Jim Grant's Tech Tips
‘98 Chevy Blazer, Wild Temperature Gauge
Q: My ‘98 Chevy Blazer’s temperature gauge got pretty high, all of a sudden. Then the temperature gauge dropped all the way down. Then the service engine soon light came on and the engine ran funny but the temperature gauge went up again. Also, at stop lights or other stops the temperature would rise and go into the red easily. But, when the RPMs went up the temperature would drop again? What is wrong?
A: I can’t tell you what is wrong, but there are some checks you should perform. First, be sure the coolant is at the correct level. Don't just look at the level indicated on the coolant recovery tank. With the engine cool remove the radiator cap and check the level. A system problem can leave the coolant recovery tank level looking great, while the radiator is low. If the cooling system is at the correct level then you need to get into the vehicle’s computer to see what is happening. The coolant temperature sensor for the computer is also used for the temperature display on the dash. If the coolant temperature sensor is failing, it will cause rapid gauge fluctuation and cause the service engine soon light to be turned on. By monitoring the coolant temperature sensor movement and comparing it to the coolant temperature at the radiator you can determine if the sensor is providing a true reading of engine coolant temperature.