I have been frustrated by the number of cases of overheating in subaru legacy and outbacks that relate to thermostat malfunction. In a lot of cases the thermostat will test ok and there does not seem to be trapped air or any faulty components . I had the same issues and found an answer. The subaru thermostat opens by reading the temperature of the coolant in the return heater line to the water pump. Have you ever wondered why the return is right there? Once this has been digested, thermostat problems can often be traced to the heater core or heater hose. A loss of pressure (blockage )or low temp will stop the thermostat opening normally even though it tests OK . Please check my information(google subaru engine conversions) or (getting trapped air out of subaru) and there are plenty of accounts and warnings of how the heater circuit can cause overheating. Hope this can help, and email me if required. Michael.
- posted
16 years ago