. RP can be found online or in a few retail stores. I've never seen RP 5W20 in any store, though. Cheapest price for RP was $5.70/qt from eBay.

All things considered, RP, M1, and no doubt many other synthethics will perform about the same with change intervals in the 3k-6k mi range. Beyond that, I only know that M1 holds up well. Amsoil has always thickened out-of-grade in every vehicle once I've gone over 6k mi. Currently running a >6k mi change interval on 2 vehicles with RP and won't how it holds up till the fall.

My vote: go with the cheaper and more available products. It's less hassle.

Roger...