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Q: Van overheats, but only at idle - 2004 GMC Savanna 3500

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My van is having a problem with overheating when it idles. That is the only time that it overheats - just at idle. I have replaced the following parts: water pump, radiator cap, fan clutch, and the thermostat. One year ago, the head gasket was replaced and it performed in good condition after that replacement, until now. When it overheats, the coolant goes into the reservoir, but then when it is cool again the coolant does not go back into the radiator. I’m thinking this might mean a clogged radiator. But if that’s the case, then it wouldn’t happen at only idle. What is your professional assessment and how to fix it?

A: Hello. Assuming that you replaced the fan c...

Hello. Assuming that you replaced the fan clutch and the fan is actually working, I think you are on the right track as far as the radiator being clogged. When the vehicle is not moving, it does not have the same air flow that it does when the vehicle is moving. Due to the lack of air flow at idle, a clogged radiator would cause the vehicle to overheat.

When the vehicle is moving, the extra airflow passing the radiator might be just enough to prevent the vehicle from overheating even if the radiator is clogged. I would recommend getting the radiator tested for hot spots with a laser thermometer. If any hot spots are found, this would indicate that the radiator is clogged somewhere and the overheating would certainly be cased by this. If any hot spots are found, I would recommend having the radiator replaced by a qualified professional, such as one from YourMechanic. Once the radiator is replaced, the vehicle should no longer overheat.

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