Comments on: How to Tell if Your Car's Thermostat Is Stuck Closed

on 6/16/2009 Step 6 makes no sense. If the thermostat is NOT stuck closed, hot water will flow to the top of the radiator. The purpose of the radiator is to cool the water, so the bottom hose will be cool.

on 1/2/2008 A thermostat sticks open and closed randomly for several reasons. headgasket sucking air, water pump sucking air, frigid cold can fail even a good thermostat into bizarre actions. This after acknowledging the system is not using coolant. Also a reservoir will fill up with cold fluid if thermostat is stuck closed in the cold. An engine can do many different things and make a thermostat problem elusive. You could also pack up and move towards 70 degrees where none of this will be of concern for decades at a time and hope the crazy north gets manly parts that function after 100+ years of the internal combustion engine resides in paradise with the other engineers of no concern.

on 11/22/2005 If you're driving down the freeway and your car is about to overheat because you have a stuck thermostat, turn off the air conditioner, and put the heat on full blast. Engine coolant will run through the heater core and be cooled by the heater blower. This should get your coolant temperature down a little bit to keep you going. Yes, it will be very hot, but open the windows and think of how you'll no longer be stuck on the highway.

on 2/12/2007 This should be done only as a last resort and should confirm any doubt after following any of the previous tips.

Remove the thermostat and place it in a coffee mug of boiling water (roughly 180-200 degrees). If the thermostat fails to open, it is faulty. If it does open, your problem lies elsewhere.

on 6/11/2007 With the engine cold, remove the radiator cap and warm the engine up. Normally, at startup, the coolant should be still. But as the engine warms up to normal operating temperature, the thermostat should open, and the coolant will stir with the water pump. The churning action of the water pump would be more apparent if you rev the engine up. Based on this normal thermostat operating scenario, you should be able to determine if your thermostat is stuck open or closed.

on 11/22/2005 If the temperature gauge rises only slightly, the thermostat is stuck open. The engine will never properly warm up. In a cold climate, the cabin will never get warm and mileage will drop drastically.

on 1/4/2007 Symptoms of weak, open thermostat: engine temperature does not get up to normal; heater puts out only warm or cool air; engine may not perform up to normal standards; hoses may be cooler than normal (touch carefully).

on 11/22/2005 If the upper radiator hose is hot at the engine end and cool at the radiator end, coolant is not circulating. The upper hose is normally cooler than the lower hose due to cooling via the radiator.

on 11/22/2005 You will get almost identical symptoms to a sticking thermostat if you fit a normal thermostat to a car that requires a dual-acting thermostat (eg., some Corvettes). A dual-acting thermostat has a spring-loaded valve that closes the bypass circuit.

on 5/22/2007 When there is a continuous rise in temp in temp indicator, then watch for leakage in the radiator, heater core & hoses, through dummies fixed at the bottom of engine block if it is casted. If there is no leakage in these then thermostat could be faulty.

on 11/22/2005 With engine cold, remove radiator cap. Start car and watch the fluid level at radiator opening. When engine warms up the thermostat opens and the water level goes down because it's being released through the thermostat to circulate and cool the motor.