My experience with 40 weights...

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Jul 16, 2008
Massena, NY
has been a great one in my 4.7 Jeep. I decided to use Rotella 15w40 this summer because I do a lot of off roading and some towing. The engine is noticeably quieter and smoothing. Some people say there is a little power loss but my [censored] hasn't felt anything. I have also heard fuel economy suffers with thicker oil. Well I just got 19.8 mpg mixed driving with E10 gas! The best the Jeep has ever gotten! I'm happy 15w40 in the summer in this engine. We've had a few 30 degree mornings and after 8 hours of sitting in it there is no knocking, tapping or anything. But I think I'll stick to my Synpower 5w30 in the winter.
I've been thinking of going to a 40 weight oil in the subaru after my PP stash is up. Most likely M1 0w40 or RTS.
Originally Posted By: toyotaguy
I think Mobil 1 0w40 is a great oil

Yep. Especially if you want a 0w30.
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