Maybe if the engine is always running hotter than when naturally aspirated. If you are running a turbo or centri that shares the oil supply, then I bet you'd want the heavier oil.

The Mobil 1 5w30 is not much heavier than a 5w20, so it probably doesn't make much difference.

 

I am running RP 5w20 and a Motorcraft filter. I wanted to stick with what the manual said.

 

Depends on where you live and your driving habits.

I live in the Phoenix area so 5w-20 during most of the year except during the summer. It's brutal here at that time so I want the higher temp capacity the 30 part of 5w-30 gives me.

 

READ THIS

I have it on good authority from one of the Ford engineers on the 4.6 3v Mustang engine. He also worked for Rehagen Racing in Grand Am (FR500c's), and is now an engineer for Michael Waltrip Racing.

He can only say so much without getting himself in trouble, but he specificly said he would NEVER run anything less than 5w30 in a modular engine. Period. Considering he has logged more dyno time with the 3v than likely anyone, I took his advice.

 

Scott Whitehead. We've been over it a million times here.

 

These oil question are everywhere, even on import forums.

http://www.tundrasolutions.com/forum...e-toyota-my-3/

Import trucks that is.

 

That's hearsay and it's inadmissible! I watch Judge Juddy, I know how this **** works, lol!

 

http://www.machinerylubrication.com/...?articleid=518

Here's an article about this very topic. I'm still reading, so don't know how it ends.

 

Did you finish reading it yet? How does it end?

 

The ending wasn't that great, but they pretty much said what everyone else has said, the CAFE standards are the reason for the 5w20 switch.