2006 Dmax Performance

That is about what I'd expect, given your stated driving conditions.

My '06 DMax was in the 14-15 mpg range on my 10 mile commute, which was about 50/50 city/freeway.

I loved my Dmax, but the fuel economy never quite met my expectations.

As others have said - you are expecting too much for the short trips.
My 2005 gives me 20+ on the highway, 12+ towing but is a pig on fuel on short trips around town when it does not even warm up.

I get miserable mileage on my diesel until it reaches operating temperature. On a cold morning it will get about 3-6 mpg. Once it warms up I get 17-18 in town. It typically takes 10-15 miles to reach operating temperature when the outside temperature is in the 60s.

You may need new thermostats. A typical problem is the o ring leaks on the thermostats which will not allow the engine to reach operating temperature.

Dmax thermostat

What is the engine temp after a 15 minute drive?

My 05 GMC Sierra with a 5.3L got me 13 to 14 MPG on the same driving. I will be only driving the short distance for a couple of months. I will be retiring soon. The truck is from Texas so it was set up for Texas smog. It should get better then California equip truck.

Your 3 miles each way probably has lots of stops and starts..(red lights, etc). This type of driving is a HUGE mileage killer for any vehicle.

I have a 2006 Duramax with the LBZ engine and have had it since new. I typically get 15-16 with all in town driving and 19-20 on the highway not towing. Towing a 14,000 fifth wheel I typically get 12 +/- .5 mpg.

Are you basing your mileage on the computer read out? If so that is your problem. I have noticed that when you start many times for just trips the computer information can not be trusted. It gets a little bit lower with each start it seems. I have no idea why since I didn't design it, but I can tell you that if you fill up, drive only very short trips your mileage will show very low. If you then put it on the highway without resetting the computer or filling up you will see the mileage start to increase with each mile. It will never get up to highway mileage without a reset due to it being an average since the last reset.

If you only drive 6 miles per day, fuel costs should not be important. No internal combustion engine likes 3 mile trips.

We have a 2006 Duramax, had it since it was new. I can get 20 MPG on the highway at 60 MPH. From our home to town is ten miles, and trips to town and back, with city driving I get around 16-17 MPG.

Don't idle the engine to warm it up, that will kill your mileage. Just go easy on the fuel lever until the engine starts to warm up, which it won't in thee miles. I think that will be a problem.

mtofell1 wrote:
3 mile trips back and forth to work are not going to get good mileage in a Prius. It's a 7500# truck. 11mpg is good for the conditions your describe. Take it out on the highway and drive it and you'll see good mileage. I drove that exact truck for 125k miles in all kinds of conditions with and w/o trailers. Short trips in the city 11 sounds about right. Highway keeping your foot out of it you can get in the upper teens or even 20 if it's flat, no wind and you keep it at 55. Mixed hwy/city driving moderate I got around 15 for many many miles. Short trips and starts/stops kill mpg with any vehicle but it's especially hard on big trucks. It's not easy moving 4 tons from a dead stop.

This is spot in with my Duramax experience as well.