Over Heating

Larry Rinehart · July 18, 2023

My 2003 Sierra HD crew cab pickup overheats when I pull my toy hauler, especially in hilly terrain. I bought the truck new, have take care of it, and it only has 80,000 miles on the odometer. I pull a small toy hauler with motorcycle in the back. It overheats on hills and when going slow in traffic. And, the AC only works well when I’m traveling at highway speeds. The engine is solid, always changed oil at 3k and it never uses a drop of oil. My question is: can I do anything to fix the overheating problem, bigger radiator, etc? I’ve had the current radiator flushed and refilled accordin

hiking_mike · July 18, 2023

I have a pair 07 2500's. I started noticing the transmissions would get close to the max of what I felt confortable with.

We opened up the 'stack" or I mean We removed the radiator. What I first noticed is that the holes in the various devices as air passes through get smaller and smaller. The radiator is last, and has smallest, AC condnsor is largest.

So bugs and debris wil pass through condensor, intercooler, then in to the radiator, where they get stuck and block air flow.

Removing the radiator on both trucks, i noticed a lot of dead bugs, road grime, and debris. So using a lot degreasor and water hose, it took some effort to clean the raditor. I also u sed a power washer on low pressure making sure not to do a "sweeping action" in order to keep from messing up the fins.

Then spraying what was left in the truck, the intercooler and condensor from back to frount, this cleand the intercooler and condensor, and transmission cooler.

This made a HUGE difference in transmission and engine temps. I took a 7,000 camper all the way to Key West in July -August time frame.

I went from having to slow down to about 60 and lots of stops to allow wverything to cool off to having no issues at all.

hiking_mike · July 18, 2023

Make sure your transmission is in Tow Mode, I noticed in heavy traffic, and one time I forgot to activate and was suprssed how hot the transmission got so quickly. I have had to repalce the little push button that goes on the shift lever, as the wire shorted out.

Removing the radiator was not too difficult. kind of a tight fit getting out.

newdude · July 18, 2023

1 hour ago, Larry Rinehart said:

My 2003 Sierra HD crew cab pickup overheats when I pull my toy hauler, especially in hilly terrain. I bought the truck new, have take care of it, and it only has 80,000 miles on the odometer. I pull a small toy hauler with motorcycle in the back. It overheats on hills and when going slow in traffic. And, the AC only works well when I’m traveling at highway speeds. The engine is solid, always changed oil at 3k and it never uses a drop of oil. My question is: can I do anything to fix the overheating problem, bigger radiator, etc? I’ve had the current radiator flushed and refilled accordin

Fan clutch bad? I seem to recall a string of these in the 01-07 range that had overheat issues due to bad fan clutches. If it can't engage and ramp up the fan speed, its not going to pull in extra air across the radiator in lower speed driving.

Edited July 18, 2023 by newdude

Larry Rinehart · July 19, 2023

Thanks for the helpful replies. I cleaned the bugs from the radiator today, only to find there are four radiators of varying size. The biggest and closest to the fan is the engine coolant, directly in front of it, and slightly smaller, is what I assume to be the transmission radiator. In front if that and much smaller is a radiator of unknown purpose. Off to the side and even smaller is the power steering radiator. Interesting. I will take the truck to the shop to have the fan clutch checked. And yes, I always tow in tow mode. Again, thank you all for the help. Larry Rinehart

vucelick · July 19, 2023

In addition to above posts check thermostat, and make sure the water pump is functioning properly. Have you always run dexcool antifreeze? I remember initially dexcool was not comptible with other coolants, leading to corrosion and seal issues.

Edited July 19, 2023 by vucelick

newdude · July 19, 2023

33 minutes ago, Larry Rinehart said:

Thanks for the helpful replies. I cleaned the bugs from the radiator today, only to find there are four radiators of varying size. The biggest and closest to the fan is the engine coolant, directly in front of it, and slightly smaller, is what I assume to be the transmission radiator. In front if that and much smaller is a radiator of unknown purpose. Off to the side and even smaller is the power steering radiator. Interesting. I will take the truck to the shop to have the fan clutch checked. And yes, I always tow in tow mode. Again, thank you all for the help. Larry Rinehart

Looking at the grille of the truck, the vertical mounted one on the driver's side is power steering, the rectangle in the middle on that "A" brace is transmission, behind that is the AC condenser and then last is the radiator.

Larry Rinehart · July 19, 2023

Thanks. I had no idea.

Larry Rinehart · July 19, 2023

Is there anyway to figure out if the clutch fan is working right, or should I leave that to the shop?

hiking_mike · July 19, 2023

If you watch your transmission temp guage, I believe about 185 you should begin to hear the fan clutch engage until the temp drops. Forgive me, since I removed the radiator and cleaned, I dont have the issues I used to and forgot the temps it used to kick in.

You may hear the fan clutch on a cool damp morning for a few minutes or so.

As for the cooling "stack" its nickname is called stack sometimes due to all the cooling devices mounted in succession.

It the "radiator looking thing" is your intercooler. This cools the turbo charged airflow before it goes into intake of the engine. .

The only way to really clan the radiator is to remove it. You are not going to really blow water from back towards the front very well at all.