Strange overheating issue

[johnswie]

I have an ongoing overheating issue that is stumping me. The needle on my gauge will go up to 5/8-3/4 hot, stop and then fall back down to about half (I don’t have actual degrees, just tick marks). I’m assuming when it stops then drops, this is when the thermostat has fully opened. But I have a brand new 180 AC Delco, so not sure why it would get so hot. Also a partnering issue I have is that coolant is being forced into the overflow tank but doesn’t return back to the radiator. I had it checked for a blown head gasket and it came back with no signs of this (which it shouldn’t because the motor was rebuilt a few years ago). I have no known leaks. Should I get the radiator pressure tested? If anyone has experienced this I’d be appreciate hearing your input. I’m stumped.

 

[fast 99]

Gauges in these vehicles are at best indicators. Buy a cheap infrared gun and see what the actual temp is. Some mechanical gauges are much more accurate. Where the sender location is also affects the reading. If in the cylinder head reading will be higher by as much as 20 degrees than the thermostat. Really wouldn't worry about it provided it's not pushing coolant out.

 

[johnswie]

Gauges in these vehicles are at best indicators. Buy a cheap infrared gun and see what the actual temp is. Some mechanical gauges are much more accurate. Where the sender location is also affects the reading. If in the cylinder head reading will be higher by as much as 20 degrees than the thermostat. Really wouldn't worry about it provided it's not pushing coolant out.

That makes sense, I’ll try that. But it is pushing coolant out. Each time I drive it, the radiators a little lower. Maybe I’m over filling it? I’ve been filling it up to the filler neck.

 

[gmbellew]

I have a new AC Delco 195 degree thermostat in my 1990. the cluster gauge looks like 230deg when it opens up full for the first drive of the day. but the actual temp at the thermostat housing is about 208 based on the ECM coolant temp sensor. it does seem to open quicker if it has been driven somewhat recently.

 

[fast 99]

I have a new AC Delco 195 degree thermostat in my 1990. the cluster gauge looks like 230deg when it opens up full for the first drive of the day. but the actual temp at the thermostat housing is about 208 based on the ECM coolant temp sensor. it does seem to open quicker if it has been driven somewhat recently.

The initial opening temperature can sometimes be higher until the system temp equalizes.

 

[F-64]

Yeah, you may be getting exhaust gasses in your cooling system. Get a test kit. Autozone has the test kit as a rental I think. You just have to buy the fluid.
I've had this exact problem way too many times on different vehicles.
You would get bubbles in the reservoir even when the coolant was cold. The exhaust bubbles in the system throw your temp gauge between hot gasses and warm coolant.
You may be able to use a household carbon monoxide detector at the mouth of your radiator cap to detect exhaust gasses as well.

https://www.autozone.com/loan-a-tools/loaner-blown-head-gasket-tester

https://www.autozone.com/test-scan-and-specialty-tools/block-tester-kit/p/oemtools-combustion-leak-detector-fluid-8oz/391381_0_0

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[AuroraGirl]

I have an ongoing overheating issue that is stumping me. The needle on my gauge will go up to 5/8-3/4 hot, stop and then fall back down to about half (I don’t have actual degrees, just tick marks). I’m assuming when it stops then drops, this is when the thermostat has fully opened. But I have a brand new 180 AC Delco, so not sure why it would get so hot. Also a partnering issue I have is that coolant is being forced into the overflow tank but doesn’t return back to the radiator. I had it checked for a blown head gasket and it came back with no signs of this (which it shouldn’t because the motor was rebuilt a few years ago). I have no known leaks. Should I get the radiator pressure tested? If anyone has experienced this I’d be appreciate hearing your input. I’m stumped.

could also be your sending unit is not proper to your gauge

 

[Matt69olds]

Sounds like you have an air pocket in the cooling system.

Before doing anything, raise the front of the truck. Remove the radiator cap, top off the coolant. Let it sit overnight with the cap off, gravity will naturally force out any air

 

[johnswie]

Sounds like you have an air pocket in the cooling system.

Before doing anything, raise the front of the truck. Remove the radiator cap, top off the coolant. Let it sit overnight with the cap off, gravity will naturally force out any air

Thank you, I’ll try this!

 

[johnswie]

Yeah, you may be getting exhaust gasses in your cooling system. Get a test kit. Autozone has the test kit as a rental I think. You just have to buy the fluid.
I've had this exact problem way too many times on different vehicles.
You would get bubbles in the reservoir even when the coolant was cold. The exhaust bubbles in the system throw your temp gauge between hot gasses and warm coolant.
You may be able to use a household carbon monoxide detector at the mouth of your radiator cap to detect exhaust gasses as well.

https://www.autozone.com/loan-a-tools/loaner-blown-head-gasket-tester

https://www.autozone.com/test-scan-and-specialty-tools/block-tester-kit/p/oemtools-combustion-leak-detector-fluid-8oz/391381_0_0

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Interesting. Thanks for the the links, I’ll look into this!