Hey guys new duramax owner here...just purchased an 05 crewcab 2500hd 4x4...

i tow a 16 foot enclosed haulmark that is about 5000lbs with weight in it...

my question is...

1 the way to my destination this weekend we averaged 8-9 mpg at about 80mph average speed
2 we averaged 12mph on the way home leaving cruise control set at 72mph...and it appears as if unloaded i get close to 20mph at 60mph...

obviously fuel economy appears to be derived off of RPMs on this engine...
our speedlimits in colorado/wyoming are 75 and i would like to tow at 75 as the truck will pull to 95 without a hiccup...

how can i get my mileage up closer to the 15mph or better range while towing...my load is not that big...

will 265 or 285 tires help? bringing the rpms down in the final gear?
will an exhaust help or will that just make me want to floor it more?
do chips really change things on these motors that much.
i dont want to spend too much money on a truck that i would think should do 15 out of the box...maybe it just needs to break in...

anyways any help or advise would be useful...thanks

jason jones;)

Hey guys new duramax owner here...just purchased an 05 crewcab 2500hd 4x4...
i tow a 16 foot enclosed haulmark that is about 5000lbs with weight in it...

my question is...

1 the way to my destination this weekend we averaged 8-9 mpg at about 80mph average speed

Honestly for that speed that's right were it should be

2 we averaged 12mph on the way home leaving cruise control set at 72mph...and it appears as if unloaded i get close to 20mph at 60mph...

Again those numbers are right where they should be

obviously fuel economy appears to be derived off of RPMs on this engine...

You bet-cha right foot = your fuel mileage

our speedlimits in colorado/wyoming are 75 and i would like to tow at 75 as the truck will pull to 95 without a hiccup...
how can i get my mileage up closer to the 15mph or better range while towing...my load is not that big...

will 265 or 285 tires help? bringing the rpms down in the final gear?

A little but taller tires can actually hurt you as it takes more power to get going, unless ALL of your driving is highway going over 285 won't help much

will an exhaust help or will that just make me want to floor it more?

Exhaust will lower your EGT's and possibly get you .5 MPG better, mainly exhaust is for lower EGT's

do chips really change things on these motors that much.

Ummm... in one word YES!!! you'll see (again depending on your right foot) anywhere from 1-2 MPG better with a tuner.

i dont want to spend too much money on a truck that i would think should do 15 out of the box...maybe it just needs to break in...

15MPG towing @ 75 just ain't gonna happen... hate to break that to you

anyways any help or advise would be useful...thanks

jason jones

how can i get my mileage up closer to the 15mph or better range while towing...my load is not that big...


Only tow down long hills. :D

You're probably looking at 11-13mpg depending on your speed. IIRC anything above ~2200 rpms starts to really suck the fuel.

Thank the EPA.

Exhaust may help some. I recommend it since you are towing and it will help lower EGT's. The main thing that will benefit you as far as mileage is the RPM's (speed). If you keep them below 2000 then you get the best benefit as far as mileage especially since you don't tow a heavy load. You probably can get away with 70 mph towing the load you are and get 15mpg on a level surface. You probably don't have 10K miles on it yet? If not you may see some improvement at that point. Also don't go by what the DIC says. Hand calculate your fuel mileage. If it matches what the DIC says then cool beans. Some of the DIC's are right on and others aren't.

Exhaust may help some. I recommend it since you are towing and it will help lower EGT's. The main thing that will benefit you as far as mileage is the RPM's (speed). If you keep them below 2000 then you get the best benefit as far as mileage especially since you don't tow a heavy load. You probably can get away with 70 mph towing the load you are and get 15mpg on a level surface. You probably don't have 10K miles on it yet? If not you may see some improvement at that point. Also don't go by what the DIC says. Hand calculate your fuel mileage. If it matches what the DIC says then cool beans. Some of the DIC's are right on and others aren't.

WE HAND CALCULATED and it was always within .3 gallons of the computer & it was always within .2 mpg of pump numbers vs computer

well these suckers come with 245s dont they? if im only towing less than 10000lbs i wonder if 265s will help just a little...
towing at the speed on our highways to keep under 2000rpms will damn near get you ran over by semis! LOL

ive heard a rumor that after 10,000miles the computer changes and these badboys get meaner...any truth to that?

also the EXHAUST GAS TEMPERATURE lowers with an exhaust you guys say...

what are the options...do people just put biggr mufflers or the entire exhuast or even from the headers all the way to the tailpipe...

what are some good systems that will hold up and not get too loud...i like the engine being quiet...i dont mind a little bit of bark but i want it to be quiet in general when im cruising...

what can i expect to spend for the right systems???

Search the exhaust forum. Plenty of info there.

And FWIW, I doubt the 10k mileage MAP change... Sounds way too advanced for GM.

Search the exhaust forum. Plenty of info there.

And FWIW, I doubt the 10k mileage MAP change... Sounds way too advanced for GM.

LOL yeah well i used to work at a GM dealer and that was what the GM told me...and hes usually not one to tell a lie...but who knows for sure...is the computer GMs or isuzus LOL

...well these suckers come with 245s dont they? if im only towing less than 10000lbs i wonder if 265s will help just a little...

I'm running 265 E rated and @ 70MPH I'm pullin 2100(ish) RPM's. Unloaded I can get 19 to 19.5, if I run 68 (just over 2000) I get 20MPG all hand calc'ed. I've seen as high as 12 or 13MPG pullin 9k so you will see some benefit just not huge. Plus they look MUCH better.

Of course that last statement is only my opinion, I can't provide fact to back that one up ):h

Haulmark trailers often have a tall, flat front. If you can do something to reduce wind resistance, you will see the biggest gains.

Hauling roughly the same weight, with an open car trailer and a low profile car on it, I get about 15mpg at 75mph for extended distances. But with a Haulmark on the back, it got 11.

I didn't know about the 10k rule, but when my 04.5 was over 10k it ran like a different truck. Seems it found some power, I mean really found some power almost scared me and I did all I could to keep it at the speed limit with a whole lot of peddle to go. It was running so sweet I almost did not want to give it up for the 05 DRW I have now, but I did and will wait for the 10k rule to kick in on this one.

Haulmark trailers often have a tall, flat front. If you can do something to reduce wind resistance, you will see the biggest gains.

Hauling roughly the same weight, with an open car trailer and a low profile car on it, I get about 15mpg at 75mph for extended distances. But with a Haulmark on the back, it got 11.

thats good to know...guess its time to buy a new trailer!:ro)

You could just add a "nose cone" to your existing trailer to improve it's aerodynamics (it's the bubble thingy that goes on the front). They aren't cheap - but neither is diesel these days...


- jeff

You could just add a "nose cone" to your existing trailer to improve it's aerodynamics (it's the bubble thingy that goes on the front). They aren't cheap - but neither is diesel these days...


- jeff

THANKS FOR THE TIP i think i would rather just by a new trailer!:ro)

just out of curiousity...

2 questions for those following this post

1...how much does a complete reliable propane injection system cost???

2...ive always had a high regard for banks turbo stuff...is the banks kit that comes with computer and exhaust stuff top quality???? i know its not cheap but its a name ive always trusted long before i even thought of owning a diesel...and i would consider doing that upgrade if it helps towing/fueleconomies...

thanks again for your guys help...im trying to learn all i can here...just ordered up a DVD for the crewcab for the long road trips...and got my windows up front tinted today!:)

80MPH with a trailer!!! hope you have great trailer brakes!

towing at the speed on our highways to keep under 2000rpms will damn near get you ran over by semis! LOL


Those semis are not getting 15mpg @ 65+, try 5 - 6mpg. ):h

Idahofox

I have the duramax in my 32' 2005 Gulfstream Endura, and tow a 23' trailer with my racebikes behind it. Combined weight while wet, I'm about 23,000# and I've easily got 3x the frontal area over you to push the wind. At 67, I get 10mpg on the head.

From my slight experience here (only 3600 miles on the rig so far), the biggest factors are frontal area (how much wind are you pushing) and how fast you're going.

Slow down a bit and you'll gain a lot in mileage... JMHO..