c5 Car overheating
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Joined: Jul 2009
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From: Kentucky
c5 Car overheating
Okay, my 99 c5 has been getting a bit warm here lately (and yes it has been very hot here in Western Ky). Here is the deal, my car with the A/C off will reach temps of 235 degrees while sitting still in the driveway or stoplights. The radiator fans will never kick on by themselves at this temp. I have checked all the relays and fuses under the hood, and they all seem to be working as they should. Now when I turn the A/C on the right side fan kicks on low speed, then after a little while longer the high speed fan mode kick on, once it drops 2 degrees it will kick back off back to low speed. once I shut the A/C off, the fans kick off and the temp spikes up. On really hot days such as the 100 degrees plus it has been for the last month, with the A/C on it still runs 230+ degrees. Also the car does not run hot while being driven down the road, so there isn't ay trash between the radiator and condensor (I did check) and the thermostat is definitely opened. The coolant tank is completely full when I removed the cap today, so it isn't low on coolant. Any ideas? Its about to drive me nuts having to turn on the heater to get the temperature to drop. Any insight on this would be greatly appreciated.
Thanks
Thanks
Team Owner
Joined: May 2003
Posts: 23,480
Likes: 9
From: East Meadow NY
St. Jude Donor '12
When you said you checked for blockages around the radiator, did you just look or did you clean it out? The debris can build up over time and it won't necessarily be a big object blocking it.
I am nt sure why the low speed fan isn't on for you.
I am nt sure why the low speed fan isn't on for you.
Last edited by chaase; Jul 28, 2012 at 11:03 PM.
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Joined: Jul 2009
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From: Kentucky
I only looked for blockages, didn't actually take anything apart for through cleaning. Although it did look realtively clean under there. I may just try purchasing a new low speed fan relay and giving that a shot, I'm not real sure what else could be the cause since the fan motor itself works with the A/C on.
Racer
Joined: Mar 2009
Posts: 394
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From: Everywhere US
I still have a couple of these made up ..... shoot me a PM if you'd like me to send you one ......
makes cleaning between the radiator and condenser easy .......
makes cleaning between the radiator and condenser easy .......
Last edited by LastC3AZ; Jul 29, 2012 at 11:12 AM.
Race Director
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From: Phoenix area, AZ
Team Owner
Joined: Jul 2006
Posts: 22,150
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From: Kannapolis NC
I suggest that you do in fact have relay problems related to the fans and or a bad fan.
Normal operation of the C5 cooling system is that BOTH fans kick on at 225 degrees in low speed operation and if the coolant goes down to 219, then the fans kick off. If the temp rises to 235 degrees then BOTH fans go to high speed operation. If the coolant reaches 226 degrees the fans revert to low speed operation. If the vehicle reaches 35mph then the PCM commands the fans OFF irrespective of engine temp.
It's possible that a previous owner has had the turn on and off temps adjusted but they usually pick lower temps than factory.
Here is a wiring diagram for the fans:
I am assuming you know how to read the wiring diagram.
Normal operation of the C5 cooling system is that BOTH fans kick on at 225 degrees in low speed operation and if the coolant goes down to 219, then the fans kick off. If the temp rises to 235 degrees then BOTH fans go to high speed operation. If the coolant reaches 226 degrees the fans revert to low speed operation. If the vehicle reaches 35mph then the PCM commands the fans OFF irrespective of engine temp.
It's possible that a previous owner has had the turn on and off temps adjusted but they usually pick lower temps than factory.
Here is a wiring diagram for the fans:
I am assuming you know how to read the wiring diagram.
If your temp is reaching 235 and neither fan is coming on, cleaning your radiator is not going to make it happen. Both fans should be running at 226 and with the a/c on.
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Joined: Jul 2009
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From: Kentucky
Thanks for all the helpful suggestions, I replaced the relays and the fans seem to be kicking in and out as it should with and without the A/C on. I went ahead and replaced all the cooling fan relays while changing out the oil pressure swtch yesterday. The car seems Thanks again guys- David
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Melting Slicks
Joined: Nov 2009
Posts: 2,922
Likes: 219
From: West Branch, MI
Here's another great option as well. Here in OKC we're seeing temps in the 105º-110º range right now. Not unusual for us, but that doesn't come close to places like Phoenix or Las Vegas. I knew we had hot summers here, so I ordered the Cool It from SacCityCorvette. A very cool (pardon the pun) product that installs in 5 minutes and you can control the right side fan with a remote control. Really nice for parades, sitting in traffic jams, etc. Keeps the fan on high until you turn it off, and auto shuts off when you turn off the key. Nice product for the $$. Glad you got yours sorted out. 
Here's a link to their site and products:
http://www.saccitycorvette.com/COOLITv2.html
Here's a link to their site and products:
http://www.saccitycorvette.com/COOLITv2.html
Tech Contributor
Joined: Jan 2007
Posts: 19,388
Likes: 1,134
From: Dyer, IN
Okay, my 99 c5 has been getting a bit warm here lately (and yes it has been very hot here in Western Ky). Here is the deal, my car with the A/C off will reach temps of 235 degrees while sitting still in the driveway or stoplights. The radiator fans will never kick on by themselves at this temp. I have checked all the relays and fuses under the hood, and they all seem to be working as they should. Now when I turn the A/C on the right side fan kicks on low speed, then after a little while longer the high speed fan mode kick on, once it drops 2 degrees it will kick back off back to low speed. once I shut the A/C off, the fans kick off and the temp spikes up. On really hot days such as the 100 degrees plus it has been for the last month, with the A/C on it still runs 230+ degrees. Also the car does not run hot while being driven down the road, so there isn't ay trash between the radiator and condensor (I did check) and the thermostat is definitely opened. The coolant tank is completely full when I removed the cap today, so it isn't low on coolant. Any ideas? Its about to drive me nuts having to turn on the heater to get the temperature to drop. Any insight on this would be greatly appreciated.
Thanks
Thanks
Team Owner
Joined: May 2003
Posts: 23,480
Likes: 9
From: East Meadow NY
St. Jude Donor '12
Thanks for all the helpful suggestions, I replaced the relays and the fans seem to be kicking in and out as it should with and without the A/C on. I went ahead and replaced all the cooling fan relays while changing out the oil pressure swtch yesterday. The car seems Thanks again guys- David
