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Overheating?

Tiny
TULPA
  • MEMBER
  • 2007 CHEVROLET SILVERADO
  • 4.8L
  • V8
  • 4WD
  • AUTOMATIC
  • 237,000 MILES
I flushed the heater core, changed the water pump and thermostat. My heater only works for a short time before blowing cold and it starts to overheat. Is my heater core bad? I don't have any leaks that I can find.
Tuesday, November 29th, 2022 AT 5:29 PM

14 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,489 POSTS
Hi,

If the heater core was bad, you wouldn't get heat at all. Since the engine is overheating, I have a feeling either there is air in the cooling system preventing the coolant from flowing or you have a faulty head gasket pumping air into the cooling system.

First, when the engine is cold, open the radiator cap and make sure the radiator is full. Oftentimes, people check the overflow reservoir only.

Next, if the radiator is full, again with the engine cold, leave the rad cap off and start the engine. See if the coolant bubbles or shoots out.

Take a look through this link as well. See if anything mirrors what you are seeing.

https://www.2carpros.com/articles/head-gasket-blown-test

Let me know what you find or if you have other questions. Also, let me know how the cooling system was bled when you refilled it.

Take care,

Joe
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Tuesday, November 29th, 2022 AT 8:54 PM
Tiny
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To get the air out I raised the front end, opened the Reservoir and let it get to operating temperature (210) squeezed the radiator hoses. No air bubbles were visible. I don't believe I have a bleeder valve. I do not have a radiator cap, just the reservoir. My oil looks fine, no milky residue. No smoke from the exhaust. Both upper and lower radiator hoses are not. Sitting in my driveway last night the temperature gauge was going up to about 220 then back down to 210. Temp only climbs when idling. A faulty temperature sensor wouldn't cause this. I do have a small oil leak which appears to be from the valve cover gasket.
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Wednesday, November 30th, 2022 AT 6:56 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,489 POSTS
Hi,

I attached what I have for refilling the coolant after draining everything. I do have a question. The vehicle came with DexCool coolant from the factory. By any chance, did you mix a different type of coolant with it? Also, if I recall, there is an air bleed pipe between the cylinder heads.

See pics below. The first pic shows the hose that runs from the radiator to the pipe. That is disconnected when coolant is added to allow air to exit.

Also, the last pic is what I have for the bleeding procedure. Let me know if it helps.

Take care,

Joe

See pics below.
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Wednesday, November 30th, 2022 AT 6:09 PM
Tiny
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  • 53 POSTS
This is very helpful. I didn't drain or fill it correctly. It also makes sense. When I flushed the heater core a few months ago I didn't drain the system. I added the coolant that the auto parts store suggested which does not say Dex Cool on the bottle. So, I probably mixed 2 different kinds which is why it worked fine for a few months? He is a pic of the coolant I used. It the wrong kind?

I will follow the guide you have provided. And I might as well flush the whole system since i'm draining it again.
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Thursday, December 1st, 2022 AT 6:14 AM
Tiny
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Hi,

Is there anywhere on the coolant bottle that indicates what it can be used in conjunction with?

I ask because if the wrong type is mixed, it can cause the DexCool to jell and cause things to plug up.

Let me know.

Joe
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Thursday, December 1st, 2022 AT 2:00 PM
Tiny
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It says it is compatible with other extended life coolants but doesn't mention anything specific.
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Thursday, December 1st, 2022 AT 2:42 PM
Tiny
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Hi,

If there is an 800 number on the bottle, contact them and ask if that is compatible with DexCool. If it isn't, chances are this is the problem.

Let me know.

Joe
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Thursday, December 1st, 2022 AT 9:10 PM
Tiny
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I called and they said it is Dex Cool it just doesn't say that on the bottle because the patent has expired. I'm going to flush it all out again today after work. I've noticed the new coolant is already looking dirty. I'm wondering if my radiator is clogged and or rusted inside.

I still don't understand why the heater starts blowing cold when the temperature goes past the mid-point (210).
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Friday, December 2nd, 2022 AT 8:42 AM
Tiny
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After driving for about an hour I turned the truck off and then turned the key (not enough to start it) and the temperature gauge kept going up until I started the truck, and it went back down.

I used my scanner, and this code came up

When I switch the heater to recalculate it goes cold. Switch it back and it's hot again.

Now only one of te heater core hoses is getting hot the other is room temp.
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Friday, December 2nd, 2022 AT 2:03 PM
Tiny
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Did the heater hose concerns start after draining and refilling the cooling system? Also, the code you have above is related to the cooling fan voltage. Do you hear the fan turn on?

The idea that the temperature gauge went up with the engine off is because the coolant circulation stopped. Once you restart it, the coolant begins to circulate again, and the temp will go down.

Let me know if the P0693 is still present. For some reason, it isn't listed for this vehicle in my manual.

Take care,

Joe
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Friday, December 2nd, 2022 AT 10:04 PM
Tiny
TULPA
  • MEMBER
  • 53 POSTS
It started overheating in the summer. Thats when I noticed a coolant leak. The heater core hose quick disconnect had a crack in it so I replaced it. Decided that would be a good time to flush the core. Very little debris came out of it. After that it didn't overheat for about 3 months. I would check it periodically. Both core hoses would get hot. Now only one get hot. Maybe gunk from the radiator has it clogged again? I'm going to flush the whole system today.

The fans come on when the temperature gets to about 215° which is past the mid-point. I pulled out the relays and one had a little corrosion. I cleaned it out and put it back and then cleared the code. The code hasn't come back yet. But the fans still comes on at about 215°.
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Saturday, December 3rd, 2022 AT 6:06 AM
Tiny
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I have started draining the coolant. It appears to be almost empty. Not even 2 gallons have come out. Pretty sure the truck holds 3. So, I maybe had a lot of air considering the reservoir was always full.

The coolant is real clean too.
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Saturday, December 3rd, 2022 AT 10:26 AM
Tiny
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Drained and refilled. Sitting idle at 210 for about 20 minutes. Looks like it was air all along.

Thanks a bunch for the help.
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Saturday, December 3rd, 2022 AT 1:09 PM
Tiny
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  • MECHANIC
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Hi,

Thanks for the update. I'm glad it is back to normal. LOL Interestingly, this time of year is when I see this issue the most often. It's usually the result of a heater that isn't working after having the system flushed. It isn't uncommon but can be frustrating. LOL

Regardless, take care of yourself, and feel free to come back anytime in the future if you have questions. You are always welcome. And again, thanks for the update. It will likely help others in the future.

Joe
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Saturday, December 3rd, 2022 AT 8:41 PM

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