After checking the coolant level on the engine, the operation of the engine thermostat needs to be checked. One method to test and see if the thermostat is sticking open is to monitor coolant movement when the engine is cold. After removing the radiator cap, start the engine and watch for rapid coolant movement while the engine is in the warming-up stage. Seeing a lot of coolant movement during the warm-up stage is a sign that the thermostat is stuck open or is opening too soon. Either of these conditions will cause the heater to not get warm quickly enough.
Another way to determine if the engine thermostat is operating properly is to monitor engine operating temperature to see if the engine is able to reach normal operating temperature within a short time period. This process can be performed by watching the temperature gauge or by using a scan tool to monitor the engine temperature. Either method should produce reliable results.
The temperature of this outlet heater hose is
The heater core can be checked by testing the temperature of the heater hoses at the entry point and at the exit point. The temperature of this inlet heater hose is
A normally operating thermostat will allow the engine to reach the normal range of operation within 7 to 10 minutes of fast idle conditions. A thermostat that is stuck open will cause the warm-up time to take much longer than the normal time. A stuck-open thermostat will cause the operating temperature to run much cooler than normal when the vehicle is being driven on the highway too. Thermostats can stick closed, and when they do, the engine will quickly overheat.
