Jump to content

6.6 Direct Injection Reliability Concerns

Khoa Pham

By Khoa Pham
in 6.6L Gas V8 (L8T)

 Share

Recommended Posts

Khoa Pham New Member

Khoa Pham

Posted
Posted

Hello Friends,

 

My dad is in the market for a new 2500 Express van since his 2014 Express with the 4.8L V8 gave out at only 130,000 miles. Naturally, I wanted to find him a 2020 van with the 6.0L V8 but he is drifting towards the newer 6.6 gas. 

 

For 2021, Chevy did put the 6.6 L8T motor into their 2500/3500 Express Vans. I am sure that this powertrain combo is the same as the HD Silverado pickups.

 

Since I am unable to find much information about this motor, does anyone know what sort of engineering GM has done to prevent carbon buildup on the intake valves? This is an issue with DI motors and I am concerned with longevity and increased maintenance costs if one has to take their truck in every 30,000 miles to have the carbon buildup sandblasted. 

 

If Toyota decided that adding both port and direct injection to their motors would resolve this issue, what sort of magic did GM come up with?

 

 

  • Replies 40
  • Created
  • Last Reply

Top Posters In This Topic

Popular Days

Top Posters In This Topic

Popular Days

Popular Posts

Grumpy Bear
Grumpy Bear

Fuel additives not only clean valve backsides in SPFI or carburetor motors but help keep the carbon neutral balance in the combustion chamber of al SI motors. The injector now in the combustion chambe

Pryme
Pryme

It’s unlikely I’ll go over 4k miles on oil in my truck just due to the lower miles I’ll drive it. Hopefully that will help a bit.    my short trips and cold climate already puts me in severe us

Grumpy Bear
Grumpy Bear

Blow-by gas is an interesting subject. Observations for what they are worth. All ventilation systems move gas by pressure differential. Manifold vacuum is the driver and until rings expire will be the

Posted Images

spm1us Enthusiast

spm1us

Posted
Posted

From what I have researched it appears that reducing the oil change interval has a dramatic effect on the quantity of carbon deposits. I plan on using Shell Gas and Truck 5W30 oil and Baldwin B7449 filters on a 4500-5000 mile OCI. The use of a GM Dexos 2 approved oil would also keep your warranty in effect. GM has also designed the valve covers to catch the oil vapor that contributes to creating these deposits. Some owners are also installing Catch Cans to trap the oil vapor. With Direct injection, there is no longer any fuel wash to keep the intake valve clean. 

-David- Enthusiast

-David-

Posted
Posted

I am a prospect buyer and am also very interested in this subject.  I like to keep vehicles for a really long time.  As of now I have not see anyone show borescope photos or any other evidence of how well these engines mitigate the buildup over time or miles or if they suffer from fuel dilution in the engine oil.  A recent thread showed a catch can installed that was collecting oil/water mixture in the 6.6 which shows that the OEM separator is not 100%.  Fuel type (top tier), oil type, oil change intervals, type of usage, etc. are all contributors.  In general I do not like the idea of adding catch can in that the water/moisture caught can freeze and *might* inhibit gas flow of which can cause other issues.  It surprises me that GM will not run a port and GDI system like Toyota and Ford are now using in lieu of straight GDI.

Khoa Pham New Member

Khoa Pham

Posted
  • Author
Posted
On 1/24/2021 at 9:28 AM, -David- said:

I am a prospect buyer and am also very interested in this subject.  I like to keep vehicles for a really long time.  As of now I have not see anyone show borescope photos or any other evidence of how well these engines mitigate the buildup over time or miles or if they suffer from fuel dilution in the engine oil.  A recent thread showed a catch can installed that was collecting oil/water mixture in the 6.6 which shows that the OEM separator is not 100%.  Fuel type (top tier), oil type, oil change intervals, type of usage, etc. are all contributors.  In general I do not like the idea of adding catch can in that the water/moisture caught can freeze and *might* inhibit gas flow of which can cause other issues.  It surprises me that GM will not run a port and GDI system like Toyota and Ford are now using in lieu of straight GDI.

Agreed! Would love to see how these hold up since the Chevy promo videos are so proud of having the first DI motor in the HD segment. I have my doubts since the engineers made questionable choices on the new 3.0 duramax too. 

CamGTP Senior Enthusiast

CamGTP

Posted
Posted

If the engine ran long enough moisture is not a concern to have. I have 109,000 miles on my DI 5.3 engine, I took pictures of my valves at 104,000 miles and have zero concerns with them at that mileage. There is a thread on it I made.

 

As a previous post said, they make cleaners that anyone can use. If you are that concerned you can buy a can of cleaner and run it through the intake every 20-30k miles just to make you feel better.

  • 2 weeks later...
Carl Brothers New Member

Carl Brothers

Posted
Posted

I've ordered a 2021 Sierra 2500 HD with the 6.6 liter  GDI motor. It'll be here around Feb. 27th. Don't know how well it'll work, but, I'm installing a water injector set up between the MAFS in the air inlet tube and hat on the intake manifold. I used to run water injectors back in the late 70's and 80's and aside from letting me get away with running street gas in a high compression engines, it also kept the cylinder heads and piston tops totally carbon free after many miles between teardowns to fresh these motors up with new rings and bearings.  Still not sure if it'll help with carbon build up on backside of intake valves, but, I'm going to give it a shot. 

HondaHawkGT Senior Enthusiast

HondaHawkGT

Posted
Posted
On 1/24/2021 at 9:28 AM, -David- said:

I am a prospect buyer and am also very interested in this subject.  I like to keep vehicles for a really long time.  As of now I have not see anyone show borescope photos or any other evidence of how well these engines mitigate the buildup over time or miles or if they suffer from fuel dilution in the engine oil.  A recent thread showed a catch can installed that was collecting oil/water mixture in the 6.6 which shows that the OEM separator is not 100%.  Fuel type (top tier), oil type, oil change intervals, type of usage, etc. are all contributors.  In general I do not like the idea of adding catch can in that the water/moisture caught can freeze and *might* inhibit gas flow of which can cause other issues.  It surprises me that GM will not run a port and GDI system like Toyota and Ford are now using in lieu of straight GDI.

 

Catch cans will mostly capture water and a tiny amount of oil/combustion byproducts. Mine would freeze solid in the winter and it was extremely annoying. If I didn't drain it every 2 or 3 days, it would be so full of ice that it blocked path between the intake and PCV. IMO, if you live in a region that's cold, catch cans are waaay more of a hassle than they're worth. I'm thankful I didn't damage any seals driving around with blocked off PCV system. 

 

If intake buildup is really that big of a concern, a PCV delete setup would be a better way to go. Plenty of sports car guys do it. Auto manufacturers would do it, but the government doesn't look kindly venting crankcase gases to atmosphere.

  • 2 years later...
rileyc Enthusiast

rileyc

Posted
Posted

I recently took delivery of a 2023 Chevy Silverado 3500HD with a 6.6L L8T gas engine after waiting 10 months from the start of order to delivery.  A concern I have with the L8T is the build up of intake valve deposits.  I have read that GM has an extension baffle system in the valve covers to mitigate the issue.  I also have read about owners installing catch cans as a preventative measure.  Additionally, many owners are doing shorter OCIs with the appropriate Dexos1 Gen 2 or Gen 3 oil and/or using top tier gasoline to help minimize intake valve deposits. 

 

Since the L8T is only a few years old, I have not seen any borescope photos of the intake valves.  Does anyone with the L8T have any actual data on intake valve deposits for this engine?  

Dr1ft3r Enthusiast

Dr1ft3r

Posted
Posted

Use top tier fuels and run cleaner through it every now and then.

I am using this every 6,000 miles:
https://www.amazon.com/Chevron-Techron-Concentrate-System-Cleaner/dp/B00092893E/

If doing that doesn't work for you, then just get the valves cleaned for ~$500 if you start noticing a loss of performance. If you don't notice any performance loss then there's nothing wrong with your valves.

It's not as big of a deal as some people make this out to be.

Ray Pickle Enthusiast

Ray Pickle

Posted
Posted

D.I. fuel delivery is employed in over 55% of powertrains presently produced. The real issue of intake valve carbonization is a simple matter of understanding the need to change old ways/habits as it relates to maintenance. Use appropriate chemicals at appropriate intervals and the likelihood of having to deal with worst case scenario of manual valve cleaning is minimized. Pretty much like everything else related to vehicle maintenance. 

Jettech1 Senior Enthusiast

Jettech1

Posted
Posted
On 3/27/2023 at 10:57 PM, Dr1ft3r said:

Use top tier fuels and run cleaner through it every now and then.

I am using this every 6,000 miles:
https://www.amazon.com/Chevron-Techron-Concentrate-System-Cleaner/dp/B00092893E/

If doing that doesn't work for you, then just get the valves cleaned for ~$500 if you start noticing a loss of performance. If you don't notice any performance loss then there's nothing wrong with your valves.

It's not as big of a deal as some people make this out to be.

Everything you put in your tank of fuel will only go through the injectors.  It has nothing to do with the backside of your valves.  That's where intake cleaners come into play.  The best ones to use, I have no idea.  But seafoam has always been good to me.  Is it the best...who friggen knows...but it did help on my 2014 impala big time.  I put my eyes on them before and after.  So it worked amazing.  I've read great reviews from Amsoil intake cleaning products and BG products as well.  Any cleaner you want to introduce to the backside of the valves has to go through the intake, not the gas tank.

Grumpy Bear Senior Enthusiast

Grumpy Bear

Posted
Posted

Blow-by gas is an interesting subject. Observations for what they are worth. All ventilation systems move gas by pressure differential. Manifold vacuum is the driver and until rings expire will be the major driver. Vacuum drawing fresh highly filtered air via the intake system on modern vehicles.  The inside of a motor looks like a hurricane hit it. Oil expelled from rod journals whipped by the rotating assembly a major source of 'misted' oil. The baffles in the valve cover or some other device doing the bull work of separating that mist from the air draw. Some gas, blow-by gas, does get past the rings enter the sump. Mostly water vapor and hot combustion byproducts. If you motor seals well this is the smaller part. Mist the larger. 

 

That isn't carbon on the backside of intake valves. Never gets hot enough even during the hot soak to reduce the hydrocarbons to carbon. It's the polymers, mostly VVI polymers glued together with the light ends of oil and Un combusted gasoline. That is the short and dirty version. 

 

So, limit blow-by by getting a good ring seal and use an oil with low volatility and as little VVI as possible. 

 

This is Cameron's motor mentioned above at 104K miles. GDI isn't an automatic death sentence. 

 

image.jpeg.4ea508afade06f9c22d0819f910990bb.jpeg

  • Like 2
Dr1ft3r Enthusiast

Dr1ft3r

Posted
Posted (edited)
6 hours ago, Jettech1 said:

Everything you put in your tank of fuel will only go through the injectors.  It has nothing to do with the backside of your valves.  That's where intake cleaners come into play.  The best ones to use, I have no idea.  But seafoam has always been good to me.  Is it the best...who friggen knows...but it did help on my 2014 impala big time.  I put my eyes on them before and after.  So it worked amazing.  I've read great reviews from Amsoil intake cleaning products and BG products as well.  Any cleaner you want to introduce to the backside of the valves has to go through the intake, not the gas tank.


If adding anything to the fuel has zero effect on carbon deposits, or any other type of deposit, then why would using top tier fuels as instructed by GM matter either? The only difference between top tier fuel and fuel not rated as top tier are the detergents used in the fuel.

Think on that.

Also, it is my understanding that changing the oil sooner has a positive effect on deposits accumulating in your engine.

 

Top Tier Fuel.png

Top Tier Fuel 2.png

Edited by Dr1ft3r

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share
Go to topic listing

  • Latest Articles

  • Posts

    • asilverblazer
      Wow I'm in a pickle. (Broke down truck) and a story.

      By asilverblazer · Posted

      There's a bunch of tea leaves that you've read, but in any case the delayed timing is unusual. Not sure how that relates to the rich at idle vs. 'normal' while driving.   If you're in this deep, might be worth investigating, and re-learning the sensor. What have you got to lose? Plus, it properly fixes the timing cover leak.
    • asilverblazer
      Wow I'm in a pickle. (Broke down truck) and a story.

      By asilverblazer · Posted

      The only problem I have seen this cause is longer crank times. 
    • Atlas
      Wow I'm in a pickle. (Broke down truck) and a story.

      By Atlas · Posted

      Injector is being sent off today for rebuild and I estimate I'll have it back in 10 days or so.   It may not be the injector...of course...now that I've torn down the intake again. But, let's rule out the injector and replace those spider legs that have been almost rubbed through.   The truck has always had negative timing and I'm reading "normal" timing at warm idle should be +16 or so. I'm negative 16 to 25 or more, and it's always been like that since I bought it.   A light turned on upstairs last night in the old noggin. Rare, I know...   This will be wild, if it turns out to be the cause!   In 2001, according to the old service documentation, the muffler was replaced. Why? I have no idea, it wouldn't have been rusted through by then. But they did a crappy job.   In 2019, another shop replaced it and noted the prior install was poorly done on the work order. "Exhaust system vibrates on crossmember". Except...I guess they just left it be? I believe the husband, the couple who were original owners, had passed by then. Maybe she said it's just not worth it to have the exhaust system fixed and declined repairs. Very few miles were driven between 2019 and 2025.   The exhaust system vibrates heavily on the crossmember and you can feel it and REALLY hear it, even today. Not always, but at idle, it gets going pretty good sometimes.   What if....   ....What if that's enough to trigger one or both of the knock sensors? Could it be tricking the sensors into sensing knock, so it's pulling timing aggressively? Pulling timing heavily means it's firing after the piston reaches full height which means incomplete burn which means the O2 sensor is sensing a rich condition, which means I've been chasing my tail, and what I thought was an inconsequential problem (janky exhaust) has been THE issue for this truck for 25 solid years?   That would be wild. Maybe it IS wild.   The service documentation thereafter, for years, shows visits for rough idle, replacing O2's, replacing the cat, replacing plugs and wires, a misfire condition, like they could never solve the issue. The injector has been replaced 4 times in 80k miles, that's just crazy.   The secondary theory....   The engine has clearly had a leak at the front seal for a very long time (the greasy trench...). I think the truck changed hands quickly ~2025 because there's Napa receipts from someone I don't recognize in the ownership history. They apparently replaced the timing cover seal, and they did a terrible job. There's RTV smeared all over and the leak I had reduced to a weep by snugging the front oil pan bolts is now a leak again.   HOWEVER....I read about replacing the crankshaft position sensor. Any time the ckp sensor is disturbed or timing cover is removed, the truck requires relearning, and that can only be done through a bi-directional scan tool. Skippy with the RTV probably didn't do the relearn procedure is my guess. His scan tool is lost in a pile of RTV goo somewhere.   So, it's very possible the sensor has been disturbed and the truck is just running on the old learn data but not setting a code for anything. The distributor has since been replaced and so has the camshaft position sensor, so all bets are off for that thing.   In the theme of one step forward, two steps back, I returned the accumulator for the AC. The gal I've been working with at O'Really's has been great. She refunded it under manufacturer's defect and we compared it to the replacement I ordered, and sure enough, the replacement is machined very differently (and a gauge actually fits on it!).   Got it home, installed it, started vacuuming it down.... and I couldn't get good vacuum.   The high side service port, where I replaced the old GM ball valve suspecting that was a source of the previous leak....well, I've clearly exposed whatever pre-existing crack in the line where the service port is welded, and made it much worse. Blessing in disguise? Except there goes another $25, now I'm waiting for a replacement AC line.   In 10-ish days ALL the parts will be here. Rebuilt injector, new exhaust system, new cat, new high pressure AC line.   Oh, did I mention the squeaking ISN'T coming from the AC pump? The truck still squeaks when started, and there were words after I started it with the new AC pump installed. But, there was more to replacing the AC pump for just a squeak. A truck with good working AC is something of value, for the comfort alone.   I've ordered a new harmonic balancer because, 30 years is a good run for one of those. Rule it out. The squeak may be something more sinister, though. I'm worried about that ckp sensor and if it was shimmed correctly, or if the timing set was installed correctly. The squeak may be coming from UNDER the timing cover.   At this point, once I get it put back together, I'm thinking I'll take a 50 mile victory lap and then promptly put it up for sale. This truck is cursed. Betty, from beyond the grave, doesn't want anyone messing with her Blazer. Or maybe she's getting revenge for 30 years of shop visits with that thing.
    • KARNUT
      Gas Prices

      By KARNUT · Posted

      3.59 Kroger’s in Montgomery Tx. 20 cents higher than most around here. Very unusual. Saturday they were 3.49. 
    • KARNUT
      Travel Trailer 2024 2500 HD 6.6 Gas Engine ?

      By KARNUT · Posted

      Starting at 17 running parts for my father’s construction business to haul our equipment. Eventually doing shows, sales and training after purchase. I drove a minimum of 50K miles a year. Half hauling something. After retiring 30K miles a year to the last 2 years 15K miles a year. 2/3rds highway driving. The major contribution to fatigue for me is from anticipation and awareness. I just don’t relax. Too many idiots on the road. There’s two kinds. The group that never leave the left lane tied together afraid to let anyone in doing 80. They’re mostly on weekends. Then the left lane sleepers usually next to a tractor trailer not advancing. Eventually the tractor trailer will drift over the sleeper will wake up. The train moves and the tailgaters who are usually mad as hell. You definitely don’t want to mix with them. The tail wagging bumper puller’s with under powered trucks are holding the tractor trailer up. That bunch are dangerous. I usually pace ahead all that. Unless there’s a gap when I can chill and let the speeders pass. I tried all different types of driving. I stay to the right except to pass, it’s the law that’s getting in forced more now because of road rage. I was so happy when my wife didn’t want to do the camping life. I had enough of pulling for work. The family has a bus and fifth wheel. I haven’t driven either one since retiring. No thanks. 

  • GM-Trucks.com Clubs

  • Popular Contributors

×
×
  • Create New...