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

[rubicon1976]

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.

Screen shots from Torque:
1. Right before I came to a stop


2. Right after stopping

 

[swathdiver]

Have you ruled out a blown head gasket? Does your scan tool show misfires and fuel trims?

Have you tested the relays and fans to make sure they are running as they should?

Are you running Dexcool with a 50/50 mix with distilled water and did you properly flush the system?

Were all of the parts replaced with GM OE or AC Delco items?

Has the 100k mile service been done?

Is it somehow possible that this OBD adapter is causing a malfunction to your cooling system? Can you replicate the condition with the adapter off?

The transmission temps reveal that it appears to be in good form, well within specs.

 

[gpracer1]

As always you will have to be certain that you REALLY are running that hot.
You may have to install an analog temp gauge (not electrical) to co-witness these supposed temps.
I dont see why the truck would shut off unless it really is so hot that there is a vapor lock situation going on from boiling fuel. Maybe there is an electrical problem/battery/alternator/ignition switch, etc.
I would monitor voltage and analog temps when it happens again......especially if you can repeat the problem at will.

 

[intheburbs]

All good points by Swathdiver, and two additional things

- have you checked the cooling fins themselves, to make sure they're getting good air flow and not packed up with gunk - leaves, bugs, debris, etc?
- Have you purged/burped the cooling system to make sure all the air is out of it?

I'd be really worried about the all-aluminum 6.2 getting that hot. It's more of a hot-rod motor than an HD towing-type motor like the cast-iron block 6.0.

If you truly are getting that hot, it's not normal. I pull an 8600-lb travel trailer, and the only time I've seen temps anywhere near that high was on long steep climbs like the Eisenhower Tunnel approaches. And it was the transmission seeing most of the heat, not the engine. Trans was as high as 241°, but the engine was staying around 230-235°.

 

[kbuskill]

I would wrap the fuel lines, up near the engine/transmission, including the fuel rails with a heat reflecting wrap, like the foil backed fiberglass stick on wrap for starters.

This is a very simple thing to do and should rule out vapor lock as the issue.

Conversely, since you know how to make it act up, you could try relieving the fuel pressure at the fuel rail through the Schrader valve when it shuts off to see if it will start again without waiting the hour for it to cool down. Just be careful as you will be spraying gasoline out onto a hot engine. Perhaps using a rag would eliminate some chance of a fire.

 

[Doubeleive]

When you say radiator fans, do you mean just the plastic fans or the motors as well?, Plastic fans don't ever really wear out unless they somehow cracked so you could just do the motors and use the same fans. Have you stopped and popped the hood and made sure the fans are going when it starts to get hot?. What radiator did you use?

 

[puckhead]

I am having the exact same issue that you are having. Coincidentally in Divide, CO also, specifically coming up the pass to Woodland Park. I'm about to blow this thing up. Nothing has seemed to help.

@swathdiver: How do I go about checking for a head-gasket issue? There doesn't seem to be any contamination in either the coolant or the oil.

Everything else checks out and I don't want to throw money at it to hopefully fix some unknown problem.

 

[swathdiver]

I am having the exact same issue that you are having. Coincidentally in Divide, CO also, specifically coming up the pass to Woodland Park. I'm about to blow this thing up. Nothing has seemed to help.

@swathdiver: How do I go about checking for a head-gasket issue? There doesn't seem to be any contamination in either the coolant or the oil.

Everything else checks out and I don't want to throw money at it to hopefully fix some unknown problem.

Mechanically, use a compression test gauge to check each cylinder initially. For a more thorough examination, a leak down test. Sometimes just looking at the spark plugs is enough.

Is there a simpler way fellas?

 

[kbuskill]

As James said... compression test and look for any plugs that look like they have been steam cleaned.

 

[kbuskill]

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.