2017 silverado overheating while driving and normal at idle

[ChrisM24]

So I have a 2017 silverado 5.3 with 102,000 miles and for some reason i cant figure out my truck overheats when i drive or put the pedal to move it over heats but at idle its back to normal.. I have put 2 thermostats in a temp sensor and flushed and filled the rad from the hose method so there would be no bubbles or air in the system.  Has anyone had this issue and could give me some pointers?? Theres no leaks anywhere the rad is full of fluid new thermostat new temp sensor im just at my wits end

Edited June 28, 2022 by ChrisM24

[CamGTP]

Define overheating.

 

How hot is it actually getting?

[ChrisM24]

If i keep my foot on the gas driving for say 1 minute or 2 it will peg out hot. Or if i floor it for a few seconds it will peg out hot unless i let off the gas and it will cool down some. It stays over 210 the whole time for sure. So i have to drive on and of the pedal to keep it from getting to hot

[CamGTP]

Either the water pump can't keep up or the radiator is lacking flow.

 

That is what I'd be looking at.

[ChrisM24]

Do you think the water pump went bad but just never leaked water? Ive never had that happen before and the rad i dont know what would cause it to not flow this whole thing came on a few weeks ago before that everything worked fine

[ChrisM24]

When i did all that before it seemed to work ok. It really didnt overheat but after awhile i took the cap off one morning to top off the fluid and ever since then its back to getting hot. I put a new cap on yesterday but it made no change. Has any of this happend to any of you? I could really use some help.

[rlcole321]

Check cooling fan operation, if fans are coming on, then could be a minor head gasket leak, look for "steam sludge", pull the oil filler cap and look for "Chocolat sludge" on the cap.  If not evident, still could be head gasket problem.

[ChrisM24]

It could be. Ive checked the oil and its not milky im not loosing antifreeze theres no leaks or anything dripping on the ground. I do know that when i cut my truck off my fans will run for alittle while after i cut the truck off. 

[stu_pidasso]

When you refilled the cooling system, which coolant did you use? And did you bleed air out of the cabin heater coil? 

In your idling, driving, and revving experiments, does the coolant level drop at all? Are you losing coolant?

 

On 6/26/2022 at 10:37 AM, ChrisM24 said:

Do you think the water pump went bad but just never leaked water?

A water pump doesn't have to leak to be bad. The impellor can, and has, spin/crack off the shaft and not pump anymore. I agree with CamGTP, if you're positive you used the right coolant, and you properly bled the entire cooling system including the heater core, then something is prohibiting the coolant from being pumped, or allowing it to dump the heat. The rad is easy to check, pull off the supply and return hoses, and you can check for communication, water goes in, water goes out, but that does not guarantee it can move the right amount of coolant through it, ie proper flow rate. 

Edited July 2, 2022 by stu_pidasso

[ChrisM24]

I agree. Im changing the water pump right now. When i drained the fluid out the section of the reservoir that says rear still has fluid in it. Isnt it all supposed to drain out when you take the drain plug out??

[ChrisM24]

2 hours ago, stu_pidasso said:

When you refilled the cooling system, which coolant did you use? And did you bleed air out of the cabin heater coil? 

In your idling, driving, and revving experiments, does the coolant level drop at all? Are you losing coolant?

 

A water pump doesn't have to leak to be bad. The impellor can, and has, spin/crack off the shaft and not pump anymore. I agree with CamGTP, if you're positive you used the right coolant, and you properly bled the entire cooling system including the heater core, then something is prohibiting the coolant from being pumped, or allowing it to dump the heat. The rad is easy to check, pull off the supply and return hoses, and you can check for communication, water goes in, water goes out, but that does not guarantee it can move the right amount of coolant through it, ie proper flow rate. 

When i flushed it the first time i didnt bleed the heat coil. To be honest i didnt even know about that or where to do it. As far as loosing coolant goes my tank has been just under the full line this whole time so i assumed it wasnt flowing and im using orange antifreeze mixing half and half concentrate

[stu_pidasso]

7 minutes ago, ChrisM24 said:

When i flushed it the first time i didnt bleed the heat coil. To be honest i didnt even know about that or where to do it. 

 

Well, don't go tearing apart the water pump and replacing it right now. This is a huge step that you missed the first time around that can cause exactly what you're experiencing. In order to bleed the heater core, the best way is to start your truck and set the heat and fan speed to high, as high as it will go, and let her rip for a few minutes. Air locking a closed loop can do exactly what you have going wrong. 1AAuto's YouTube has a lot of GM content, and has videos on how to bleed the system properly. I know its a GMT900, but the concept is the same, and the engine set up is mostly the same. Do it right this time, and if you're having trouble still, then start working it. 

 

18 minutes ago, ChrisM24 said:

I agree. Im changing the water pump right now. When i drained the fluid out the section of the reservoir that says rear still has fluid in it. Isnt it all supposed to drain out when you take the drain plug out??

 

Nah, there will always be pockets and areas of the cooling system that do not drain out even though everything is higher than the drain. Old Honda D series engines rads sit way lower than the block, but when you drain the rad the block is mostly full. Makes for a refill that requires care. I would personally use Dex-cool, I try not to screw around with coolants and just buy it right from the dealer. Your owners manual should tell you how much volume you need for coolant, if it wants 10L, and you put in 7L and the reservoir is full, well... 

[ChrisM24]

2 minutes ago, stu_pidasso said:

 

Well, don't go tearing apart the water pump and replacing it right now. This is a huge step that you missed the first time around that can cause exactly what you're experiencing. In order to bleed the heater core, the best way is to start your truck and set the heat and fan speed to high, as high as it will go, and let her rip for a few minutes. Air locking a closed loop can do exactly what you have going wrong. 1AAuto's YouTube has a lot of GM content, and has videos on how to bleed the system properly. I know its a GMT900, but the concept is the same, and the engine set up is mostly the same. Do it right this time, and if you're having trouble still, then start working it. 

 

 

Nah, there will always be pockets and areas of the cooling system that do not drain out even though everything is higher than the drain. Old Honda D series engines rads sit way lower than the block, but when you drain the rad the block is mostly full. Makes for a refill that requires care. I would personally use Dex-cool, I try not to screw around with coolants and just buy it right from the dealer. Your owners manual should tell you how much volume you need for coolant, if it wants 10L, and you put in 7L and the reservoir is full, well... 

roger that. Ill do some looking up on there and do my best. Ill keep you posted when i get done and see if it worked.

[CamGTP]

Coolant flows through the heatercore all the time, there really isn't a special way to bleed the system.

 

I run it up to temp with the expansion tank cap off, turn it off for a few minutes, let it bubble, add coolant and cap the system. Done water pumps on many GM trucks without an issue.

[ChrisM24]

41 minutes ago, CamGTP said:

Coolant flows through the heatercore all the time, there really isn't a special way to bleed the system.

 

I run it up to temp with the expansion tank cap off, turn it off for a few minutes, let it bubble, add coolant and cap the system. Done water pumps on many GM trucks without an issue.

So you don’t actually have to bleed the heater core?