QuestionHow do I fix an overheating problem?
The temperature gauge is half way between C and H while driving, but the anti-freeze in the recovery bottle boils once the car is turned off. Have had the problem repaired twice over the last 2 years, the fan relay switch was replaced each time.
AnswerSteve, my fear is that you have a head gasket problem that is allowing exhaust gases into the coolant. Without an air compressor, however, there will be no effective way for you to test for this. Since we know the problem occurs after being driven, the way to test for this would be as follows:
1. Drive vehicle an appropriate amount of time.
2. Remove spark plugs.
3. Using extreme caution, remove radiator cap.
4. One by one, turn the engine so that the valves on each cylinder are shut. While shut, apply compressed air to the cylinder and check for bubbles in the radiator. Such bubbles imply that the head gasket is leaking (and that most likely the cylinder head is warped beyond repair).
Your problem could also be caused by very low coolant. If there's an air pocket where the coolant temperature sender is located, the gauge will not read the proper temperature.
I'm not entirely sure exactly what was done prior, as your car has no "fan relay switch." The fan works as follows:
1. The engine control module (ECM) receives information from the coolant temperature sensor.
2. Based on information from the coolant temperature sensor, the ECM grounds one or both of the fan relays.
3. The fan relays then close, supplying power to the fans.
When diagnosing a cooling system problem, it's important to determine which parts of the system are working properly. Since you've a boiling condition even though the gauge reads halfway, it's important to determine whether the gauge is providing the proper reading. I'd typically do this by using a scan tool and comparing the coolant temperature reading on the tool to the gauge position. Presuming you don't have such a tool, you might remove the radiator cap, start the engine, and monitor coolant temperature in relation to the gauge position.
Once you know the gauge is operating properly, you should be able to perform a cooling system audit as follows:
1. Start the car and turn on the A/C. Both fans should run. If not, you have an electrical problem in one of the fan circuits (relay, wiring, fan motor, etc.)
2. Remove the radiator cap and check the coolant level. (Actually, I presume this was already done checking the gauge). If low, check for leaks. Unless they're so large that the system cannot be kept full, you can temporarily add coolant to continue testing the rest of the system. Just keep in mind that they'll need to be repaired.
3. Start the engine with the cap still off.
4. As the gauge reaches the halfway point, the coolant should begin to flow. Typically, you can see this in the radiator; this is why I've suggested keeping the cap off. If you cannot see the flow, you can feel the radiator hoses. If one is hot and one is cold, you do not yet have coolant flow. If the coolant begins to boil prior to the coolant flowing, you should check to see if your thermostat is stuck shut.
5. After the coolant begins to flow, the radiator fans should eventually come on. If the coolant begins to boil prior to the fans operating, you'll need to investigate why the ECM isn't turning on the fans. And this is where I'd be likely to begin suspecting a head gasket issue. If the exhaust is pumped into the cooling system, it can create a pocket around the coolant temperature sensor, preventing it from reading the proper coolant temperature.
