GM’s 6.6L L8T Engine | Common Problems, Complaints, & Reliability

[@donaldbrady7910]

I've got a 2024 Sierra 2500 with the L8T. After 3 months of tracking the MPG, I'm getting an average of 15.7. Mostly city driving and I tow a boat about once or twice a month. I'm pretty happy with that.

[@Icutmetal]

That’s great mileage, especially with a lot of city driving.

[@jimmywu12345]

I am about the same ,2024 Chevy 2500

[@keithhall4009]

I’m getting between 10 and 13 MPG mostly city, in my 2024 3500HD GMC Denali. I have 15,000 miles on it now.

[@8020Media]

D - Thanks for taking the time to share your experience! This will certainly help future viewers.

[@johns8771]

Any issues with it burning oil?

[@marcustellechea]

NICE! I HAVE A 2024 6.6 GAS AND IM AVERAGING AROUND 15MPG ,10K MILES ALREADY AND NO COMPLAINTS! REMINDS ME OF MY 1983 C20 WITH A 454! ABOUT THE SAME POWER! THIS NEW CHEVY IS ONE TUFF TRUCK, SOMEBODY WAS LISTENING ! THANKS FOR THE VIDEO

[@8020Media]

M - Thanks for the feedback! Also, thanks for taking the time to share your experience.

[@mechanicman8687]

I chose the 2025 GMC 2500 AT4 HD Gasser. The best truck I’ve ever been in all my 60 years!! I named her Gretchen because she’s thunder storm grey. She has all the bells and whistles that I wanted

[@8020Media]

M - Haha nice! Thanks for sharing your experience!

[@motomatt6752]

2020 lt8 in a 2500hd Chevy 45,000 miles now. Been pretty happy with the engine pull many trailers. I will say that I do not listen to the oil life monitor I change my oil every 3500 hundred miles no matter what and have seen no oil consumption with mobile one 5w30

[@8020Media]

M - Thanks for sharing your experience! Great idea on oil changes, that's the way to do it.

[@cookingcampingwithdoug4014]

I love mine 2023 2500HD Chevy !! 17.5 + mpg average I change my oil every 5000 miles and no oil consumption at all

[@8020Media]

C - Thanks for taking the time to share your experience!

[@clintpeterson9028]

@@8020Media i lost lifter but didn’t have oil consumption

[@brucecollins8865]

My ‘22 L8T has been great at 60k miles. I change the oil at 5k and have zero oil consumption. The 6l90 in the 20-23 trucks is also darn reliable, but the 10 speed has seen valve body failures with long backorder times. As for MPG, I average 16 on my 20 mile one way commute, have seen 17.8 on a 750 mile one way trip, and 10 or so when hooked to anything that resembles a trailer. I ran the numbers and even if the Duramax returned significantly better fuel economy it doesn’t pencil out until 300k miles.

[@8020Media]

B - Thanks for taking the time to share your experience and share these insights!

[@braddurham3015]

The 8.1 ate oil too owned one and I miss it

[@8020Media]

B - True.

[@daniellibich1376]

As the VORTEC 8100 consumed oil as many have guidelines of how much oil the modern BBC consumed as if a liter in 800 kms is concerning. As many know the 6.6 GDI is available as an option in the express/Savana along with the HD lineup as many know its that simple to maintain without AFM/DFM.

[@kellyriley7918]

I miss mine a lot..had a 2004 avalanche 8.1 , didn't eat much oil at all surprisingly. But got a 2013 6.2 in 2017, no AFM/DGM crap on it so I'm happy with that as well but wish I would have also kept the 8.1. First person that looked at it bought it.

[@MIIIB]

Got a 24' custom 20K miles and zero problems. No oil consumption. New engines require proper breaking time. I have friends who first day out of the dealership, and they towed 8K lbs. Meanwhile, I like to change oil at 500, 2,500, and 5,000 miles. There is no towing until 2K miles, so the piston rings and all engine breaks gradually, and the rings sit correctly. I do construction full with 6.6 around, and guess who gets oil consumption 'for life' ? Yes, the same guy who didn't break the engine. They are the negligent people who complain in most cases. Direct injection. No fan, honestly, but catch can with each 2K miles checking the level oil, and you are good. This will prolong the cake valves No AFM, No start up, no DFM, just plain old school technology with old school efficiency, gas drinkers. This is absolutely not impressive for those who know 90s and early00s gas engines. The big boys.in the block. 90/00s $25K trucks are the same value with inflation adjustment as today is $50-60K. The problem is they don't give the same quality, just the same price. This L8T will pass as 1 of the best motors made by GM. Iron engine 2 valve. The magic formula. I'm in shock watching 1/2 truck 30% to 40% higher price as a 3/4s ton and less reliable.

[@8020Media]

M - Couldn't agree more. Thanks for taking the time to share these insights!

[@alicelouisealtstatt3351]

Such excellent advice - I'm just about to buy a Chevy 2500 HD with this engine, and happy to be reminded about proper break in and oil changes. Allison transmission is the clincher. Thank you.

[@matthewanderson9912]

I got a 2022 with 55,000 miles. I bought it new. To this point I’ve had no issues. No oil usage. It’s just been dead reliable. I change oil at 3000 miles. It’s a daily driver/race car hauler. It’s drove literally just about every day. I average around 14 mpg on my 30 mile round trip work commute. I’ve gotten 17 on a trip. And I get 8 mpg towing my 8.5’x24’ enclosed car trailer. No complaints from me.

[@8020Media]

M - Thanks for taking the time to share your experience!

[@joedimsdale3568]

Got a 2022 model with 20000 miles, 16.4 mpg. Been good so far.

[@8020Media]

J - Thanks for taking the time to share your experience!

[@Fljeff7]

Check oil at every fuel fill up like you should. 5k oil service, wet solvent intake cleaning once a year or whenever you change air filter. It's a big engine in a big truck wrong vechile if you want fuel mileage. Nice to see no afm , I didn't work in the early 80s (didn't they learn) and still don't work now

[@8020Media]

F - Couldn't agree more! Thanks for sharing your experience.

[@Fljeff7]

​@8020Media great channel I just subscribed

[@8020Media]

F - Thanks for the support!

[@robertrice4441]

Would using a fuel injector cleaner regularly like the chevron product limit the fuel injection problem?

[@8020Media]

R - It would, just wouldn't overuse it.

[@kevinmeyers3337]

Love mine so far 24 3500 srw avg 12 mpg city driving,seems to do pretty good on highway if keep it under 65 also for a 1 ton.

[@8020Media]

K - Thanks for taking the time to share your experience!

[@arie_lovexi]

i do have a question, would it be a good idea (even tho these are okay engines) to bulletproof these? like changing mufflers and etc?

[@8020Media]

A - It's never a bad idea.

[@scottymoondogjakubin4766]

I suspect the direct injection is causing a fuel/oil dilution prob ! Maybe try at least a 5w30 pennzoil platinum ! Maybe even seat the rings like my grandfather and my dad used to do ! It only takes about 10- 15 minutes

[@8020Media]

S - Great suggestion. Thanks for sharing!

[@musclecars92]

I have a Camaro SS with a 6.2 l LT1 V8 engine. Which also features direct injection. However, I haven't seen any issues. With carbon build up as of yet. General motors design this engine with a catch can from the factory.

[@8020Media]

M - Nice! Thanks for sharing.

[@kellyriley7918]

I have a 2013 Silverado with the 6.2 no dfm/AFM thank God! 98k no oil usage to speak of or anything else and I tow my 2 horses at least 2x a month.

[@musclecars92]

@kellyriley7918 That engine is very similar to the 6.2l LT1 performance engine that they put into camaros..And corvettes. You're lucky your engine doesn't have the AFM That technology has been known to cause problems with the lifters

[@kellyriley7918]

@@musclecars92 oh I know I knew all about it and yeah I knew it was the vette and the Camaro engine, I'm kind of a gearhead and I've had lots of hot rods and muscle cars.. so when I went looking I knew what I was looking for especially considering I was giving up an 8.1 liter Chevy

[@chadmiller6487]

My 2023 gmc 3500 drw l8t has 80k on it and hasnt had a single issue. Besides the paint being trash and doing the regular 5k service.

[@8020Media]

C - Thanks for taking the time to share your experience!

[@Back_door_bandit_98]

I also have a DRW L8T but in a 2020 Silverado crew cab long bed 4x4 cranked torsion bars with 35x12.50s getting 12.5mpg average 73k miles on the odometer what kinda mpg are you seeing?

[@HowardJones-j7c]

Given the choice between the 6.6 Duramax diesel engine and the L8T 6.6 gasoline engine, I'd choose the gasoline version. Not only because I wouldn't work a diesel hard enough, but I'm more used to gasoline.

[@8020Media]

H - Thanks for sharing your opinion. We actually have a video that breaks this down: kzbin.info/www/bejne/pIubaZ2smN6BfdU

[@captainsoftheazulcarrib7491]

Thx for the info!

[@8020Media]

C - Thanks for the feedback! Hope it helps.

[@alsch8436]

Thanks for the positive feedback on the 6.6 gasser! I've seen lots of videos about bad things with the 6.2 and DuroMax but 6.6 gasser comments have been rare. Maybe that is because it has been a GMC Winner! I have a 2020 Sierra dually, 8' bed and bought it to haul a 4,000 lb truck camper. 90% of its 27,000 miles has been with the camper attached. A cross country trip of 7,500 miles averaged 8.5mpg that I am happy with. 401 HP has proven to be more than enough for this setup. I have a real winner here! I love this truck and the 6.6 gasser that powers it. If you find this engine, buy it! You won't regret the purchase.

[@clintpeterson9028]

Ive got 6.6 gas lost lifter

[@8020Media]

C - Thanks for sharing.

[@8020Media]

A - Well said! Thanks for taking the time to share your experience.

[@clintpeterson9028]

@ we need to let people know

[@Intwodeep902]

My 2024 2500hd gas just started leaking transmission fluid going back to the dealership!!!!!🤯🤯🤯

[@8020Media]

M - Oh no.. sorry to hear! How many miles does it have?

[@Intwodeep902]

@@8020Media less 10k

[@8020Media]

M - Keep us updated!

[@Intwodeep902]

@@8020Media just got my truck back. They advised me that it appears that my truck and another one has had the same issue with the transmission fluid was overfilled at the factory or it expanded when it heats up and pushed through the seals they will inspect it on the next oil change so we shall see.

[@8020Media]

M - Interesting. Thanks for sharing your experience!

[@fattie2550]

Install oil catch can and let her rip.

[@8020Media]

F - Not a terrible idea!

[@Back_door_bandit_98]

2020 6.6 L8T Silverado 3500 dually CCLB 4x4 3 inch level with 35x12.50s 2 inch front wheel spacers 3 inch spacers on rear 2 inch spacers between duals I average 12.5 it’s a daily with mild towing when I do tow my travel trailer (10k)(36ft) I get 10 mpg and when I tow the gooseneck anywhere from 14k-18k I get 8-9 73k trouble free miles truck consumes 1qt of oil every 4k mile intervals doesn’t matter what brand oil you run in it so I’m sticking with pennzoil platinum switching to the high mileage full synthetic this next oil change I also have a catch can on the truck bought off Amazon 6L90 is holding up great changed the fluid at 70k along with all other fluids truck really didn’t need it but I plan on paying it off and keeping it.

[@8020Media]

B - Thanks for taking the time to share your experience!

[@codythorpe7700]

2025 2500hd 1387 miles transmission is being replaced this is all the warning you need

[@8020Media]

C - Sorry to hear this.. However, thanks for sharing your experience!

[@jimmywu12345]

👍love my 2024 Chevy 2500

[@8020Media]

J - Thanks for sharing!

[@Connor4x4]

Less oil consumption if you run 0w40, 5w40, or 10w40. Depending on climate. As long as the oil meets API "SP" specifications.

[@8020Media]

C - Thanks for sharing this insight!

[@Back_door_bandit_98]

How long have you run the other oil in your 6.6 L8T? I’m curious because I’ve been thinking about switching to see if it will help my oil consumption.

[@Connor4x4]

@@Back_door_bandit_98 we have one at work that we've been running 0w40 in since the first oil change. About 100k, no issues.

[@iked4421]

Unless you’re pulling very heavy loads consistently, or pull/use your truck for commercial use a diesel is absolutely not necessary

[@8020Media]

I - True.

[@iwoww562a9]

So this will be more reliable than the 1500 6.2? Anyone?

[@8020Media]

I - All comes down to maintenance. We would put the L8T ahead of the 6.2.

[@iwoww562a9]

Damn!!!!! U just made my purchasing decision harder!!!! I was originally going to go with the 2025 1500 6.2​ but no investigating that a 2500 costaboutthe same as the 1500 and ita nore reliable has me considering it over the 1500. Even tho i dont tow anything, i just love trucks. @8020Media

[@iwoww562a9]

​@8020Media I was considering the 6.2 1500. I dont ever tow but want a reliable truck. And the 6.2 seem to have so many issues

[@GrandPitoVic]

The oil use seems to be all new engine. The piston rings are so thin.

[@8020Media]

G - Unfortunately.

[@jordanrobillard653]

We have these for work trucks roughly 100 of them and most of them go through 1qt per thousand miles

[@8020Media]

J - Wow! That's quite the fleet. Thanks for taking the time to share your experience!

[@toddjohnson7787]

Just grab a reliable UPR catch can for the direct injection issues with this engine and it’ll save you from having to walnut blast the carbon deposits off the intake valves. So I’d rather pay $200 now than pay $1k later. You have to treat these engines as an investment and take good care of them. Especially the ones without major lifter issues. 👀

[@8020Media]

T - Well said!

[@Intwodeep902]

What some examples to boost the horsepower a plug and played tuner in a bold on do you have a video on this?

[@8020Media]

W - We don't currently have a video on this, but we will shortly! For the time being, we have an article that may help from our website: chevytrucks.org/l8t-performance-upgrades/

[@Icutmetal]

@@Intwodeep902 You’ll spend a lot of money for very little net gain on a N/A engine. There’s no magic formula.

[@Intwodeep902]

Wow, thank you so much! I used to have an incredible plug-and-play tuner from Superchips for my 2005 GMC Sierra 5.3L, and let me tell you, that thing was a game-changer! I'm eagerly waiting for Diablo to release a tuner for the 2024 2500 HDs, or really any plug-and-play option that caters to the 2024 2500 HD gas engines. I'm seriously pumped about the idea of diving into E85 octane-especially if there's a video showing how to make it work! Can't wait to see what’s coming next!

[@Intwodeep902]

@ man I’m super excited with my 2024 2500 HD 6.6 L gas burner just for it to be stock. That thing will get up and go and it will pull my campground boat with no problem at all. It already has a factory built-in ram air intake.

[@Icutmetal]

@ No it does not.

[@jgmullins1]

Give me this motor in a 1500 series frame and you have a buyer.

[@8020Media]

J - Haha if only!

[@heinzletzte.6385]

As a european watching this I wonder why US companies arent putting a low hp small displacement diesel in it like a 2 or 3l inline. For people who just want to drive around without towing much and without terrible mileage and reliability. In europe pickup trucks are moslty in the Ford Ranger size range but everyone offers a diesel. So if you want a reliable vehicle get the 150hp diesel, delete it and only change the oil for maintenance.

[@DFitz-bk7dj]

I really wish GM would get rid of the Direct injection and go back to port!!

[@GrumblesM4]

I like mine more than I like my c8.

[@8020Media]

G - Wow! Thanks for sharing your first hand experience.

[@jerrydosser7031]

Saying this is their best is actually not saying much.

[@8020Media]

J - Okay.

[@danthompson1467]

Oil burning is not rare

[@8020Media]

D - Thanks for the insight!

[@davisfamilyshenanigans4807]

I love mine but I burn a qt per 4000 miles

[@8020Media]

D - Thanks for taking the time to share your experience!

[@JohnDiMartino]

We have 3 2022s at work they all use oil ,need to add oil 2x per 3-4000 mile oil change intervals . Much prefer our older 6.0 engines, held 6 quarts and use no oil even the older ones with 13,000 engine hours , these L8Ts hold 8 and use 4 more so literally costs us double to operate these from an oil change perspective. I’m going thru my drums of 5w30 Dexos a lot faster since we got these trucks . GDI was a big mistake on HD trucks

[@8020Media]

J - We completely agree.. Thanks for taking the time to share your first-hand experience!

[@dixienormous9052]

I have the 6.2 10 speed 2019 1500 high country The best I’ve gotten on freeway driving 25 mpg PDX to Salem and back This engine is bad ass to say the least I tow a 8K travel trailer with it to Average around 9 to 10 mpg Except into the wind then 7 mpg Best I’ve gotten is 13 mpg with trailer

[@Icutmetal]

I think you have the wrong video.

[@keithhall4009]

yep, wrong truck and wrong engine. This is an HD Truck and engine.

[@8020Media]

D - Thanks for sharing your experience on the 6.2.

[@monster7649]

The oil life monitor uses rpm & cycles to determine % with a max set at 7,500miles under perfect conditions

[@monster7649]

Also forgot to mention the l8t is the only cast iron block gen v & the only gen v without afm aside from the lt5

[@8020Media]

M - Thanks for sharing, but we still wouldn't advise following it honestly..

[@High61Way]

[@8020Media]

H - Thanks for the feedback! Hope it helps.

[@High61Way]

@@8020Media 14-15 mpg w L8T V8 .2024 2500 LT use ethanol free gasoline at WAWA it's also 89 octane .truck is well engineered ,imho .....

[@Rodeo32145]

Actually the duramax is 10,000 plus the l8t engine.

[@8020Media]

R - We said an extra $10k?

[@BigBenny24]

I would not reccomend any GM vehicles until the investigation is complete of whats causing multiple models engines to fail.

[@8020Media]

A lot of it is the DFM systems on the half-ton V8 engines unfortunately

[@michaelfrohn255]

Just more destruction of the cam! I used to love GM! But I gave up on them now, absolute garbage! Frame Rott, fuel line rott, brake failure! Lifters failing and destroying the camshaft aka engine replacement!!! And the common transmission replacement’s !! Designed to suck your bank account dry!!

[@8020Media]

M - Sounds like you have some anger towards GM. Sorry to hear. We can admit they don't make them like they used to.

[@KathyHarris-v5u]

Yeah direct injection 😢

[@8020Media]

K - Unfortunately, a lot of manufacturers are doing it nowadays.

[@donstein475]

Just sick of this new junk.

[@Icutmetal]

Thanks for letting us know.

[@ada-yw1bb]

Don't buy one then .

[@8020Media]

D - They don't make them like they used to, but unfortunately, it's not likely to change.

[@anthonyanderson464]

The EPA has about killed Diesel engines, and gas v8 are next on the list.

[@mickwells4714]

You didn't watch the video he's not saying the 6.6 is junk Move along you woke goof

[@dillonpieper5517]

Wouldnt have half the problems of any of these new engines if they wernt direct injection.

[@8020Media]

D - Well said..

[@kennethdudkowski688]

You got all these want a be truck owners making it's junk comments they need more tech inside smother ride probably are just want a be truck owners little pavement lovers and don't know shit only repeat crap they hear on line

[@8020Media]

K - Are you talking about us?

[@paulradice3534]

Slug motor offer the 6.2

[@8020Media]

P - What?

[@johnwest2396]

Junk

[@8020Media]

J - Wouldn't call these junk... But, they certainly don't make them like they used to.

[@bluesky-ud9wg]

Best, haha, that's hilarious. The Duramax is the weakest, the 6.6 gas is also the weakest. Like anyone pulls with either

[@chadmiller6487]

I have the 6.6 gas in my 2023 3500 dually. 80k on the engine and it's married to a gooseneck 6 days a week.

[@bluesky-ud9wg]

@chadmiller6487 That's nice, you have to look at the whole industry not just 1 example. I had a buddy long ago with a Dodge Intrepid. He hardly changed the oil let alone actually maintain the car. It had over 140,000 miles and actually ran great. That doesn't mean they are good cars. Again, who uses a GM to pull anything. All you see are Dodge & Ford pulling cars & hot shot

[@Frawl099]

@@chadmiller6487what kind of mileage do you get when towing?

[@ada-yw1bb]

​@@bluesky-ud9wg: Go back to ur moms basement.

[@Icutmetal]

@@bluesky-ud9wg Nice troll.