Carrier Bearing & MPG

In the past 2 years the gas mileage on my 2002 3.4 has been declining from about 17 MPG to 15 MPG. I keep it maintained, tuned, tire pressure, etc.

About 4 months ago I noticed a strange "chirping" noise only when decelerating. Couldn't figure out where it was coming from. To me it sounded like left front, passenger said right front. rear passengers said under them.
It took 3 trips to the dealer to figure out that my drive shaft carrier bearing was bad.

Now that it is fixed my MPG is back up to around 17 and the truck just seems to run better now. Is it possible that the bearing had been going bad for 2 years (undetected until I heard the chirping noise) affecting gas mileage?

 

Seems unlikely. Usually you get some sort of driveline vibration as the rubber support around the bearing wears out and the driveshaft wobbles around, I'm surprised you didn't feel anything like that.

 

Dealer said there was a vibration past 65 MPH. I never really felt it.

 

Man those 1st gens look good. On topic with your post I noticed maybe a month ago my mpg dropped maybe 1-2 per tank (could be my low tolerance for dumb ass south Florida drivers). Fast forward to about a week ago I noticed a u-joint type squeak while driving past a wall & already knew my carrier bearing needed replacing. This post makes me wonder if those contributed to my mpg change. I'll post back in about 3-5 fill-ups (I use Fuelly app) to see if there is a return to my usual mpg after u-joint/bearing replacement.