LMM Headgasket

[Duramaster]

I just replaced a set of head gaskets on an '08 LMM the other day. UGG! I don't want to have to relive that one anytime soon! I did the repair because of coolant consumption AND an over pressurized cooling system. Anyone else out there with an LMM having any slow coolant loss issues? :confused:

[Mark Rinker]

How did you do the gasket swap? Pull fenders/cab off engine, or pull engine out of truck?

[Duramaster]

GM Service Information says to remove the engine from the truck for the repair. I had no interest in that!! On the flip side, I don't have the ability to pull the cab up off of the frame, so I did the job in the vehicle. I didn't even pull the turbocharger. It still took way too long to do the job, but I had no left-over parts and I wasn't shy any either. :D

[Mark Rinker]

You must have skinny, nimble hands. :)

[More Power]

Did you pull both heads? Were you able to identify the leak site on the gasket(s)?

What do you think caused the leak?

How did you prep the heads/block for re-assembly?

Thanks.

Jim

[Dakster]

Thankfully that is one problem I do not have... Sounds like you had a lot of fun Duramaster!

[Duramaster]

The only leak that I could positively indentify was the EGR Cooler leak. I added coolant dye to the cooling system and then had the Service Manager go on a 40 mile road test. I pulled the glow plugs and found no evidence of dye. I pulled the intake manifold (upper) and the EGR valve and found a little puddle of dye present inthe EGR cooler. The reason I replaced the head gaskets was because when the truck came to me, I noticed that the cooling system was under extreme pressure. The radiator hose was "ROCK HARD" and that was when cold. Now I suppose you could argue that the exhaust pressure in the EGR cooler could be pressurizing the cooling system, but then I would think that the pressure would subside after the engine has shut down. This was the vehicles second trip into the dealer. The first time the other technician had found nothing except a leaky coolant resevoir. As far as my skinny nimble hands go, well they're far from skinny. :p I just like to tear into the tougher jobs. And besides that, there is only two of us here that work on the DMAX V-8 and the other guy doesn't like working on the pickups because he doesn't like bending over the fenders (he's a little bit on the short side :p )

[More Power]

Thanks for the comeback! Was the EGR cooler replaced or did you discover why/how coolant got into the sooty side of the EGR cooler?

Thanks again for keeping us informed...

JIm

[Duramaster]

I did replace the EGR cooler. There are a couple of bulletins relating to the egr cooler leak. One states to check for restricted coolant hoses and the other refers to coolant in the cylinders.



Subject: Diesel Engine Coolant Loss Leak From EGR Cooler


Models: 2007-2008 Chevrolet Express, Kodiak, Silverado

2007-2008 GMC Savana, Sierra, Topkick

Equipped with the 6.6 diesel engine RPO code LMM




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This PI was superseded to update model years and reference to bulletin 08-06-04-003. Please discard PIP4135A.


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The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

Condition/Concern:
The customer concern may be coolant loss. During diagnosis the coolant may be found in the combustion chamber.

Recommendation/Instructions:
Complete the current SI diagnostic for any trouble code or symptom found. If coolant loss has been verified, and a cooling system pressure test was to show coolant leaking into a combustion chamber, inspect for a leaking EGR cooler. Please use the newest version of bulletin 08-06-04-003 for a description of EGR cooler pressure testing.

If coolant has been found in a combustion chamber, remove the glow plugs and rotate the engine over by hand to purge any remaining coolant out of the cylinders.

Replace the EGR cooler as needed. When the EGR cooler is replaced it's very important to be sure all air is purged from the cooling system. Please use the SI procedure for Cooling System Draining and Filling (Vac-N-Fill) if possible.

Note: Running the engine without coolant flowing to the EGR cooler may result in cooler damage. Do not run the engine with the coolant hoses disconnected.

Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.




Subject: Coolant Loss From EGR Cooler or DTC P2457


Models: 2007-2008 Chevrolet Express, Kodiak, Silverado

2007-2008 GMC Savana, Sierra, Topkick

Equipped with the 6.6 Diesel Engine RPO code LMM




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The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

Condition/Concern:
A dealer may encounter a customer concern of coolant loss, coolant odor, or DTC P2457.

Normal diagnosis will lead to a leaking EGR cooler. The EGR cooler may have been replaced more than once.

Recommendation/Instructions:
If a dealer has encountered a leaking EGR cooler (may be repeat repair), DTC P2457, or a strong coolant odor, inspect for cooling system/heater system modifications. Modifications for a rear heater or a fuel operated heater (FOH) may cause poor flow (or no flow) through the EGR cooler. If coolant flow through the EGR cooler is restricted, the cooler can overheat. Overheating may induce an internal coolant leak from the EGR cooler. Verify the modifications made to the vehicle cooling/heater system have not restricted flow through the EGR cooler.

Improper routing of coolant supply hoses may also induce EGR overheating. If the vehicle has been modified for rear heat or FOH, inspect for proper hose/line routing. It is important to note the difference between supply and return especially if an auxiliary coolant flow pump is utilized to aid in coolant circulation to the rear auxiliary heater core. Some vehicles (RPO code ENC) are equipped with coolant supply and return lines under the passenger side of the cab. These lines can also be swapped/misrouted due to the differences between the diesel or gasoline line positions. Verify the supply and return lines are in the proper positions.

For diesel engine equipped vehicles the outboard pipe (as viewed from the rear of the vehicle) is the supply of engine coolant to the rear auxiliary heater. The inboard pipe is the return of engine coolant from the rear auxiliary heater to the engine cooling system.
For gasoline engine equipped vehicles, the inboard pipe (as viewed from the rear of the vehicle) is the supply of engine coolant to the rear auxiliary heater. The outboard pipe is the return of engine coolant from the rear auxiliary heater to the engine cooling system.
Note: To aide in proper filling of the cooling system, please use the SI procedure for Cooling System Draining and Filling (Vac N Fill).

Note: Dealers should contact the GM upfitter (www.gmupfitter.com) for instructions on adding rear heaters and/or fuel operated heaters.

[madmatt]

I had a LMM that was running hot due to a leaky EGR valve but have not had the "pleasure" of pulling the heads on one yet.