03 1500HD overheating only while towing

[EvilWS602]

I drive an 03 1500HD 4x4 with 4.10 gears that has 230K miles on it. Truck does great when not towing even if I keep the pedal to the floor, but as soon as I hook to a trailer even with a light load, like 1,000 pounds, it starts to run hot. It runs 220 - 230 down the interstate at 60 - 70 mph turning 2k rpm and about pegs the gauge when I climb and incline.

I replaced the water pump about 60 - 80 thousand miles ago, the radiator, thermostat, and all the coolant just less than a month ago. The radiator is an Acdelco GM replacement. I put a 186 degree thermostat in it I believe. a couple years ago I removed the factory clutch fan and installed the newer factory dual electric fans in its place. but those do not come into play while the truck is moving down the road. They do their part by cooling the truck down while I am stopped.

I know it is a very hot summer here in Louisiana with temperatures reaching 100 degrees but why does is this only an issue when I hookup to a trailer?

Any help is greatly appreciated being that I've tried everything I can think of am I am still left scratching my head.

Clint

[00Silverado4x4]

Your fan should still be turning on when you are moving. Are you sure the fan are coming on and running at full speed at the correct temp?

[sahls01gmc]

I agree, your fans should be operating based on your engine temps, not whether or not you were moving down the road.

[Jsdirt]

If it's not puking coolant out the tank, it could very well be the notoriously inaccurate OEM gauge (if that's what you're going by) & sender - they've been known to show problems when none exist. Some other way of measuring actual engine/coolant temps should be used to verify.

 

If you've got an aftermarket temp gauge, then you might be needing a much cooler thermostat than what you've got in there now. Maybe a 160° for summer.

 

Another thing to check is your belt and tensioner - could be allowing belt slippage, spinning the water pump much too slow.

 

 

Just an FYI, I never had very much luck keeping my El Camino cool In Phoenix removing the OEM fan for electrics. Even if I left it on 100% of the time, the car would still hit 260° going through a drive-thru, and 220°-230° running down the highway. I fixed that problem by installing the OEM fan and a new fan clutch, removing the electric fan, and taking a sawzall to the core support, so my giant 4-core radiator was right out in the airflow 100%. Never hit over 195° after that, even towing with the A/C cranked.

[Doug_Scott]

Grab one of those bluetooth ODBII transmitters and install Torque on your Android cell phone, or use some other application that can talk to the bluetooth device you plug into the diagnostic port.

The software can be set to show you what the ECM is getting for the coolant temp. It is likely more accurate than the in dash gauge.

 

When you took the stock fan off, what happened to the shroud on the rad? Manufacturers spend a lot of money engineering cooling system air flow. Changing it by just removing what was there and sticking a couple of electric fans in place will not likely work as well.

 

Surprised no one has mentioned the transmission temps. The factory radiator is generally used to cool transmission fluid as well. Check the external trans cooler as well, if it has one. Make sure the fins are not bent over, and the airflow through it is sufficient.

 

Did the running hot start after the recent repairs, or were the repairs part of the ongoing fix for the running hot? Is this a gas or diesel engine? Has there been a tune applied to the ECM?

[Badass69]

I would still go after the rad or the water pump. Especially the pump. The fans don't need to come on above 40 mph... there is more air movement from the force of the truck than any fan could ever create. The factory e fans are a great upgrade over that junk clutch fan those trucks had. Look at it this way... his 1500hd is legal to tow 9900 lbs... a new 6.2 is what.. over 12000 lbs now. And they run e fans and don't overheat.... He stated he has the oem gm fans so they are not an issue.

 

Tranny temp is relevant as is the engine oil cooler. A person could remove both those from the radiator and simply run them to stand alone coolers.... but that is probably just a bandaid for something else.

 

I would still look hard at the water pump or even the lower rad hose. It might be collapsing but for 2 to do that and those are so short.. I doubt it.

 

Although for leaks and not overheating I went through 6 water pumps on my 05 1500HD in about a year... including the oem big dollar gm ones. Finally have one now that doesn't have something wrong with it.

 

Unless the op says otherwise because he or someone swapped it 1500HD's use the LQ4 with a 4L80E behind it just like the 2500HD and up trucks do.

 

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Edited August 4, 2015 by Badass69

[EvilWS602]

I might recall the truck getting slightly hotter towing before I swapped the radiator for an OE Acdelco HD. Only reason I changed it is because a tank cracked and was leaking. I changed both upper and lower hoses when I changed the radiator.

 

The overheating was becoming more of an issue bci was towing more often so I believe I had a 160 thermostat in it. My buddies and I could only come up with the conclusion that it was allowing to much water to flow not giving it time to cool off in the radiator. So I swapped it for a 186 and still same issue.

 

E-fans or fan clutch I belive is moot in this situation. Going 70mph down the interstate I should be able to pull the fans out of the truck and it not over heat, there's plenty of air flowing through the front of the truck. But they are OEM GM fans out of the newer trucks.

 

A couple of years ago I put in a autoparts shop water pump from O'Reilly's. But it obviously pushing plenty of water bc my heater house connection has broke a few times and it pushes out all the coolant in the matter of seconds. Also flushin out the coolant system lol.

 

Still stuck at square one....

[Doug_Scott]

The idea of coolant flow being too fast through the rad is usually associated to no thermostat, so the hole is wide open, no restriction at all. Some will say too high a coolant flow cannot create an overheating condition, but, I had a 351C in my 78 Mustang that without a thermostat would start running over 220 degrees after about 45 minutes of driving, and would continue to climb if I let it keep running. I put a Moroso water restricter into it (and that is exactly what that kit is for) and temp issue went away. That does not apply in this case though, you still have a thermostat in it. Just to clear up what appears to be a misunderstanding though, the thermostat does not hold the engine at a specific temp, it simply controls how quickly the engine gets up to operating temperature. A 160 thermostat will not stop the temp from running at 195 eventually.

 

I have heard the theory regarding a water pump causing overheating, but that was limited to the impeller slipping on the shaft. Traditional water pumps on engines are not positive displacement pumps, they are more like a fan running in water. Not the most efficient way to move the water, but is apparently good enough. They used to have different pumps for heavy duty cooling packages, and would not trust local jobber from supplying a heavy duty rebuilt pump in place of the standard pump. Not sure that is even relative anymore though.

 

The radiator has been changed, were all the plastic parts put back in? Referring to the bits that aid in airflow redirection or funneling. Is there a bug screen in front of the A/C condenser? Is the condenser plugged up with road crap and bugs? As stupid as it sounds, when you installed the factory radiator fans, did you verify the direction of the air flow from the fans when running? Make sure those fans are not pushing air through the rad. Don't just assume, it is stupidly simple to have it backwards.

 

The difference when towing to when not towing is load on engine and transmission. Double check trans temp, engine oil temp, and what the actual engine temp is as per the ECM. Would bring a quick end to this if the ECM is reading normal temps.

[EvilWS602]

Only plastic piece that isn't installed is the very top piece that goes to the grill and upper radiator support. It hasn't been installed for about three years though when I put a new grill on the truck. I did pull it out the scrap pile the other day so I can reinstall it just incase.

 

The fans are running in the proper direction and have been installed and operating fine for over two years.

 

Condenser is not clogged and no bug screen.

 

Trans temp and all other gauges read fine while towing.

 

The temp gauge has pegged out while climbing inclines and went into reduced power. Does that mean the ECM is also reading the same as the gauge? I will borrow my buddies scanner next time I tow and monitor it all through that to verify what my dash is reading.

 

I believe the problem is steadily getting worse though bc it is even doing it with light load now when it use to only be heavy loads. Also just the past couple of days the temp outside has been in the 100's and not towing anything with typical everyday driving the temp gauge has gotten to 225 degrees or so on my way home in the evenings but does fine in the mornings.

[EvilWS602]

Only other thing I thought of is that I have my heater hose bypassed at the fire wall. It started leaking at the beginning of the summer into my vents so I just bypassed it. We ruled that out from being part of the problem bc it is still before the water gets to the radiator to be cooled. Still stuck....

[Doug_Scott]

As long as you connected the two heater lines together it should not make any difference to the cooling system. It has no idea the heater core is not included anymore. That being said, you have however removed on of the ways to reduce engine temps. Is there a connection time-wise to the bypassing of the heater core and the higher than normal engine temps? Would not surprise me that GM was using the heater core as a small radiator and heater box was just dumping the hot air to atmosphere outside the cabin.

 

I am going in the assumption this is a gas engine. It was mentioned earlier in the thread to see if the coolant is being pushed out into the overflow/recovery tank. Is it? When the temp gets up to the point the ECM intercepts and tries to save things, pull over right away and lift the hood to check the overflow/recovery bottle. If you shut the engine off as soon as you stop, the temp will spike and should dump into the tank if the temp is truly that high. Or at the very least the hoses should be hard as rock if the engine is that hot. I am not sure where the ecm takes the temp from when it decides temp is too high. I would not be surprised that it monitors two sensors, and takes the worst case as being correct.

 

Whenever I ran into a engine that would overheat under load, it was usually either the fins in the rad were coming free from the tubes in the rad, or it was a timing issue (pre EFI), or transmission running very hot.

[EvilWS602]

This is a gas 6.0L. Only thing that came in the 1500HD's. I have not noticed the coolant boiling out yet but it only spikes on inclined and starts to cool back down on the decline and coasting so it comes out of the reduced power mode.

 

I bypassed the heater hose and connected the two together at the beginning of the summer. Now that the ambient temps are reaching and exceeding 100 it has been more apparent. I believe it won't be as much of an issue once temps outside finally drop. It it makes it that long before burning up lol.

 

And the new radiator fins looked good from the inspection before I installed and did not bend any during installation.

 

Tans Temps are good while towing....

[EvilWS602]

I guess I'll have my tuner check the timing bc we did some very miner tuning when we activated the factory e-fans.

[Badass69]

Hmm. If you are running with more advance and still have power enrichment delay enabled that could easily heat the truck up. Power enrichment delay holds the engine to stoich at wide open throttle and high rpm for a full minute. With that disabled among a lot of other changes but still the stock fueling tables I run 10 more degrees of spark advance across the board on LQ4's. They run great honestly even on 87 octane with no knock... because that's how terrible the stock tune is too. I have done e fans plus home made efilive custom tunes on 5 1500HDs now lol.

 

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Edited August 7, 2015 by Badass69

[Doug_Scott]

This is a gas 6.0L. Only thing that came in the 1500HD's. I have not noticed the coolant boiling out yet but it only spikes on inclined and starts to cool back down on the decline and coasting so it comes out of the reduced power mode.

 

I bypassed the heater hose and connected the two together at the beginning of the summer. Now that the ambient temps are reaching and exceeding 100 it has been more apparent. I believe it won't be as much of an issue once temps outside finally drop. It it makes it that long before burning up lol.

 

And the new radiator fins looked good from the inspection before I installed and did not bend any during installation.

 

Tans Temps are good while towing....

 

For whatever reason I read the topic as being 3500HD. Now that you mention a tune, when did the hot running start, before or after the tune? Do you have the ability to go back to stock tune to check engine temp when towing on highway? The fans may not work (you could just temporarily wire them up direct to battery) but they are not needed once truck is moving over 15mph.

[EvilWS602]

We did a very minor tune when we turned the fans on over two and half years ago. We really just adjusted a few things to try and help the mpg in that pig. I'll get my him and have him check the timing and the tune just to see. I was going to have him re-tuned it for some more ass after a few performance mods to get a little more grunt out of that turd, but I've grown tired of spending time and on money on that truck.

 

But to answer the question. Truck ran fine for 2 - 3 years after being tuned.