How reliable is the 6.6 gasser?

Doodle · February 19

I think the 6.6 gas is going to be just as reliable as the 6.0 gas in time. I have had a 23 with the 6 speed and now a 24 with the 10 speed. I will say the 24 will pull as much as my 2015 Duramax, it will just get terrible mileage (6-7 mpg). I pulled this trailer the other day and I was grossing 30K total combined. I should have never loaded this heavy but only had to go 25 miles. Pulled the load at 65 no issues other than watching the gas gauge drop. My lifetime mileage with 10K on the 24 is about 12.5. My Duramax has a lifetime of about 14.5 with 130K on it. However it’s actually cheaper to run the gas with the current fuel prices.

I’ve never had any oil consumption issues. Only complaints I really have with my 24 AT4 is it has lots of little dash and interior rattles. Might just be because of the stiffer suspension but it’s kind of disheartening with what we pay for these things.

I would not buy a new diesel again unless I was towing all the time. That’s where diesel shines. I tow seasonally, but heavy. The 6.6 will get the job done but it’s definitely not a diesel as far as torque goes.

I would have to think these new 6.6 gas should easily hit 150K with minimal issues at all. The new 10 speed is butter smooth and a big improvement over the 6 speed in my opinion but the 6 speed was good too.

Dunn · February 26

have not one issue with my 23......works just fine, see no reason to switch and spend thousands for few extra gears

usually the last year before they change are most reliable

bruceb58 · February 27

Just ordered a 24 GMC Denali with 6.6L gas and 10 speed. Thankfully, the 10 speed has been out awhile and its the same one that is mated the the Diesel engine.

Love my 10 Speed in my F150. Reason I waited for the 2024 GMS gas was solely to get the 10 speed.

CRApex · February 27

11 hours ago, bruceb58 said:

Just ordered a 24 GMC Denali with 6.6L gas and 10 speed. Thankfully, the 10 speed has been out awhile and its the same one that is mated the the Diesel engine.

Love my 10 Speed in my F150. Reason I waited for the 2024 GMS gas was solely to get the 10 speed.

20,000 on mine now. You're gonna love the 10spd.

Doodle · February 27

On 2/25/2024 at 9:46 PM, Dunn said:

have not one issue with my 23......works just fine, see no reason to switch and spend thousands for few extra gears

usually the last year before they change are most reliable

The 6 speed is a great transmission as well. I think the 10 speed keeps the 6.6 in the power band a bit better but I had no issues with the 6 speed in my 23. Main reason I traded my 23 for a 24 was I got an AT4 and my 23 was an SLE. I like the looks of the SLE but I hate the fact you can’t get a console and leather seats with the SLE. With the Chevy you can upgrade an LT with those options. I guess as I get older I just want to be more comfortable. Plus I have three kids and there was two cup holders in the whole pickup. Didn’t even have the rear seat flip down.

I honestly think the 6.6 gas will end up being a very reliable engine. I’ve honestly never heard of anyone having any issues with them other than some oil consumption. They have been out 4 years now so there are some with over 100K for sure somewhere. My only complaint is the fuel mileage. I wished it was better but these things also weigh a lot and sit way up in the air. So far the 10 speed is no better than my 6 speed. I was hoping it would be a bit better. It does seem to do better with non ethanol gas. Most of the time I never see any significant difference with my 5.3’s on E10/15 compared to regular but for some reason this 24 seems more sensitive. Problem is E19 vs regular 87 around here is about $0,60-0.70/gal cheaper so it doesn’t really make economic sense to run regular.

Doodle · February 27

11 hours ago, bruceb58 said:

Just ordered a 24 GMC Denali with 6.6L gas and 10 speed. Thankfully, the 10 speed has been out awhile and its the same one that is mated the the Diesel engine.

Love my 10 Speed in my F150. Reason I waited for the 2024 GMS gas was solely to get the 10 speed.

I think this 10 speed is the best transmission I’ve ever had in any vehicle. I have a 15 LML with the 6 speed Allison and it’s fantastic too, but this 10 speed is more refined IMO. Only thing it does sometimes is downshift kind of harshly when coming to a stop. Not all the time, just occasionally. Like it gets confused which gear to drop too. Guess time will tell on reliability but if they put this transmission behind the diesel I can’t imagine any situation where you could hurt this with a gas engine. Just keep an eye on the temps and should last a long time.

BCGM · March 15

there seems to be a whole lot of facts and non facts regarding the 10 speed . I have been trying to get to the bottom of all of it . If some of you know fact from fiction I'm all eyes and ears.

#1 It is not an Allison Transmission , meaning made by Allison . It is Allison branded , GM worked with Allison with consulting on it but it is GM built . ???

#2 Its the same 10 speed as in the Ford transmission . From what I have heard the Ford transmission has different internals and different torque converter ????

#3 The 10 speed transmission paired with the 6.6 gas engine is the same 10 speed paired with the 6.6 Diesel . Not sure about that ???

Please add your comments those of you in the know of facts !

Thank You

vucelick · March 15

#1 true

#2 false, there is a completely different 1/2 ton 10 speed jointly developed with ford and gm.

#3 false. They are the same. However Shift rpm is different due to differing rmp ranges between gas and diesel.

Epsilon Plus · April 11

newdude has confirmed they are not part for part the same. The diesel 10 speed has a few things inside it that have increased strength. Prob cryo shafts or an extra clutch or something. As can be expected of a unit designed to hold twice the amount of torque.

64BAwagon · May 13

Rumor has it that the L8T will soon be making its way into certain 1500 series trucks. Since the 6.2 has proven to have numerous issues it will be removed from availability. No idea what trans though. The trans size may limit the HP/TQ numbers in the 1500.

Grumpy Bear · May 13

56 minutes ago, 64BAwagon said:

Rumor has it that the L8T will soon be making its way into certain 1500 series trucks. Since the 6.2 has proven to have numerous issues it will be removed from availability. No idea what trans though. The trans size may limit the HP/TQ numbers in the 1500.

Now there would be some good news! (If they don't nanny it to death)

KARNUT · May 13

15 minutes ago, Grumpy Bear said:

Now there would be some good news! (If they don't nanny it to death)

The issues are cylinder deactivation related aren’t they? The solution should be easy if it is.

64BAwagon · May 13

28 minutes ago, KARNUT said:

The issues are cylinder deactivation related aren’t they? The solution should be easy if it is.

Thats not what I heard, plus cylinder deactivation isnt going anywhere on that motor (6.2L even though it may get phased out) since GM gets credits from the Govt for using it (which reinforces my long standing opinion that the Govt has more control on what gets built than GM does)

Apparently the Govt already isnt happy about the 6.6 not having it and have pushed for it on the 6.6. Hopefully it stays the way it is rather than ruining another great gasoline V8 with Govt imposed crap.

There seems to be a lot going on behind the scenes.

I cant pin down the changes on the 25 models (I sure hope they fix the lousy dashboard on the Chevy) even though they have run a couple of pilot runs. There is supposed to be a line changeover in July for the 2025 model and beyond that will halt production for a week or so.

Sounds like if youre not a fan of change youre going to be disappointed.

Edited May 13 by 64BAwagon

KARNUT · May 13

9 minutes ago, 64BAwagon said:

Thats not what I heard, plus cylinder deactivation isnt going anywhere on that motor (6.2L even though it may get phased out) since GM gets credits from the Govt for using it (which reinforces my long standing opinion that the Govt has more control on what gets built than GM does)

Apparently the Govt already isnt happy about the 6.6 not having it and have pushed for it on the 6.6. Hopefully it stays the way it is rather than ruining another great gasoline V8 with Govt imposed crap.

There seems to be a lot going on behind the scenes.

I cant pin down the changes on the 25 models (I sure hope they fix the lousy dashboard on the Chevy) even though they have run a couple of pilot runs. There is supposed to be a line changeover in July for the 2025 model and beyond that will halt production for a week or so.

Sounds like if youre not a fan of change youre going to be disappointed.

Some changes I like. Even though I’m a V-8 fan. I still appreciated my wife’s V-6 Genesis smoking several Hemi Challengers including my brothers. I like the cylinder deactivation on my Odyssey. It’s seamless and no one seems to have a problem with it according to their enthusiast website. I like the exhaust sound on my avalanche, it doesn’t make weird noises. The GM 4cylinder peaks my interest as does the Rams new engine. I like reliable performance. I have 4 and 6 cylinder performance vehicles. I don’t buy V-8s to maximize fuel mileage. Performance and sound is the reason. I don’t drive my truck because I want to maximize fuel economy. I like change. The Frankenstein GM V-8 is for their numbers, not the customers.

64BAwagon · May 14

My son has a 1500 SIlverado with the 2.7L Turbomax. he really doesnt do any towing (not that it wouldnt work well) and he feels the 4 cyl is enough motor for a daily driver, he is pretty happy with it. It had a huge impact on the price of the truck.