I went back and make sure I read it correctly before I posted my response to you
Overheating ... "coolant overtemp"
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From: Highland Village TX
Overheating ... "coolant overtemp"
I have an '04 coupe with 50,000 miles on it. Was driving it the other night and car gave me a "coolant overtemp" warning within a few miles of starting the engine. I have changed the thermostat and water pump but the car will still go to max temp within a few minutes of starting the engine. After the enginge is warmed up, the radiator still feels cold to the touch and the heater inside the car does not blow warm air. Also, after the water pump change, the system did not draw very much coolant out of the reservoir. The car is definitely overheating. Not a gage problem. It seems as though i am not getting any flow of coolant at all. Please help. 
I need some ideas of what to look for or try next.
I need some ideas of what to look for or try next.
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radiator is clogged with sh**
fans not coming on
blown head gasket may result
fans not coming on
blown head gasket may result
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From: Highland Village TX
Yes, the problem was there before I did anything and yes, I would agree that there is air in the system now because the reservoir bottle did not drain down very much after I changed the water pump. Would seem like a lack of circulation in the system. The problem started very suddenly. The engine had been running at normal temps until it started overheating. The car only has 50,000 miles on it and the cooling system had never been worked on before and doesn't seem like the radiator would be bad with that many miles on it??? I am stumped. Would appreciate any ideas. Oh and yes, the fans are coming on as they should. One fan for the A/C and the other comes on at 235 degrees on the dot.
Last edited by PeterNLois; Oct 17, 2011 at 09:05 AM.
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Since it overheated before you made the change, I am not sure if air is your problem.But check this thread it has some good info.
http://forums.corvetteforum.com/c5-t...erheating.html
http://forums.corvetteforum.com/c5-t...erheating.html
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FIRST do a PRESSURE TEST on the system AND THE CAP. Clean the front of the Radiator and make sure the fans come on. Everyone want to blame air in the system-it's almost impossible to get air in the C5 system with the resevoir at the highest point in the system.
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From: Highland Village TX
I haven't done a pressure test but I do know that when the engine gets hot, there is pressure in the system. If I crack the reservoir cap when it is hot, it definitely has pressure behind it. Also, I checked the radiator and used an air hose to blow the gunk out. The car just gets soooo hot so quickly. It doesn't matter if it is sitting still or driving down the road with good air flow. Gets hot in just a few minutes from engine start.
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If the radiator is staying cold to the touch, you can eliminate the fans and the front vents being clogged with debris. The two things you mention should be the problem, the thermostat or the pump. I know it's new, but I'd be tempted to drop the thermo in hot water to insure it's opening. You know for sure you are not getting circulation or the radiator would heat up too. I hope you find it and post back what you find.
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crack the bleeder tube and its easy to bleed the system..takes 5 minutes
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If the radiator is staying cold to the touch, you can eliminate the fans and the front vents being clogged with debris. The two things you mention should be the problem, the thermostat or the pump. I know it's new, but I'd be tempted to drop the thermo in hot water to insure it's opening. You know for sure you are not getting circulation or the radiator would heat up too. I hope you find it and post back what you find.
but yes check the stat although failure is rare.
I too am anxious for the result
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there are 2 nuts to loosen...not remove...loosen 10mm
you can do it cold or warm/hot..cold takes a few minutes longer but is safer..just make sure the cap is off the overflow tank ..when you see the coolant running out you are good to go...just let it run for a few minutes
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From: Everett WA
Yes, the problem was there before I did anything and yes, I would agree that there is air in the system now because the reservoir bottle did not drain down very much after I changed the water pump. Would seem like a lack of circulation in the system. The problem started very suddenly. The engine had been running at normal temps until it started overheating. The car only has 50,000 miles on it and the cooling system had never been worked on before and doesn't seem like the radiator would be bad with that many miles on it??? I am stumped. Would appreciate any ideas. Oh and yes, the fans are coming on as they should. One fan for the A/C and the other comes on at 235 degrees on the dot.
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U either have a air bubble or even a warped head. Doesnt take much for the aluminum heads. I had the same problem with mine. Changed the thermostat twice, replaced the waterpump and the radiator. Took a bit longer but still over heated. So I took the heads off and sent them in to get shaved. As we speak motor is getting dropped back in the car. It was a reason to get a cam, headers, n upgraded clutch. 
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U either have a air bubble or even a warped head. Doesnt take much for the aluminum heads. I had the same problem with mine. Changed the thermostat twice, replaced the waterpump and the radiator. Took a bit longer but still over heated. So I took the heads off and sent them in to get shaved. As we speak motor is getting dropped back in the car. It was a reason to get a cam, headers, n upgraded clutch.
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From: Ringgold GA
Been there done that, cleaned air path, checked fans, changed water pump (twice), change thermo(checked in hot water), bleed system etc.
Mine would overheat and the hoses would be cool.
Check water flow through radiator. Mine was plugged. Replaced radiator and I am fine.
Easy to check - pull hoses off of water pump, rig up some type pipe fittings with connection for a garden hose and see if water will flow.
Dexcool crystalizes when it sets and is not flushed enough.
Note: Mine started only when I was sitting still and would cool off as I got moving again. Changed water pump and then I could not drive to the end of the street and it would get hot.
Mine would overheat and the hoses would be cool.
Check water flow through radiator. Mine was plugged. Replaced radiator and I am fine.
Easy to check - pull hoses off of water pump, rig up some type pipe fittings with connection for a garden hose and see if water will flow.
Dexcool crystalizes when it sets and is not flushed enough.
Note: Mine started only when I was sitting still and would cool off as I got moving again. Changed water pump and then I could not drive to the end of the street and it would get hot.
Last edited by Dan-G; Oct 17, 2011 at 08:27 PM.
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Great info in this thread and the link. Saved this for reference.