6.6 Gasser Longevity

[UltimateToolReviews]

Ford seems pretty hit or miss with the HD gas engines, My last Ram 2500 had zero issues BUT the 6.4 hemi can develop the hemi tick and mine was starting to tick worse and worse at 70k miles, seems like the 6.6 was the most problem free HD gasser out there. My mechanic has told me he only sees them for oil changes and brakes, the other brands he sees for more repairs often. I think the 6.6 is great choice for now. However the new 10 speed is up in the air IMHO, I went with a 2022 with the 6 speed.

[mrjulian416]

17 hours ago, C/K Man said:

A lot of people think that intake valve deposits are the only result of crankcase blow-by.  That isn't true, a lot of the deposits are caused by the EGR affect of variable valve timing.  Instead of using EGR valves like older engines did, modern VVT engines accomplish the same thing by advancing cam timing to the point that the intake valve starts to open before the piston reaches TDC on the exhaust stroke.  This blows exhaust up through the intake port past the open intake valve, and the exhaust is almost immediatly drawn back into the cyinder on the intake stroke when the exhaust valve closes and the piston goes back down.  The hot exhaust will condense on the cooler back side of the intake valve and port and that's what causes the deposits.  Using a higher quality 'Top Tier' gasoline will reduce both intake valve and combustion chamber deposits.  It's less of an issue in California due to the cleaner (and more expensive) gasoline formulation.         

This is the truth that many people just don't want to accept (especially people who sell catch cans).  I've linked it before, and here it is again, but actual engineering research has shown blow-by has almost no effect on valve deposits in DI engines.  In fact, in the testing, when they completely bypassed the PCV lines, there was slightly more deposit formation.  The biggest factor is engine load, with low load levels generating more deposits than high load... which comes down to the EGR phenomenon C/K Man references above.

 

Considerations on Influencing Factors of Carbon Deposit in Gasoline Direct Injection Engine

 

Yes, Top Tier fuel can help, especially with carbon inside the combustion chamber, and to some extend on the intake valves as well.

[C/K Man]

E85 helps a lot too!  I wish GM would make E85 capability at option on the L8T again.

[lundimpact1775]

Bring it to a reputable tuner and have them do the e85 conversion. 

 

Despite the other issues I e had related to GM quality, the L8T is very fun to drive on corn gas and with a proper ECM and TCM tune. 

 

Twin cities performance (CJTunes) did mine. It keeps me happy with an otherwise problematic vehicle. Smiles per gallon are unmeasurable

[MORSNO]

15 hours ago, lundimpact1775 said:

Bring it to a reputable tuner and have them do the e85 conversion. 

 

Despite the other issues I e had related to GM quality, the L8T is very fun to drive on corn gas and with a proper ECM and TCM tune. 

 

Twin cities performance (CJTunes) did mine. It keeps me happy with an otherwise problematic vehicle. Smiles per gallon are unmeasurable

 

I've never lived anywhere that had e85 gasoline, what does it do to your mileage and towing/hauling power?  I've heard it is abysmal. 

[No F-bdy Bs]

16 hours ago, lundimpact1775 said:

Bring it to a reputable tuner and have them do the e85 conversion. 

 

Despite the other issues I e had related to GM quality, the L8T is very fun to drive on corn gas and with a proper ECM and TCM tune. 

 

Twin cities performance (CJTunes) did mine. It keeps me happy with an otherwise problematic vehicle. Smiles per gallon are unmeasurable

What year is your truck, and what other issues have you had? 

[Grumpy Bear]

45 minutes ago, MORSNO said:

 

I've never lived anywhere that had e85 gasoline, what does it do to your mileage and towing/hauling power?  I've heard it is abysmal. 

 

I've been running E-85 for several years. I've learned it's cost it is a point of reference issue. 

 

1.) First off, E-85 at 77%, our local usual delivers about 30% less miles per gallon. Which means the E-85 has to be 30% cheaper to buy to cost the same per mile. If you are comparing the cost of E-85 to E-10 regular 87 octane that is a margin you will not often win. If however you are comparing to a top tier premium fuel then you win hands down every day in every way. Locally I buy BP E-85 today at $2.599 / gallon. Shell V Power Nitro + 93 sells for $4.009 per gallon. I save 20 cents per gallon after the milage offset. 

 

2.) It does make more power, just. 4% according the GM. Does make about 25 lbs./ft. more torque. Will you notice? 

 

3.) E-85 burns very clean and cool. So clean you will absolutely notice it in the color of your oil vs miles/time. 

 

4.) This one I've measured. My motor takes (OEM book suggested) 87 octane fuel and the Knock Sensor is pulling timing often and hard. On even 95 octane Premium it still pulls timing. Just not as hard. On alcohol at anything over 50% I can't force it to remove timing. 

 

5.) Bore wear is equivalent to most top tier fuels. 

 

Those are the pluses. The negatives are:

 

1.) It can be finicky to start is sub zero weather UNLESS you reduce the alcohol content to about 50%. It will start, just spins the starter longer. Cost wise that is a wash. Very predictable sliding scale of fuel blend cost vs milage. I've worked the horse and it pays the same.

 

2.) Can be hard to find in some markets nation wide. Keep the flex fuel option if you can. Shop price and use a trusted supplier. True of any fuel.

 

3.) More fuel stops. At my age that is moved to the plus column.  

 

Final notes.

 

1.) A dedicated E85 tune will get even better mileage than the OEM Flex-Fuel mapping. 

 

2.) Bore wear can be less on Shell V Power Nitro + and Mobil/Exxon Synergy Supreme + due to some friction/anti-wear modifiers used in those two fuels. Shell comes out a wash on fuel cost. Mobil requires selling children to run. KR timing pull will be in play again. Oil gets dirtier earlier. So some trades to consider. 

Edited May 29, 2025 by Grumpy Bear

[lineman1234]

I was going to get the E85 option when ordering mine last year. ( if i could ) I ended up getting one very close to what i would have specked mine out ordering on the lot. 

     It didnt have the E85 option on it. 

 

I have looked and researched, even asked a couple dealers about possibly getting it added, if i could. 

They said they have no idea on how or if it can be factory added. 

 

Hear in the very, very upper part of Minnesota, E85 is easy to get, and always $1 or more less than 87 with 10-15% ethanol in it.

When fuel prices bounce up and stay there, the E85 seems to stay at its lower price. 

 

Does anyone really know the facts of what is the difference in a stock 6.6 gasser and one with the E85 option added from the factory. What does it add other than computer programing??

     I would only stick with factory.

 

 

[lundimpact1775]

4 hours ago, lineman1234 said:

I was going to get the E85 option when ordering mine last year. ( if i could ) I ended up getting one very close to what i would have specked mine out ordering on the lot. 

     It didnt have the E85 option on it. 

 

I have looked and researched, even asked a couple dealers about possibly getting it added, if i could. 

They said they have no idea on how or if it can be factory added. 

 

Hear in the very, very upper part of Minnesota, E85 is easy to get, and always $1 or more less than 87 with 10-15% ethanol in it.

When fuel prices bounce up and stay there, the E85 seems to stay at its lower price. 

 

Does anyone really know the facts of what is the difference in a stock 6.6 gasser and one with the E85 option added from the factory. What does it add other than computer programing??

     I would only stick with factory.

 

 

 

1) GM flex fuel sensor (would be factory on a flex capable truck) 

2) wideband map sensor, I believe. My tuner added this as part of their package. He's well known, twin cities performance is the name of the shop. Located in Saint Paul

3) ECM had to be bench unlocked at HP tuners. Apparently it's the only way to get into global B platform.

4) the actual tuning. I opted for a street tuned rather than Dyno, since it's not a race car and I didn't want to buy an aftermarket drive shaft. 

 

Stock L8T with 6l90 and 89k miles ran 0-60 in about 9.5 seconds. I'm getting 6.5 seconds running on e85 now. We set up the tables to run e85 or 91, since 91 is prevalent around here. I've considered re-tuning for e85 and 87, but I do like the benefit of no or very little KR. I run 91 in the winter to avoid excessive cranking times. 

 

Mpg's about 30% Lower on corn, as one would mathematically expect. Interestingly, mpg's while towing on e85 are actually not as far off as the 91. 

 

To answer the other question above, I had some real bad luck with my hpfp and the OEM replacement that went in after the first one failed. Trans cooler seems to get plugged up with leaves and debris more than any other vehicle I've ever owned. It's noisy which I've observed with other using l8t's but not all of them. The noises seem to vary quite a bit from one unit to the next. Also some battery issues, and interior quality is very sub par. 

 

It's still a fun truck after the tune. It pulls whatever I care to connect to it, and interior space is outstanding for my growing family. 

[MORSNO]

On 5/29/2025 at 8:30 AM, Grumpy Bear said:

 

I've been running E-85 for several years. I've learned it's cost it is a point of reference issue. 

 

1.) First off, E-85 at 77%, our local usual delivers about 30% less miles per gallon. Which means the E-85 has to be 30% cheaper to buy to cost the same per mile. If you are comparing the cost of E-85 to E-10 regular 87 octane that is a margin you will not often win. If however you are comparing to a top tier premium fuel then you win hands down every day in every way. Locally I buy BP E-85 today at $2.599 / gallon. Shell V Power Nitro + 93 sells for $4.009 per gallon. I save 20 cents per gallon after the milage offset. 

 

2.) It does make more power, just. 4% according the GM. Does make about 25 lbs./ft. more torque. Will you notice? 

 

3.) E-85 burns very clean and cool. So clean you will absolutely notice it in the color of your oil vs miles/time. 

 

4.) This one I've measured. My motor takes (OEM book suggested) 87 octane fuel and the Knock Sensor is pulling timing often and hard. On even 95 octane Premium it still pulls timing. Just not as hard. On alcohol at anything over 50% I can't force it to remove timing. 

 

5.) Bore wear is equivalent to most top tier fuels. 

 

Those are the pluses. The negatives are:

 

1.) It can be finicky to start is sub zero weather UNLESS you reduce the alcohol content to about 50%. It will start, just spins the starter longer. Cost wise that is a wash. Very predictable sliding scale of fuel blend cost vs milage. I've worked the horse and it pays the same.

 

2.) Can be hard to find in some markets nation wide. Keep the flex fuel option if you can. Shop price and use a trusted supplier. True of any fuel.

 

3.) More fuel stops. At my age that is moved to the plus column.  

 

Final notes.

 

1.) A dedicated E85 tune will get even better mileage than the OEM Flex-Fuel mapping. 

 

2.) Bore wear can be less on Shell V Power Nitro + and Mobil/Exxon Synergy Supreme + due to some friction/anti-wear modifiers used in those two fuels. Shell comes out a wash on fuel cost. Mobil requires selling children to run. KR timing pull will be in play again. Oil gets dirtier earlier. So some trades to consider. 

 

Thank you, Grumpy Bear, excellent review and education!  You're the first person to actually give a reasonable explanation.  

[C/K Man]

Sorry for not being the best picture, but this is a bore scope view of the #1 cylinder in my 145,000 mile 5.3L 2011 Yukon.  This vehicle has been running on E85 about 80% of the time, never been apart.  

[Grumpy Bear]

3 hours ago, C/K Man said:

Sorry for not being the best picture, but this is a bore scope view of the #1 cylinder in my 145,000 mile 5.3L 2011 Yukon.  This vehicle has been running on E85 about 80% of the time, never been apart.  

 

Outstanding!! Thanks for the snap.

[lineman1234]

Its quiet hear........

 

Im almost at 50,000 miles.  2024 WT 3500 6.6 gas.  Mostly used as a car. About 7,000 miles towing a 10,000lbs 5ver and now 3,000 so far doing the truck camper thing. 

            No notable oil usage. The factory battery crapped out after a few months and a wire for one of the 2 before cat sensors burnt to the exhaust and blew the fuse, causing all kinds of problems. Both things happened at the same time. I cant remember the mileage but stull under warranty. 

 

I am on a winter truck camper south wandering tour loaded about 500lbs under my max payload, and the thing handles and drives very nicely .The rear overload springs arent even touching. 

 

 Im very happy with it. 

[MORSNO]

22 hours ago, lineman1234 said:

Its quiet hear........

 

Im almost at 50,000 miles.  2024 WT 3500 6.6 gas.  Mostly used as a car. About 7,000 miles towing a 10,000lbs 5ver and now 3,000 so far doing the truck camper thing. 

            No notable oil usage. The factory battery crapped out after a few months and a wire for one of the 2 before cat sensors burnt to the exhaust and blew the fuse, causing all kinds of problems. Both things happened at the same time. I cant remember the mileage but stull under warranty. 

 

I am on a winter truck camper south wandering tour loaded about 500lbs under my max payload, and the thing handles and drives very nicely .The rear overload springs arent even touching. 

 

 Im very happy with it. 

 

Good to hear, thank you for the updated information. 

[Shatterz]

68k miles here and no problem issues. Have a 3500 L8T at work as well with 128k that’s gone through 2 6L90s but the engine is solid. 
 

My guess on what’s the first thing to go on these that is irrespective of maintenance or usage, the high pressure fuel pump for direct injection. About 2100 PSI cam driven and it’s only a matter of time until they go very similar to a diesel’s high pressure pump in design. Located on the very back of the engine nearest the firewall and under the intake manifold it will be a joy to one day replace .