Duramax Overheating

[logger73]

So, I am taking my family on our one week summer vacation into the California Sierra Nevada Mountains and my 2004 GMC Sierra Duramax 2500 HD redlines climbing several of the grades. I have the LB7 motor and I am pulling right at 15,000 lbs of 5th Wheel Toyhauler. (Right at the edge of maximum for my truck) http://www.thumpertalk.com/forum/images/smilies/banghead.gif My question is this: Since I am careful to pull the grades at moderately low speed, shouldn't the coolant system be adequate for the kind of weight I am pulling. One of the 'old boys' in the campground suggested I take out my radiators and hose them off due to potential plugging by bug debris and dirt?Is there an aftermarket piece of equipment that would assist with the overheating? Any info would be appreciated. Thanks for assisting a rookie.

[lb7lbz]

when you say redlines how do you mean? the redline on the temp. gauge or the truck didnt shift until the redline on the tach.?

[logger73]

Sorry, by redline I meant that the coolant temp gauge hit 260 degrees at the redline. My tach reads fine.

[Duramaster]

Is your fan clutch working? You should have heard the fan way before the 260 degree mark.

[Mark Rinker]

Welcome aboard! You are in the right place to solve your overheat problem...running moderately hot in the mountains while towing is to be expected, however 260F sounds like you are on the ragged edge of what would be expected. Your LB7 has plenty of power and cooling available to handle that load...something is amiss, or the conditions you encountered were out of range (extrememly hot day, heavy right foot, dragging brakes on trailer...hmmm)

1) What ground speed are you maintaining when the overheat occurs? What was the outside temperature at that time?

2) Are there any power mods to your truck? If so, what brand and what power level do you run when you tow?

3) A healthy fan clutch, and clean cooling stack is your best defense in these extreme situations (summer heat/mountain elevation and grade/towing heavy) good news is the clutch on stock LB7s comes in early (around 230) and stays on late. You should have heard it roaring during most of these overheat events. If not, you'll need a new one - however the new OEM ones have the same GM part#, but aren't as effective, utilizing higher engagement temperatures, and won't perform as well as your original model. You might consider digging around boneyards and recyclers to see if you can find a used one off a 2001-2004.5 wreck that is still in good operating condition...

4) If you still have original thermostats in your truck, now would be a good time to replace both - with GM OEM parts. Could be one is sticking partially shut and impeding coolant flow.

5) De-bugging the cooling stack and a cooling system flush with new DexCool is always a good idea, if you haven't done it recently. Search the forums here for more information.


Good luck!

[logger73]

Thanks for the responses. To answer specific questions:

1. The ground speech has varied. When I noticed her heating up, I dropped the speed from 45 mph to around 30, with little improvement. I assume this has to due to minimized air flow, outside air temp was in the high 70's.

2. I do run an Edge Juice w/Attitude Module, and when the overheating started in was in Level 1, when it started heating up, I dropped to '0' which is supposedly stock.

3. Not sure about the backup fan clutch assembly. The fan didn't seem to be turning on when expected so, I do suspect it is part of the problem.

[Mark Rinker]

Sounds like the problem all right. Try to find an older LB7 era clutch if you can. If the problem persists, remove the Edge box as a test - although Level 0 should be stock fueling, anyway...

I'd clean the cooling stack and replace thermostats if you are over 100K miles on them.

Good luck!

[More Power]

The sound of an engaged fan is unmistakable to those with more or less normal hearing. The fan-clutch is perhaps the single most important component in the cooling system, and it is not a lifetime part.... It can fail after a few years of service. I talked to a 2004.5 LLY owner just a couple weeks ago whose truck was overheating. His truck's fan-clutch wasn't engaging.

With a correctly operating cooling system, the LB7 was the coolest running Duramax because of less aggressive emissions control.

In addition, managing the engine to produce no more than ~2400-2500 RPM while pulling hard will help to limit engine temperatures - largely because the stock turbo will be operating in a more efficient range than it will be at higher engine RPMs.

Jim

[markelectric]

If the cooling stack is plugged the lower ammount of air flowing thru will not set the fan clutch at the proper time. I would clean the radiator first........