# 04 Tahoe Overheating, Changed Thermostat, still overheating!



## Mobetta72

2004, Chevy Tahoe, 5.3, 2WD
My Tahoe started overheating a few days ago with antifreeze/water burping out of the reservoir. I thought it was the thermostat so I changed it, but that didn’t help the problem. When idling with the radiator cap off, the antifreeze/water starts burping out the reservoir. What’s the problem? Please help! Thanks


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## shakey gizzard

Check the fan clutch first, then water pump and radiator!


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## Slug-Gunner

First, make sure that your electric fan for when the A/C system is ON is working properly.  This should come on any time the A/C system is ON when the ambient air temps are above a certain point - usually above 75-80 degrees since the A/C system places additional 'loads' on the engine cooling system.  If not, check the fan relays that control this.

If your Tahoe uses the "DexCool" (orange) GM coolant, that may be the 'overheating' problem.  If this stuff gets exposed to 'air', it can cause it to coagulate into a 'gelatin' in your engine, heater core, and radiator..... thus clogging up the flow of coolant thruout the cooling system. 

Have you ever had to add 'water' to your cooling system when it was low?  If so, did you use 'tap' water or only 'distilled' water?  Only 'distilled' water should be used to 'top-off' either cooling systems or batteries.


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## Lukikus2

It still could be the thermostat. I've got some bad one's before. Every time I buy a new one now I will put it on the stove in a pot of water and bring it to a boil and make sure it opens before boiling point. Got three bad one's in a row one day is the reason I do this now.


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## mdgmc84

Lukikus2 said:


> It still could be the thermostat. I've got some bad one's before. Every time I buy a new one now I will put it on the stove in a pot of water and bring it to a boil and make sure it opens before boiling point. Got three bad one's in a row one day is the reason I do this now.



Easiest way to check one. Its what i do.


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## M80

I've seen the waterpump blades wear on these vehicle's.  I'd change the waterpump.  They are not bad at all.  Hardest thing is nocking fan clutch loose and it even isn't that bad.  

Worst case  is a Blown Head Gasket.

How long does it take before it starts bubbling in radiator once you start vehicle.


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## 1gr8bldr

Are you not seeing just a little leakage from under the vehicle. Mine did this. Had a slight leakage at the water pump. It got a little low. Got air in the system and was burping like you described. I had to watch my gauges. Sometimes I would pull over and add a little coolant. Kept it in the back of the truck until I had time to put it in the shop. I was working out of town at the time so this went on traveling back and fort each day for 4 months. New water pump took care of the problem


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## deadend

Tahoe water pump is a breeze to replace.


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## Mobetta72

Thanks Guys, took it to a shop to get it checked out and NOTHING! Truck is running at normal temperature now. Shop said that it probably had a air pocket in the system after we put in the new thermostat. Drove the truck all day yesterday and temperature never rose above 210. I'm still at a loss for words!!

Thanks again for your help!!


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## Maloghost502M

Slug-Gunner said:


> First, make sure that your electric fan for when the A/C system is ON is working properly.  This should come on any time the A/C system is ON when the ambient air temps are above a certain point - usually above 75-80 degrees since the A/C system places additional 'loads' on the engine cooling system.  If not, check the fan relays that control this.
> 
> If your Tahoe uses the "DexCool" (orange) GM coolant, that may be the 'overheating' problem.  If this stuff gets exposed to 'air', it can cause it to coagulate into a 'gelatin' in your engine, heater core, and radiator..... thus clogging up the flow of coolant thruout the cooling system.
> 
> Have you ever had to add 'water' to your cooling system when it was low?  If so, did you use 'tap' water or only 'distilled' water?  Only 'distilled' water should be used to 'top-off' either cooling systems or batteries.


Mine is doing the same, I have changed the waterpump, thermostat and housing, hoses, to include the belts as well. What now???


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## Lukikus2

Mobetta72 said:


> Thanks Guys, took it to a shop to get it checked out and NOTHING! Truck is running at normal temperature now. Shop said that it probably had a air pocket in the system after we put in the new thermostat. Drove the truck all day yesterday and temperature never rose above 210. I'm still at a loss for words!!
> 
> Thanks again for your help!!



These newer trucks need to be burped. Just ran into one last week. A air pocket does form.


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## Maloghost502M

Lukikus2 said:


> These newer trucks need to be burped. Just ran into one last week. A air pocket does form.


I ran the tahoe heating system and all I was getting was cold air...90 on the front dash, 90 for the back. I will try running it again to see if the vehicle will burp?!?!?!


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## mguthrie

Maloghost502M said:


> I ran the tahoe heating system and all I was getting was cold air...90 on the front dash, 90 for the back. I will try running it again to see if the vehicle will burp?!?!?!


I replaced the thermostat in my Tahoe and had to add coolant through the top radiator hose to get the air bubble out. I’m guessing the thermostat wouldn’t open because of the air


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## Robust Redhorse

My 2003 did the same thing, but only when towing (a light trailer - 3,000 lbs).


It finally came down to a radiator replacement.  


I ended up selling it, even though it had been a great car for a looooong time .  It was getting close to 300K and I didn't want to spend the $.


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## Ajohnson0587

I have worked for GM dealerships since 2007 so have a lot of experience, a lot of times air will get trapped in the heater core or the engine block, this can be burped by leaving the cap off the reservoir after filling the cooling system and letter the engine idle. Sometimes on the more stubborn vehicles we'd remove the coolant temp sensor in the cylinder head and this would force out the air pocket. There could be other issues like a blown head gasket, but its not common on these trucks. Best thing to do if you can't get it to burp is take it to a qualified mechanic, don't risk further damage. I have a tool that will put a vacuum on the system to remove all the air, I just switch the valve and it begins to draw in the coolant/antifreeze, this guarantees no air will get trapped and cause over heating.


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