Mileage Help!

[holleta]

2006 LBZ, Allison Crew Cab 3500 Dually, 4:10 gears 4x4-all stock. Wifes truck, pulls a 14k 5th wheel horse trailer EXTREMELY WELL- no complaints there. Mileage seems low, especially when empty. 8-11 mpg when towning ( I'm thinking not bad, most in hilly PA.) Empty is 12.7 average rural and highway, this seems low compared to other diesels we own/owned and most other folks reports.

Truck performs great-no complaints, towing is 50% of the time now. Not sure if my expectations for mileage are too high or I have an issue.

Any advive appreciated.

 

[Unit453]

12 is low for unloaded mileage.

Couple things:

First, welcome to the site...!

Second, when is the last time you changed your air filter? Thats the most commonly overlooked piece of maintenance. They can glog up and look completely fine. Try pulling it out and bang it on the ground and see if all kinds of crap comes out. You should be able to blow through it and feel a ton of air through the other side.

Second, you might be due for a fuel filter change. Many people notice a drop in mileage when their filters get dirty.

Third, I'm sure you're running winter blend fuel up there by now and having #2 cut with kerosene will kill your mileage for sure due to less BTU's.

Fourth, there are some simple upgrades you could do to open it up a bit and help it breath a lot easier. You could pop the "fin" out of your stock air box letting it breathe easier. You could always get an inexpensive programmer to boost your mileage too. With that dually, you should be getting 15-18 unloaded.

The problem with these trucks is that none of them are the same. Some get 24 mpg out of the box and others are getting 12. There's no rhyme or reason why either.

Air box "air foil":

 

[Unit453]

What you want to do is tear out your stock intake. Remove your filter from the air box. Then find the very end piece with the rubber seal attached to it. You can pop that off. Its clipped on to the air box and is designed to seal off the intake from underhood air, which is hot and not beneficial to the motor. Get something and cut the fins out of the circular end piece. What you'll have left is a plastic ring with a rubber seal still on it. Then just put your intake back in the truck.

 

[THEFERMANATOR]

Also if it's stock it's got 3.73 gears in it, not 4.10's.

 

[Unit453]

I thought duallies had 4:10's....(?)

 

[SfcJones]

I thought duallies had 4:10's....(?)

Me too.....

 

[THEFERMANATOR]

Nope, ALL DURAMAX's in the GMT-800 platform have 3.73's. My donor truck is a dually and it definately has 3.73's in it.

 

[holleta]

Thanks for the welcome! Took out the fan looking thing, fuel filter is fresh, air filter is semi fresh. Mileage still @ 12.7 empty. Mileage seemed to always be this way...80k now. Pulls better than all the diesels that came before so I'm not complaining...just wish the mileage was a bit better.

 

[CtChevy427]

Is that mileage hand calculated?

 

[Ed HD]

Is that mileage hand calculated?

X2, DIC's are only estimations. I've never had my DIC within .3 mpg of actual mileage. This is on my Bonneville, but it's the same deal with the D-max trucks. Mileage driven/gallons used is the most accurate way. It also helps if you use the same pump at the same station, to the same level, to eliminate variables in the pump itself.

 

[Unit453]

Have you put on larger tires?

 

[holleta]

The mileage is a mixture of both hand calc and overhead, they are usually within 1 mpg or so and that's close enough for me. Stock size tires, mileage has always been poor compared to past and present trucks but the pulling power has been phenominal.