2004 base vette runs hot
Thread Starter
3rd Gear
Joined: Jul 2025
Posts: 3
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From: WI
2004 base vette runs hot
Hi all, I did a search already and read multiple threads on this, but didn't find exactly what I was looking for.
2004 Corvette base, auto trans. I replaced the radiator after the plastic one cracked. Cleaned everything, drove all Summer and stayed cool. Now that it's cooler, I noticed my car runs hotter. In the past, I would get up to 220 but it would then quickly cool, I assume fans kicked on. This morning driving to work on highway, It would go between 220 and 225, once around 225 I noticed fans must be engaging because it would go down to anywhere between 205-210...........but then creep up again. Then, closer to work, it got up to 235.........which I was alarmed by. Any help is appreciated.
2004 Corvette base, auto trans. I replaced the radiator after the plastic one cracked. Cleaned everything, drove all Summer and stayed cool. Now that it's cooler, I noticed my car runs hotter. In the past, I would get up to 220 but it would then quickly cool, I assume fans kicked on. This morning driving to work on highway, It would go between 220 and 225, once around 225 I noticed fans must be engaging because it would go down to anywhere between 205-210...........but then creep up again. Then, closer to work, it got up to 235.........which I was alarmed by. Any help is appreciated.
Tech Contributor
Joined: Jan 2007
Posts: 19,422
Likes: 1,146
From: Dyer, IN
Hi all, I did a search already and read multiple threads on this, but didn't find exactly what I was looking for.
2004 Corvette base, auto trans. I replaced the radiator after the plastic one cracked. Cleaned everything, drove all Summer and stayed cool. Now that it's cooler, I noticed my car runs hotter. In the past, I would get up to 220 but it would then quickly cool, I assume fans kicked on. This morning driving to work on highway, It would go between 220 and 225, once around 225 I noticed fans must be engaging because it would go down to anywhere between 205-210...........but then creep up again. Then, closer to work, it got up to 235.........which I was alarmed by. Any help is appreciated.
2004 Corvette base, auto trans. I replaced the radiator after the plastic one cracked. Cleaned everything, drove all Summer and stayed cool. Now that it's cooler, I noticed my car runs hotter. In the past, I would get up to 220 but it would then quickly cool, I assume fans kicked on. This morning driving to work on highway, It would go between 220 and 225, once around 225 I noticed fans must be engaging because it would go down to anywhere between 205-210...........but then creep up again. Then, closer to work, it got up to 235.........which I was alarmed by. Any help is appreciated.
- Is the coolant reservoir filled to the cold line before cold start?
-any evidence of leaks?
-how does it behave at parked/idle compared to driving?
-at what temperature do your fans kick on?
Thread Starter
3rd Gear
Joined: Jul 2025
Posts: 3
Likes: 0
From: WI
Thanks for the reply:
Coolant reservoir is filled to cold line before start.
No evidence of leaks at all.
Parked/idle it does not heat up too much. I mean it might rise 1 degree every couple minutes when idling.
I do not know the exact temp fans kick on, I haven't had the hood open when it's gotten that hot, that's something I can check tonight. I am just guessing around 225 as that is when I see the temps dropping most of the time.
Coolant reservoir is filled to cold line before start.
No evidence of leaks at all.
Parked/idle it does not heat up too much. I mean it might rise 1 degree every couple minutes when idling.
I do not know the exact temp fans kick on, I haven't had the hood open when it's gotten that hot, that's something I can check tonight. I am just guessing around 225 as that is when I see the temps dropping most of the time.
Melting Slicks
Joined: Sep 2021
Posts: 2,555
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Failed thermostat? New debris blocking the radiator? Air dam fell off or wore away?
Weird that it worked all summer.
You would think it would heat up at idle too if the thermostat failed or radiator was blocked.
Weird that it worked all summer.
You would think it would heat up at idle too if the thermostat failed or radiator was blocked.
Melting Slicks
Joined: Sep 2008
Posts: 3,135
Likes: 802
From: Espanola New Mexico
The fans turn off at 35 mph, if your seeing higher temperatures at highway speeds then most likely the thermostat may be the problem, or problem with the air dam, or radiator fins maybe clogged with road debris.
Advanced
Joined: Jul 2023
Posts: 92
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From: SW CO
Running hot only at speed can be caused by a clogged radiator [likely not in your case], restricted air flow, and a thermostat that does not open fully.
How many miles showing?
Did you replace the thermostat with the radiator? If so, is the thermostat an OE part?
How many miles showing?
Did you replace the thermostat with the radiator? If so, is the thermostat an OE part?
Tech Contributor
Joined: Jan 2007
Posts: 19,422
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From: Dyer, IN
Below 35 mph.....Provided the indicated temperature is correct, you can force the low speed cooling fans to come at an indicated temperature above 185 F with the A/C on.
Thread Starter
3rd Gear
Joined: Jul 2025
Posts: 3
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From: WI
Definitely not a clogged radiator, I will check the air dam as I recently had it at a shop doing the torque tube and maybe it got jacked up on the lift? I'll look tonight.
I did not do the thermostat when I did the radiator, but I could do that. I was exploring a lower temp thermostat and also having the tuning change to turn fans on at lower temp.
Since it's fairly easy, I'll start with a new thermostat. FYI, 74K miles.
I'll get more info. at home with the hood open to check fans and use an IR thermometer to get more accurate data. Thank you all for the help, I'll let you know what I can find out.
I did not do the thermostat when I did the radiator, but I could do that. I was exploring a lower temp thermostat and also having the tuning change to turn fans on at lower temp.
Since it's fairly easy, I'll start with a new thermostat. FYI, 74K miles.
I'll get more info. at home with the hood open to check fans and use an IR thermometer to get more accurate data. Thank you all for the help, I'll let you know what I can find out.
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Tech Contributor
Joined: Jan 2007
Posts: 19,422
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From: Dyer, IN
Advanced
Joined: Jul 2023
Posts: 92
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From: SW CO
When you are checking the undercar aero, look for anything obstructing air flow into the radiator/condenser area.
When you changed the radiator, did you refill with GM Dexcool OAT coolant or equivalent? Dexcool is a fine coolant but does not like to be mixed with other types.
Melting Slicks
Joined: Sep 2021
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Advanced
Joined: Jul 2023
Posts: 92
Likes: 22
From: SW CO
I don't know if the "universal" [HOAT] coolants of today will react negatively when mixed with Dexcool. You will find many who report mixing coolant types with no apparent negative effects. I never argue with others' reported success.
Initially, Dexcool/GM took a bad rap for this, but in my opinion it is the result of an uninformed shop or individual.