6.6 Gasser Longevity

[MORSNO]

How many miles do you have on your 6.6 and how is it holding up?  I have a 2012 6.0 gasser which seems to be bulletproof and wondering if the 6.6 is proving itself as a worthy upgrade with a new truck in the future?  Thanks everyone!

[the8rotor]

Great engine. I put 32k on my 2021 GMC 2500 gasser, have 26k on my 2024 Cheby 2500 gasser. Neither have used any oil, tow great, and been super reliable. Highly recommend!

[AndrewF]

We should have a thread for highest mileage L8T. Saw one on marketplace for sale that was a fleet vehicle with 450k on it. No idea if it was original engine though. 

[No F-bdy Bs]

I don't doubt it's a 300k+ engine. It has no real weaknesses, and it's been out long enough so that there's plenty with enough miles where we'd know if it had an inherent design flaw. It's on it's 6th year, and aside from a few spotted cases of oil consumption, it's not having any other issues. 

 

The only drawback to longevity is the direct inj, which won't exactly "damage" the engine per se, but probably will require addressing every 125k or so. 

 

I personally think it's the best powerplant for reliability offered in any light duty truck. 

[lineman1234]

54 minutes ago, No F-bdy Bs said:

I don't doubt it's a 300k+ engine. It has no real weaknesses, and it's been out long enough so that there's plenty with enough miles where we'd know if it had an inherent design flaw. It's on it's 6th year, and aside from a few spotted cases of oil consumption, it's not having any other issues. 

 

The only drawback to longevity is the direct inj, which won't exactly "damage" the engine per se, but probably will require addressing every 125k or so. 

 

I personally think it's the best powerplant for reliability offered in any light duty truck. 

Im just curious to why the 6.6 direct injection might need addressing every 125,000 miles and what it might need? Otherr than normal maintenance and such pointed out in the  manual. 

[PunchT37]

Good little compact pushrod engine without DFM or stop/start. Has iron block for high hp builds. Favorite for hotrod swaps.

[MORSNO]

24 minutes ago, PunchT37 said:

Good little compact pushrod engine without DFM or stop/start. Has iron block for high hp builds. Favorite for hotrod swaps.

 

That's why I'd hope it's a good engine for longevity.  The oil consumption issue a few are having is the only thing that has popped up on my radar to watch.  The engines with oil consumption seem to have it from new, so it's not necessarily a maintenance issue but something in the build. 

[mrjulian416]

The 125k mileage comment is likely referring to the need in some direct injection engines to have their intake valves to be de-carboned every 100-150k miles.   This is typically done in a shop using walnut blasting after removing the intake manifold.   

 

 

[OS RR]

21 minutes ago, mrjulian416 said:

The 125k mileage comment is likely referring to the need in some direct injection engines to have their intake valves to be de-carboned every 100-150k miles.   This is typically done in a shop using walnut blasting after removing the intake manifold.   

 

 

 

 

Is this something running "Top Tier" fuel can help? Gonna be honest, I run the cheapest 87 I can get (usually from Krogers using points). I've also ran a tank of "88" from Sheetz (basically E15).

[BuckWallace]

3 hours ago, OS RR said:

 

 

Is this something running "Top Tier" fuel can help? Gonna be honest, I run the cheapest 87 I can get (usually from Krogers using points). I've also ran a tank of "88" from Sheetz (basically E15).

No, the "issue" is that since the fuel is injected in the combustion chamber rather than the intake port it's not washing the back of the intake valve, which leads to the carbon buildup. It won't matter what type of fuel you use.

[Pryme]

I have a whopping, mind boggling 14,800 miles on my 22. It’s holding down my garage nicely with its 7,300 pounds of chunky. No oil burning from my garage cream puff. 
 

now if you’ll excuse me, it’s due for its carnuba massage. 

[Another JR]

55 minutes ago, Pryme said:

I have a whopping, mind boggling 14,800 miles on my 22. It’s holding down my garage nicely with its 7,300 pounds of chunky. No oil burning from my garage cream puff. 
 

now if you’ll excuse me, it’s due for its carnuba massage. 

I use my 2021 to reduce the amount of air swirling around in my barn. 

 

[No F-bdy Bs]

20 hours ago, OS RR said:

 

 

Is this something running "Top Tier" fuel can help? Gonna be honest, I run the cheapest 87 I can get (usually from Krogers using points). I've also ran a tank of "88" from Sheetz (basically E15).

It won't make any difference since the fuel, regardless of tier, never contacts the valves. 

Just a necessary evil of Di. 

[jake111]

Is the claim for Top TIer (which both my truck and hybrid RAV4 highly recommend) that the little bit that blows back into the intake (for EGR) helps keep it clean?  That would mean the extra detergents survive combustion.  Hmmm.  I wonder if there are any real-world studies?  Or at least anecdotes? 

 

Costco is cheapest when I'm at home.  On the road it would be convenient and cheaper to use Maverick or others.

 

[ADDED] Read a few more articles/opinions.  Meh.  Maybe I'll just use Top Tier given a choice but not hesitate to use cheaper selections when traveling.

Edited May 17, 2025 by jake111

[C/K Man]

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.