Fluctuating Coolant Temp, Normal?

bowhunter8 · June 22, 2020

Truck: 2019 (old body style), 5.3L, 4x4, 17,000 miles, towing and driving elevation:4000’-8500’

Trailer with Jeep: 5600lbs

Recently bought a tandem axle flat trailer and a wrangler to off-road. While towing a few months ago, I would notice the coolant temp would go from just under 210 to the green arrow line under moderate to heavy acceleration. The temp would stop there and then reduce a bit and hold between the green arrow line and 210. Once I crest the hill or let up on the acceleration, temp would be back to normal. I chalked it up to towing and truck being under load and didn’t dig into it deeper.

Now that’s its summer I’ve noticed the same thing happen when I’m not towing or hauling anything but am at freeway speeds under heavy acceleration or steep inclines. The coolant temp will do the same as the above.

Coolant is full. Trans temp stays between 190-200 while towing and around 190 while not towing.

Only thing I can think of is if the grill dampeners don’t open till I hit the green line and then once they do open and let a lot of air to the radiator, the temps reduces a bit and then all the way once the load on the truck is reduced. Then the grill dampeners close again and the cycle starts again on the next hill.

I’ve tried serval times to get the temp gauge to go higher than the green line when the outside air was 85 degrees and I really laid into the accelerator while towing but temp wouldn’t get past the green line (steep incline for 1-2miles, 3500rmps-4000rmps, 5600lb trailer, AC on)

Is this normal?

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CamGTP · June 23, 2020

Sounds normal to me.

You can hook up a scan tool and watch the actual temp if you wish. The coolant is probably getting into the mid 220's and the fans kick on to keep the temp steady. Seeing 200-220 degrees is normal in these trucks.

Bonus information here, if your truck has a 6 speed auto you can remove the inline transmission thermostat to drop your transmission temps by a decent amount. Unloaded on a 70-80 degree day on the freeway I dropped mine by 30-40 degrees. Haven't towed with it yet to see how much lower it keeps it with a load.

bowhunter8 · June 23, 2020

Sounds normal to me.

You can hook up a scan tool and watch the actual temp if you wish. The coolant is probably getting into the mid 220's and the fans kick on to keep the temp steady. Seeing 200-220 degrees is normal in these trucks.

Bonus information here, if your truck has a 6 speed auto you can remove the inline transmission thermostat to drop your transmission temps by a decent amount. Unloaded on a 70-80 degree day on the freeway I dropped mine by 30-40 degrees. Haven't towed with it yet to see how much lower it keeps it with a load.

Thanks for the info. I do have the 6 speed, what are your thoughts on removing the inline thermostat and warranty? Warranty is the main reason I have a non modded Silverado

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CamGTP · June 23, 2020

They will never know. It's a super simple thing to do. Takes about 30min taking your time and you aren't even removing anything. You are just flipping the piece inside the thermostat to make it flow fluid at all times instead of waiting until the fluid is above 185-190 degrees.

There are a few threads and youtube video's showing exactly what you have to do once the part is removed from the transmission.

truckguy82 · June 23, 2020

It’s normal, it takes a lot to overheat anything on these trucks

Edited June 23, 2020 by truckguy82

bowhunter8 · June 30, 2020

It’s normal, it takes a lot to overheat anything on these trucks

Sounds good, thanks.

Took it to the dealer yesterday and they said they hadn’t heard of a problem like I’m seeing. They took it for a driver and on hard acceleration they were able to get the temp to increase a bit and said it’s normal. Checked all fluid levels and they are normal

I’m betting most people don’t realize their temp gauge increases a bit (10-15 degrees) during heavy acceleration or when towing up hills and so it hasn’t been brought up to my local dealer

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truckguy82 · June 30, 2020

I was well aware of it

I boiled it down to coolant passages being so efficient at absorbing heat that as soon as your engine heats up it’s immediately transferred to the coolant

atleast that’s what I tell myself