I have a 2003 Dodge Cummins diesel, 4 door long bed, 2 WD geared for the highway (sorry can't remember the ratio). I have 195,000 miles on this truck.

I typically get 21-22 driving around town in bad traffic. At 65 on the interstate I get 25.5. Hell, at 55 I have gotten almost 30. It has been a great truck.

I just had the oil changed (Rotella 15-40) and had the tires rotated and pressure checked to 50 in fron and 70 in back.

My mileage went from 21.5 to 18. this is the worst mikleage I have ever gotten.

We chacked the air filter, even though I had changed it recently. We checked for a fuel leak. No leaks.

Any ideas why this dramatic change for the worse?

 

when was the last time you changed the fuel filter?

 

yes check filter and injectors. my milage was 500 miles from full, mind you i could have squeezed more but don't like to run my tank that low. suddenly the ghost of dodge caught me and it dropped to 350 miles. turns out all injectors and fuel filter needed doing, thank god for warrenty.

 

How can a dirty fuel filter cause mileage to drop? I am not arguing, I am just inquisitive.

And what do you mean "check the injectors"? Check them how and for what?

 

Anytime mileage or performance starts to lack thats the first thing to check. Majority of the time its the fuel filter. Im sure Drew or Jake will chime in with the "Scientific"(sp) explanation for it.

 

My guess is the tire pressure in the front is too low as well. I have found my tire pressure needs to be 75- to max 80lbs to get the best tire wear and fuel mileage. Hope this helps
My pressure is 80 front 65-70 rear. For best tire wear and fuel mileage

 

Wow...no kidding.

Well, I have pretty much always changed my oil at 4000 miles, so I had my pressure checked regularly, stayed at the 50F and 70R. I got 160,000 miles (and that is no lie) out of the tires that came on it. I am 35k into the 2nd set of Michelins.