Increased MPG by using 5w20 vs. 5w30?

[Leonardo629]

well..I don't keep a stopwatch in my glove compartment.....

but Motul designated their 300V 0w20 weight as their "qualify" oil for a reason.....

 

[Leo]

Yeah and what happens to qualifying engines after they're done?

Haha!

 

[philipsearcy]

I went from Motorcraft 5W-20 to Mobil M1 5W-40 in my 2004 5.4 F250 and did not see any changes in MPG. I do not think you will see MPG differences in such large, heavy, and aerodynamic ineffecient vehicles. Philip.