GMC 2008 diesel overheating

2008 GMC diesel 2500 towing Jay co 5W. I know my weights are good, but while coming to CA in June the truck almost overheated several times. All were long upgrades and hot weather. The first time I was going too fast and did not down shift, so that was my fault. the next was coming out of Reno on 395 I downshifted and went real slow, I had to turn the AC off to keep the temp down. The same happened coming out of Susanville on Hwy 36. I have been told that it shouldn't overheat. I am not sure what I am doing wrong. I am not sure of how to use the manual shifting so maybe I need an education on that. Checked on the diesel forum but the only thing I saw there was to pull the whole front of the truck off to clean the fins on the radiator.
Are there any other GMC 2008 owners out there that could give me some advice?

It sounds like your radiator is clogged with dirt. Last time it happened in my diesel it cost me $250 to have the radiator flushed of dirt. Dirt accumulates on the outside of diesel radiators and that reduces it's cooling ability.

Clearly, the issue is heat transfer.  The engine is generating more heat than the radiator can dissipate.  Possible causes include low coolant levels and dirty radiator on either inside or outside.  #1 is easy to fix.  #3 may be fixed with a good flush from a garden hose if you can get good access to the radiator.  At 10 years old, it may be due for a good old fashioned flush and fill.

I doubt is is serious unless it is ignored.

Thanks for the replies. I will have the radiator checked. One more question on the exhaust., The truck has the big tip on the exhaust pipe which is for cooling the exhaust. I noticed a slight kink in the tail pipe in front of the tip. I don't know if it should be that way or not. Could that cause it to overheat? Cathy

What were your temperatures?

What do you mean almost overheated?

DIC messages?

How fast was really slow and what was your rpm when going real slow?

Mud Puppy said:

The truck has the big tip on the exhaust pipe which is for cooling the exhaust. I noticed a slight kink in the tail pipe in front of the tip. I don't know if it should be that way or not. Could that cause it to overheat? Cathy

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It could contribute depending on how bad the kink is. One of the quickest ways to make a diesel overheat with a manual transmission is to drive in too high a gear for the load or "lugging" the engine.

The first time when I was not paying attention I got a DIC message. so pulled over to let it cool off. It never blew water out I just watched the temp gauge, when it started rising rapidly from the normal temp. I turned the AC off and heat on.
The kink is not bad and I am not sure if it came that way or not. One side has a rectangular stamp of some kind that looks like it came that way. the other side is where it looks like a small kink in the pipe. It is not a manual transmission but does have the manual selector which has I think 6 gears I can shift it through.
I think not more than 30 MPH and mostly 20 MPH I do not remember what the RP M's were or what gear I had put it into. most likely 3rd or 4Th. I now know that I should maintain 2500 or so RPM.

Cathy, I have a 2006 GM diesel and, when towing (especially in hot weather) I have had to keep a close eye on the engine temps on long uphill hauls.  You asked about using the manual shifting, and that's what I do in those cases.  You might try this the first time just when you're driving just the truck and not towing so you can get a feel for it.  Simply shift from D to M.  Your truck will continue running in the gear you're already in.  On the gear display on the steering column you will now see the numbers 1 - 6 and it will show which gear you are currently in.  The buttons for shifting up or down are on the shift handle.  If yours are like mine, they're just two buttons; one with an up arrow, the other with down.

So how do you pick what gear to be in?  I do it mostly by feel.  First, I don't press harder on the gas pedal.  I just let the truck pick the speed it will go.  I watch the RPMs and if they drop below 2000, I downshift while continuing to hold the gas pedal in a moderate position.  For most grades I end up going 30 - 40 mph at around 2000 rpm.  My temperature gauge will still sometimes go above the midpoint, but shortly after that I hear the engine fan come on and and the temperature drops back down.

Although the Tow/Haul mode's engine brake is great for many downgrades, if you get on a steep one, using the Manual shift selection to help keep your speed down is also a good way to keep your rig under control. 

Hope this helps.  Happy hauling.

Thanks so much for the advice.  Mine seem to be the same as you described. I have played with the manual shift a bit now. I was just never sure which gear it should be in. I will now watch the RPM's I have only had the truck a year and this was the first time in the mountains. But I plan to do ID in Sept. so I better figure it out. I will have the coolant and radiator looked at though. I had a gas vehicle before this and a light TT that I took to the mountains a lot. This is a different story and I thought would be easier. Thanks again.

Did you hear your engine fan at all? It should have been roaring loud if you were getting hot.

If you didn't hear it, I would sure get it checked out.

I am not sure about the fan. that was in June and my memory does not serve me well. but I will have the fan checked. Thanks for the input.

catblaster said:

It could contribute depending on how bad the kink is. One of the quickest ways to make a diesel overheat with a manual transmission is to drive in too high a gear for the load or "lugging" the engine.

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Will, do diesels have coolant thermostats like gassers?

When was the last time the coolant was changed?

I have only had the truck for a year an do not know when the coolant was changed. I am going to have that looked at also. Thanks

Rene T said:

Will, do diesels have coolant thermostats like gassers?

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Yes, they do.

Rene T said:

Will, do diesels have coolant thermostats like gassers?

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yes sir

When my Ford F350 started acting like that the clutch fan had failed.  The truck was new to me and I didn't even know what it was supposed to sound like.  Once it was fixed, on bigger pulls it sound like a helicopter was taking off under the hood.

Any update?

Well I don't know if my overheating problem is fixed or not. I took it in and they suggested changing thermostats. So did that. I am stationary right now so don't drive it so much. Then 2 days later when I did drive it my check engine light came on and it was running real rough. So I have spent the last week trying to get that resolved. I am 90 miles from a dealer so trying to find someone to work on it has not been easy. Got the codes read, which indicates the #3 and #8 injector wiring harness. I am a workamper so it takes longer to get things done. Found a guy that is going to check voltages to see where that leads and also made an apt. with the dealer just in case.
I have got to say this truck has been nothing but trouble since I bought it. I will try to keep you posted. Thanks Cathy

I'm on my 5th diesel and never once had an overheating issue. These trucks are made to work hard and the cooling systems are very robust. I remember getting stopped in traffic in Atlanta one time in 95 degree weather for three hours. We sat the with engine idling with the a/c on and the engine temperature actually dropped. Tons of people had to turn their cars off and swelter because the gas engines were overheating. It will end up being a thermostat or fan, unless your radiator is fouled outside with dust or weed seeds or something similar. I had an 06 Ford with the 6.0 engine that the "check engine" light came on at 60,000 miles. Almost always this is an environmental sensor problem, not injectors or other mysterios high dollar items. The truck would run a little rough when cold, then did just fine after warming up. I finally figured out it was an exhaust gas recycle valve sticking, but I never changed it. Truck ran great until I traded it off at 150,000 miles. When I worked for AOL internet as a troubleshooting tech, they would tell us for any problem to advise people had a "virus" as a starting point. Only in one case in all that time did I find a virus a source of someone's computer problem. Now it seems for diesels the first troubleshooting advice is "dirty injectors" or wiring harnesses. Like I said, I've had 5 diesel trucks, and two diesel tractors. Never had an injector issue or overheating. Just saying, I hope you share the resolution to your problem and don't have to spend a lot of money.