Overheating towing with Denali 6.2L - Losing my F'n mind!!

[Ming15237]

Hello everyone. I am new to the forum but have been lurking for a while. I would appreciate any help you call could provide on my issue. There are several other posts on this subject but I thought I would start a new thread as a last ditch effort to keep me from losing my friggin' mind and selling or trading in my beloved Yukon Denali.

The truck is a 2008 Yukon Denali 6.2L AWD with 119K miles. Overall the truck has been very well taken care of and hasn't done much towing in it's life. I've had it for the last year and a half and it had about 95K miles on it when I purchased it from an older gentleman who had taken really good care of it and did not tow with it.

I purchased the Denali because I like all the interior room and features but also I have a 20ft flat bed trailer that I use to tow my two Polaris RZRs and occasionally 3 RZRs out to the trails in the Colorado mountains and surrounding states. With the the trailer and 2 RZRs, the total towing shouldn't be more than ~5K lbs, which is well within the tow rating. Up until 6 weeks ago, it had performed flawlessly towing. I have used it to tow the two and even three RZRs and 6 people in the truck up and down most of the major passes in Colorado. About 8 weeks ago, me and a friend were taking my two RZRs up to some trails out past Divide CO. We drove up a relatively short incline that has a stop light at the top. When I got to the top of the hill and stopped for the light, the truck died. The dash lit up, the temp was way above normal and the DIC displayed a message about the overheat condition. Long story short, after getting towed to a shop and sitting for an hour, it started back up, ran fine and got us and the trailer back home on the downhill and flatter roads back to the house. I carry a scan tool in the truck and no codes were recorded and the check engine light was not on after it finally started back up. The shop confirmed no codes and performed a pressure test on the cooling system, which it passed.

Over the last few weeks I have replaced the following items:
Water pump
Thermostat
Fan Relays
Fan switch
Coolant temp sensor
Radiator
Radiator fans
Radiator fluid (original fluid was very clean when I replaced it)

Tonight I took the truck for a test drive with just the trailer attached. With some aggressive driving on an almost flat road by my house, the truck did the exact same thing. The temp shot up to 240-250 (I was using Torque and a bluetooth OBDII scanner to get an accurate temp reading), trans temp was around 210 (seems normalish) and when I pulled up to a light it shut off and wouldn't restart for almost exactly an hour again. Again no codes were recorded, no check engine light triggered.

The truck doesn't seem to be losing any coolant. While driving around Denver with no trailer, the temp stays around 200-210 in 95 degree heat and runs just fine. One thing I did notice that I thought was odd, when I replaced the radiator, almost no ATF came out of the trans cooler. Is that a problem? I am really frustrated at this point with the truck. I really love this thing but if it can't tow my ****, it's no good to me! If anyone has any ideas, I'd love to hear them.

I’m an ASE certified master tech, provided that the cooling fans are working, I am fairly certain that you have a failed head gasket or a cracked cylinder head. Simple removal of the spark plugs by a qualified tech and review of the plugs will normally yield a diagnosis. The first and most simple test I do for a suspected bad head gasket is remove the engine drive belt on a cold engine, remove radiator cap. Start engine, if you see ANY bubbles you have a failed gasket or a cracked head.

 

[Ming15237]

I’m an ASE certified master tech, provided that the cooling fans are working, I am fairly certain that you have a failed head gasket or a cracked cylinder head. Simple removal of the spark plugsby a qualified tech and review of the plugs will normally yield a diagnosis. The first and most simple test I do for a suspected bad head gasket is remove the engine drive belt on a cold engine, remove radiator cap. Start engine, if you see ANY bubbles you have a failed gasket or a cracked head.

 

[ncampion]

Check oil pressure at idle hot. If below 20 it will go into limp mode, if below 17, it will shut down. May look like an overheat problem but really a low oil pressure problem. 6.2 motors had problems with cam bearing wear causing low OP. I had this problem with my 08 6.2. Had to replace engine do to GM screw up with cam bearings.

 

[gpracer1]

I’m an ASE certified master tech, provided that the cooling fans are working, I am fairly certain that you have a failed head gasket or a cracked cylinder head. Simple removal of the spark plugsby a qualified tech and review of the plugs will normally yield a diagnosis. The first and most simple test I do for a suspected bad head gasket is remove the engine drive belt on a cold engine, remove radiator cap. Start engine, if you see ANY bubbles you have a failed gasket or a cracked head.

I would think that a cracked block or blown head gasket would show one of several symptoms........water in oil, a cylinder misfire, low coolant level from combustion gases over pressurizing the cooling system, white smoke out the tail pipe, etc. But for overheating it will be due to low coolant level from the escaping/leaking coolant if block or head gasket is suspected.
Also ASE master tech since 1991.

 

[EfrainlCazares]

What I find interesting is that no one seems to notice the truck over heating and no messages on the DIC to that effect until after the truck stalls out... which leads me back to my overheated fuel/vapor lock assumption.

I think if I were doing a lot of towing or if I had the 6.0/6.2L my first 2 upgrades would be to wrap the fuel lines and upgrade to the Mishimoto radiator or something equivalent.

I didn't have the shut off, but the engine and transmission temps jumped to 225 and 230. I bought a three core radiator. I kept the same temp thermostat and added an additional transmission cooler. Now my normal temot in town are 150 and on the road , about 165

 

[JEFFC]

An easy way to see if the no start when towing is related to vapor lock is to bleed gas off at the fuel rail while cycling the key several times to on several times without starting. (as someone earlier mentioned) The safe way to do it is with a fuel pressure tester so you can bleed the fuel outside of the engine compartment. This test must be done during the no start condition. If boiling hot fuel comes out, keep bleeding until you have a steady stream. If it now will restart you found your problem. Also if you are seeing that hotter than normal temp reading after it stalls bear in mind that the temp can go up 15 to 20 degrees when you shut off a hot engine. Here is a link to another post that tells more about the vapor lock issue. http://www.tahoeyukonforum.com/threads/2007-gmc-denali-stalls-after-towing.73312/#post-1013310

 

[puckhead]

OP: Any word?

I am in the process of wrapping my fuel lines right now. I attached a picture of the fuel line, just want to make sure I'm doing the right one. It also looks like there is a metal crossover to the other side of the motor. Is this correct?

Also noticed that some wire loom in the area behind the alternator was brittle and crumbled when I touched it is one that looks a bit melted. I recently replaced the alternator but could it overheat to the point of vapor lock?

 

[Ming15237]

I would think that a cracked block or blown head gasket would show one of several symptoms........water in oil, a cylinder misfire, low coolant level from combustion gases over pressurizing the cooling system, white smoke out the tail pipe, etc. But for overheating it will be due to low coolant level from the escaping/leaking coolant if block or head gasket is suspected.
Also ASE master tech since 1991.

I have seen failed head gaskets cause near zero coolant loss, yet cylinder pressure will over come the coolant system thus causing an air pocket that the water pump is incapable of pumping. Cranking the engine without the drive belt installed will quickly reveal a failed gasket or cylinder head. Blocks failing is truly an anomaly I have not seen on these motors, yet failed heads and gaskets are somewhat frequent.
In general white smoke exiting the exhaust is highly uncommon these and would require a major coolant leak to produce this type of result. Oil in the coolant would not likely cause an overheating condition because of the area the coolant is leaking into, this is also a fairly uncommon failure in my opinion.

 

[swathdiver]

On other GM engines, I've had a head gasket failure that blew into the radiator but not the other way around.

 

[muncie21]

I have an '09 Denali with the 6.2 and interested to hear what the issue is/was.