I wanting to know during the break in period of a new ctd does the mpg go up and down. The reason i ask is because when i got my new diesel it was getting great mileage but it now seems to be getting worse, and i always hear the it gets better after break in. So is this normal.

 

No. That is not normal. You should be getting better mileage,& power as the engine breakes in.Are you running it hard to seat the rings? Hook up a trailer,or put some weight in it,& drag it over a few mountain passes for a while to get it started.

 

Are you calculating your mileage by hand or just watching the overhead? If you are just watching your overhead display and never reset it it will go down. Hand calculate a few tanks to double check.

 

well i have done both types of calculations while reseting the overhead and it pretty much matched up. i have also hooked up both a rv and a boat.

 

Well you don’t state how many miles are on your truck. Do you live where it gets cold so that in the wintertime they sell winter fuel? You may need to change your fuel filter if you have over 10,000 miles. If under 10K you could of gotten some dirty fuel or even bad fuel! If you drive a lot in stop and go traffic and very little on the hwy to heat the engine up you may be getting carbon built up on the injector tips. The above is just a few ideas to think about as they may or may not relate to your problem.

 

check your air filter to changed mine at 6k and it was already dirty enough to hurt mpg cahanged it and picked up almost a mile per gallon

 

Mine actually did the same...around 4000 miles, i got great mileage, then around 7-9000, it dropped about 3 mpg and hung out there...im now at 17000 and it went back up about 2 mpg.

 

This wonderful new ULSD can cause you issue also. I lost 1 MPG when I had to start using ULSD because that is all I could find.