Fuel mileage on 6.6 duramax & 6.6 gas!

Fastrac · October 4, 2020

Wondering what everyone is getting for fuel mileage on there 2020 2500hd with the 6.6 duramax and 6.6 gas. Trying to decide between the two. Coming off a 2017 1500 slt with the 6.2 max tow. Got anywhere from 17- 21 depending on how I drove it. Thanks. Sorry if this has been asked already.

Londart2020 · October 4, 2020

Mostly around town for me, but I get about 15.5 with the Duramax. I had a quick turn around from a 2020 1500 to the 2020 2500. In my 1500 with the 6.2 same driving I was getting about 16-16.5 so for not having to worry about towing my TT I’ll give up 1-1.5mpg. Also when I towed my TT I was getting 7.8mpg with the 1500, now I get 11mpg with the Duramax. Heard nothing good about the 6.6 gas if you will be towing at all.

ShotgunZ71 · October 4, 2020

I tow a 42', 15000lb 5th wheel with my 6.6 GAS High Country. It averages between 7.3 - 7.5 while towing. Pretty decent, honestly. The diesel I had was not quite 2 mpg more while towing a smaller, lighter TT. Unloaded highway mileage is in the mid-teens, around town is low teens, rural driving is upper teens.

SilveradoX2 · October 4, 2020

For similar mileage, consider the cost of diesel. I'm paying 1.69 now in Phoenix. Regular is 2.09, premium for my 6.2 is 2.49. My last trip to Colorado and back I paid the same price as regular once, otherwise always lower. I invest in oil, it's not going up, middle east is pumping harder again and demand isn't going up.

I tow out west up to 11,000, a 6.6 gas motor isn't going to get it done. I'm about to order a 2021 3500 AT4 with a Duramax, for the additional payload. It will get a Banks Derringer for additional power.

Stand By · October 4, 2020

I didn't need a diesel, just a 3/4 ton for pulling the boat which is a bit much for a half ton. Generally an hour each way, sometimes more. Initially I was concerned about the unloaded mileage, but I don't have much of a commute anyway. Was a little jealous of the 6.2 being slightly better, then realized if you add a couple thousand pounds to the half ton to even out their weight, they'd probably be at least the same mileage or the 6.6 slightly better.

deluter · October 6, 2020

On 10/3/2020 at 11:15 PM, Fastrac said:

Wondering what everyone is getting for fuel mileage on there 2020 2500hd with the 6.6 duramax and 6.6 gas. Trying to decide between the two. Coming off a 2017 1500 slt with the 6.2 max tow. Got anywhere from 17- 21 depending on how I drove it. Thanks. Sorry if this has been asked already.

I just completed a 600 mile trip last week and averaged 22-23 MPG but I had a best of 29.9. I am was also running a Derringer on Level 6 the whole trip.

2020 2500 AT4 Duramax

Londart2020 · October 6, 2020

2 hours ago, deluter said:

I just completed a 600 mile trip last week and averaged 22-23 MPG but I had a best of 29.9. I am was also running a Derringer on Level 6 the whole trip.

2020 2500 AT4 Duramax

can you tell me a little more about the Derringer? That’s a Banks thing right? Difficult to install? Worth it do you think? Thanks.

Pate Services · October 7, 2020

I have just under 3,000 miles on my 2020 3500HD with the Duramax. I have a 22 mile commute to work which is mostly back roads and a few traffic lights. My average mileage to and from work is 18-20mpg. My mileage starting at the day I picked up the truck according to my trip odometer is 17.1mpg. My hand calculated mileage is usually about 1mpg less than the dash says. Very impressed with mileage. Keep in mind that my short term mileage will drop drastically when it's in regen.

deluter · October 7, 2020

17 hours ago, Londart2020 said:

can you tell me a little more about the Derringer? That’s a Banks thing right? Difficult to install? Worth it do you think? Thanks.

Very simple to install, through I recommend routing the wires through the door jamb and avoid the firewall. I tried to follow my plow controls but I just couldn't get it through. Be sure to undo both batteries for at least 90 minutes to be sure the computers loose all the drive data... it conflicts sometimes with the derringer when it comes to gear selection relative to throttle position. Power gains are very noticeable and according to the iDash TQ and HP at the ECU readout I have seen 565HP and 991TQ. I am not sure how accurate the readout is as you should be seeing 1050TQ+ but you can definitely feel it. I am still thinking aout a full ECU tune though now that some of the pricing has started to come down, but this was a great way to get some bolt on fun for short money.

BigKahuna · October 14, 2020

First tank I got 18.4 hand calculated, 60% highway 40% city, 634 miles between fills. DIC said 19.4.

Ray Pickle · October 14, 2020

If fuel mileage is your primary decider the choice is obvious, diesel. Cost per mile gas.

GeeManCan · October 15, 2020

My 2020 Sierra 2500HD is about a month old it is a Duramax and not towing on the hwy I am getting 24 mikes to the gallon. For all the KM people tats about 9.8 litres per 100 kms

Dunn · October 18, 2020

I have 6.6 gas and empty in town LA coastal ( live at beach with tight streets and lots of lights and stop signs)....its around 9 mpg

Once I hit freeway its 16-20 mpg unloaded

If you have a ton of stop and go it kills mileage...

In gas version it loves momentum....but stopping every block it hates

ShotgunZ71 · October 18, 2020

19 hours ago, Dunn said:

I have 6.6 gas and empty in town LA coastal ( live at beach with tight streets and lots of lights and stop signs)....its around 9 mpg

Once I hit freeway its 16-20 mpg unloaded

If you have a ton of stop and go it kills mileage...

In gas version it loves momentum....but stopping every block it hates

Yeah, all the HDs love momentum and rolling along. However, the Duramax is just as bad or worse in stop and go. When I had mine and ran short trips stop and go, I thought something was wrong! Lol! Actually, your mileage is probably on par or better than a Duramax in exact same conditions. Having had both, I have found is that the Duramax mileage isn’t much better unless unloaded on the highway. Yes, it’s a couple mpg more when towing, but not as much as when unloaded on a highway. Trade offs either way, and I’ve enjoyed both with each of their strengths and weaknesses.

redwngr · October 19, 2020

On 10/3/2020 at 11:15 PM, Fastrac said:

Wondering what everyone is getting for fuel mileage on there 2020 2500hd with the 6.6 duramax and 6.6 gas. Trying to decide between the two. Coming off a 2017 1500 slt with the 6.2 max tow. Got anywhere from 17- 21 depending on how I drove it. Thanks. Sorry if this has been asked already.

This isn't 2020 vs 2020, but it's 6.6 vs 6.6.

Doing same job, lots of 55 mph commuting.

Not me operating it.

Stole the post from another site.

I went to a gas burner last year and here are the results. I have traded Chevrolet pickups every 14 to 16 months for several years. All have been Duramax engines until last year and I went with the 6.6 gas. I am basing my figures on 36,000 miles a year which is my average. I commute to work about 40 miles each way on rural 2 lane highways, 55 mph speed limit. All of the diesels have averaged over 36,000, 18.3 to 18.4 mpg. I drive a 3/4 ton for carrying capacity as the bed is always loaded with my tool/ service skid which weighs around 2000#. I tow maybe 10% of the time and mostly short trips hauling round bales. The gas 6.6 has gotten 15.3 mpg under the same conditions. So diesel used 1956 gallons while the gas has used 2353 gallons.

There was more info about fuel costs, etc, but fuel prices being a local thing I didn't copy that part.