QuestionHello,
My temperature gauge fluctuates from hot to the middle mark. Sometimes it will stay at hot but my car will never overheat. When I turn on my heat it blows out cold air until I get on the freeway (where I'm accelerating continuously)then it will blow out hot air. If I come to a red light or put my car in park it will begin to blowout cool air. While the air goes from cold to hot my temperature gauge fluctuates. Do you any idea what would cause this?
AnswerHi Jamine,
Temp gauge fluctuation is fairly normal and reflects the function of the thermostat. The swing sounds a but too extreme though so I have some other theories.
I wonder whether you might have a less than full coolant system. When you check the level in the overflow when the engine is cold, is there coolant up to the minimum mark on the side of the bottle? If it isn't you can have air in the rest of the system to the extent where it is low on coolant and that can cause inefficient movement of the coolant to the heater core. So check that level when cold.
Another thing to check would be to look behind the engine and notice a couple of rubber hoses that pass side by side thru the firewall and into the cabin, about midline of the vehicle. Those are the heater core coolant in and out hoses. When the engine temp is at least half scale on the gauge, stop the car, open the hood and touch those hoses and compare the temperature of them. If they are both equally hot, that is a sign of good flow through the heater circuit. If one is noticeable cooler than the other that would be a sign of restricted flow through that circuit, most likely the heater core which might be partially blocked with corrosion, etc. What you would want to do then is drain off some of the coolant into a pan for reuse via the radiator draincock, then disconnect the two hoses where they attach to the engine, then flush water into the colder hose by means of a garden hose attached to the domestic water supply so as to flush out and debris at the end of the other removed hose. This may improve the flow through. Reattach the hoses and refill the system and then see if the heat is better.
Finally, if the hoses seem to be equally hot there is the possibility that the door in the HVAX box under the dash that is responsible for mixing the heated and cooled air that normally is present together in the outflow is shifting around uncontrolably due to an electical issue with the door position actuator motor. This is not highly likely but could help explain.
What is the history of this sort of problem? Anything unusual happen when it started to behave this way?
Please let me know what you learn or want to share.
Roland
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