379/ISX fuel mileage issues... looking for ideas

What rpms are you running at cruising speed?

 

I'm not familiar with the ISX platform but it sound like you might be below the sweet spot. I would bump it up to 1425 or so and that should up your cruise speed to 63.5mph.

Additionally, the lug design of your drives is killing your fuel economy, a solid shoulder design w/ lugs in the middle is a much more efficient design for fuel economy.

 

Maybe the overhead needs to be run.

 

A flat top truck pulling a reefer is like pulling two trucks down the road. One of those wings on top might help but will hurt in the looks department. Your rpm's are fine mine get's the best mileage at that speed/rpm. Lug tires do kill mileage, try closed shoulder or wide singles. Try slowing to 55.

 

Yeah, that 1350-1375 is not bad depending on load and terrain. When I am running on flatter terrain, even heavy, I go well at 1350-1375. When getting into more challenging terrain, I like to work around 1400-1425.

Along with an overhead, a pressure test of the charge air cooler would be wise. And I have to agree with the choice of tires.... those lug drives are definitely eating into the profits. And not having an air dam on top can really cost as well.

I have an '06 ISX with around 805,000 on it. I generally get a minimum of low to mid 6's in the winter and mid 7's in the summer. I run primarily northern tier of US all the time.

Winter is a terrible time to try and see what average mpg is. We have to buck so much wind all the time as well as the air density is higher and fuel BTU energy is lower.

 

Yep, until then he may try adding some lucas fuel additive. Cleans the injectors up a bit. Any T/S has it. Even auto stores have it I think.