stocksr

Afternoon all. Got a question or a request for experiences with the Donaldson M085171 (40", 4" Inlet/outlet) muffler.
I had this muffler installed 2 weeks ago and from my calculations (that I make on a weekly basis from a twice weekly 104 mile trip) the Donaldson has decreased my MPG from a 16.75 average with a stock Muffler to 14.5 MPG. Anyone have a similar experience? The muffler is installed with the correct oreintation as the Arrow with "INLET" is pointing toward the front of the truck. Mounted in the stock location.
If anyone else has had the same result with this muffler or has a suggestion for why this might happen please let me know. I was expecting a 1.5 MPG shift, just not that direction. Thanks.

Shorts

Are you pressing on the go pedal trying to hear it?

stocksr

Not even a little. Just trying to drive consistent to get an accurate reading. If it cost me 2 plus MPG I don't care what it sounds like.

Mr Bee

I find that very interesting, I put on a donaldson Longer I believe 51" and my mileage went up almost 1 MPG

cbrahs

is there a baffle in the center of that monster? if so, knock it out. also are you comparing mpg to pre-winter blend fuel? I always loose a couple mpg in the winter.

mikeh1725

I just ordered that muffler, hows does it sound compared to stock?

rammv

My son gave me his Donaldson M085171, I had the 51" on there prior. it is straight through, chamber in the middle. I think it is quieter on the highway than the 51" but deeper and a little louder at idle and excelleration.My egts went up about 25 to 50 degrees but turbo spools much faster,by the lie o meter my mileage went down about 1 mpg but hand calc was up about .5 mpg but also winter blend might have kicked in so mileage might be better. I like the 40" better than the 51" again seems to be a little quiteter and less vibration.

dneilson

I put on the 51 in Donaldson late last summer. Lost 1mpg. Then installed 295/70X18 tires and lost another 1mpg. The winter fuel seems to have contributed another 1mpg loss. Now getting about 16mpg compared to a consistent 19mpg before.