CHEVY OVERHEATING

2002 Chevrolet Impala

Tiny

grey-hair

July, 4, 2010 AT 11:15 AM

Engine Cooling problem
2002 Chevy Impala 6 cyl Front Wheel Drive Automatic 170000 miles

1 1/2 years ago had the head gaskets replaced, they were the cause of overheating. Now it's overheating again. The water pump and thermostat have been replaced, the lower radiator deflector is missing. When I drive the car it will go to 210-220 I will then park and let it idle temp does not come down until I turn on the A/C the fans kick on and the temp comes down to normal. When the car was cold I drained some coolant out so I could see the first row of the radiator. With the cap removed I started the car when it got to normal temp I could see good flow out of the top row of the radiator. If I start the car and let it idle for at least a half hour it will run at normal temp never getting hot

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4 Answers

Tiny

caradiodoc

July, 4, 2010 AT 2:45 PM

Hi grey-hair. Welcome to the forum. Sounds like a problem with the coolant temperature sensor if the radiator fan doesn't turn on without having to turn the AC on. To verify the lack of a fan is causing the overheating, next time it runs too hot, turn the heater on maximum hot and fan on high. That will act like a small radiator.

Also check for multiple fan relays in the fuse box under the hood. Some cars have a low and a high speed relay and some have one for just the radiator fan and another that runs both the radiator and the AC fans. A fast test for relays is to switch two indentical ones around to see if a different circuit stops working.

Some vehicles, minivans in particular, use an electronic fan relay module with multiple inputs. That would also be a likely suspect.

Caradiodoc

Tiny

grey-hair

July, 4, 2010 AT 3:58 PM

I just drove it 50 miles on the highway at first it was ok then comming back it ran at 210. Shouldn't ram air at 80 mph be sufficent airflow to keep it cool? Just now I ck'd the temp sensor and it has 5 vdc to it and through the sensor I see an open circut, I only had one fault and that was po420 I replaced the downstream o2 sensor and cleared the fault. If the temp sensor is bad shouldn't that show as a fault?

Tiny

grey-hair

July, 4, 2010 AT 5:54 PM

Sorry, the temp sensor is good I had the meter set wrong. It was 1400 ohms at around 100 degrees.

Tiny

caradiodoc

July, 19, 2010 AT 5:23 PM

Sorry I missed your replies. I was out of town at the nation's second largest old car show swap meet.

1400 ohms is acceptable for the coolant temperature sensor but the 5.0 volts is not unless you measured that while it was unplugged. If you back probe the connector while it's plugged in, you should find between 0.5 and 4.5 volts. The higher the temperature, the lower the voltage. By the way, are you on a two-wire sensor? If it only has one wire, you're looking at the sensor for the dash gauge.

The fan should not be needed at highway speeds. If turning on the heater fan helps, check the radiator for corroded and crumbling cooling fins.

Caradiodoc.

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