My 2004 Buick Lesabre has a cold radiator and the reserve tank is cold also. The top and bottom hose are warm. There is good heat inside. and the temperature gauge reads normal. I don't see any leaks and the water pump was replaced two years ago. To my knowledge the radiator should be warm. Is that correct? Is there a problem? The car has good power acceleration. the outdoor temperature is about 33 degrees F.

Thanks for your help,Jim

I revved up to 2000 rpms for 3 minutes and turned the heat off and the radiator got warm but the reserve tank stayed cold.


  • What problem are you having? This sounds like normal operation. The thermostat is not open yet because at idle the heater core is drawing away enough heat from the engine. Shut off the heat and run the engine at 2000rpm and the thermostat will open.
    – vini_i
    Commented Nov 10, 2017 at 18:11
  • Thanks for the info vini . I always thought that the radiator was supposed to be hot. I will try what you said and let you know what happenes.
    – JIM
    Commented Nov 10, 2017 at 18:17
  • The reserve tank is there only to deal with expanding coolant. It may not get hot.
    – vini_i
    Commented Nov 10, 2017 at 20:35
  • 1
    Also, make sure you're actually seeing that the radiator is cool, and not the AC condenser coil. They're usually stacked, so it's not hard to make the mistake.
    – JPhi1618
    Commented Nov 10, 2017 at 21:46
  • @vini_i - Post it as an answer ... it's the way I see it as well. Sound advice. Commented Nov 11, 2017 at 1:59

1 Answer 1


The cooling system is meant to control the temperature of the engine. The key word there is "control". An engine wants to run around 195F. This varies depending on engine and manufacturer.

The whole thing with "control" is that if the temperature is too high the engine will give heat away. If the temperature is too low, this is the key part, the engine will hold the heat in.

The engine does this in a couple of different ways. The first is the thermostat. The thermostat is a temperature sensitive valve. When the temperature preset of the thermostat is met it opens and allows coolant flow into the radiator. If the temperature drops the thermostat will close again. The next is the radiator. When hot coolant enters the radiator, the radiator gives the heat off to the air. If the radiator alone can not shed the heat the radiator fan kicks in to help.

The heater core in this setup is an outsider. The heater core steals heat from the engine and the engine can't control this. This can disrupt the process, kind of.

When the engine is idling it does not make all that much heat when compared to under load. Couple that with freezing temperature outside and the heat on full blast and the engine can't get up to temperature. This intern keeps the thermostat closed does not allow hot coolant to enter the radiator. This is normal operation. The engine is trying to keep in the heat until it can reach the desired temperature.

Shut off the heat. Run the engine at 2000rpm. This simulates more of a load condition. This will cause the engine temperature to rise, the thermostat to open and the radiator to get hot.

The reserve tank comes in one of two types; overflow or degass. The overflow tank just catches extra coolant when there is extra and when the cooling system gets in a vacuum it will suck some out of the overflow. The degass tank is part of the cooling system and gives the coolant a place to expand. This keeps all the coolant in the cooling system (meaning no overflow). If the degass tank overflows then something went wrong. Neither style of tank is required to get hot. They sometimes do. They both should be filled to withing the required lines on the side of the tank.

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