a guy i work with has an 04 3500 with a 6 speed transmission. i havent heard any numbers yet, but he claims that he gets slightly improved fuel mileage when his air filter is dirty and nearly ready to replace. any possible ideas why this might happen?

 

with the fuel prices, i'm to the point that i just put fuel in it and go. i do check to see how many miles i got on the tank, just to make sure there isn't any major drop in mileage, otherwise i don't check the mpg at all.

 

Never heard of that happening. It's the opposite for me- changed a dirty air filter to a new Wix one and went from 16.5 to 18.5 MPG. (3/4 ton automatic)