Troubleshooting Cooling System Problems
Diagnostic guide covering overheating, temperature fluctuation, fans running after shutdown, and coolant loss on the 944.
1. Car Runs Hot / Temperature Fluctuates
a. If the car runs hot and the radiator is cool, the thermostat sticking closed is a possible cause. b. The coolant system may not be properly vented. c. There may be a blockage in the hoses or radiator. d. The cooling fans may not be operating properly. This can be caused by the fan relays, fuses, or the thermofan switch. One fan is for normal temperature-controlled operation; the other normally runs when the A/C is on. e. An incorrect water/antifreeze ratio can cause overheating. For most climates a 50/50 mixture is appropriate. f. The head gasket may be leaking. g. The water pump may be bad. Rebuilt water pumps have been known to have the pulley slip on the shaft; others have had the impeller separate from the shaft. h. The temperature sensor or gauge may be faulty. i. The radiator cap may be faulty. A coolant pressure tester is needed to test the cap; many major auto parts stores can perform this test.
2. Cooling Fans Keep Running After the Car Is Shut Down and Drain the Battery
a. Most likely cause is the thermofan switch. Replace it using the COOL-05, Thermofan Switch Replacement procedure. b. This may also be caused by a faulty fan relay.
3. Coolant Loss
a. The head gasket may be leaking, allowing coolant into the cylinders. White smoke from the exhaust is a common indicator. Perform a compression check. b. A cylinder wall may be cracked, allowing coolant into the cylinder. White smoke from the exhaust is a common indicator. Perform a compression check. c. The oil cooler seal may be leaking, allowing coolant and oil to mix. Look for a white, frothy residue in the coolant tank or on the radiator cap (this applies only to early 944s with an oil cooler integral to the block). d. Check for an external head gasket leak. Small leaks may evaporate before coolant reaches the ground, especially if the leak only occurs when the system is pressurised. e. Check for hose leaks, a leaking radiator core, a leaking heater core (a strong antifreeze smell in the passenger compartment is the indicator), a leaking system vent, and a leaking radiator drain plug. f. Check for a leaking water pump seal. g. Check at the rear of the engine near the firewall for a leaking heater control valve or leaking hoses to the control valve. h. Check for a faulty radiator cap (pressure-test the cap).