Test a Thermostat
The thermostat in your car controls the flow of coolant between the engine and radiator, and you can actuallytest a thermostatwithout removing it from the engine using a simple procedure. If you suspect your engine is overheating or overcooling because of a bad thermostat, you can do one of two simple tests. Just choose the correct test according to the type of radiator you have installed in your car.
If the radiator has no neck
You can easily tell your radiator has no neck because you won't find the common radiator cap. If this is your case, follow this procedure to test your thermostat. To find the thermostat, follow the upperradiator hosetowards the engine. On the engine side, the upper radiator hose connects to a metal or plastic housing. Underneath this housing is where your thermostat lives.
Testing the thermostat
First, make sure the engine is completely cool or that your vehicle hasn't been driven in the past two hours. Using a simple cooking thermometer, take a temperature reading of the engine close to thethermostat housing. We'll call this spot number 1. Next, take a temperature reading of the upper radiator hose near the thermostat housing. We'll call this spot number 2. Write down these two temperatures using a piece of paper. Now, start the engine and let it idle for about 10 or 15 minutes.
Warning: If you are troubleshooting the thermostat because the engine overheats, keep an eye on the temperature gauge on the dashboard. If the needle on the gauge gets too close to the red line before reaching the ten or fifteen minutes, turn off the engine immediately. Then, go ahead with the rest of this test.
After 10 or 15 minutes of engine operation, turn off the engine and take a temperature reading of spot number 1 and 2. Now, compare the two sets of readings. If the temperature in each spot is between 80 and 210 degrees Fahrenheit (80 and 100 degrees Celsius), your thermostat is working properly. This is a typical engine operating temperature. However, if you noticed that neither spot 1 nor spot 2 reached normal operating temperature, your thermostat is stuck in the open position and needs to be replaced. On the other hand, if spot 1 reached normal operating temperature but spot number 2 didn't, your thermostat is stuck in the closed position and you need to replace it.
If the radiator has a neck
You can tell your radiator has a neck because it has the radiator cap on it. Before you can proceed with this test, though, make sure the engine is cool or hasn't been driven in the previous two hours. Now, follow the upper radiator hose towards the engine. This hose connects to a plastic or metal housing. Underneath this housing is your thermostat.
Testing the thermostat
Remove the radiator cap, crank up the engine and let it idle for about ten to fifteen minutes so that it reaches normal operating temperature. As soon as your engine starts, take a look at the coolant through the radiator neck. The fluid shouldn't move or flow. If you see the coolant flowing, your thermostat is stuck in the open position and needs to be replaced. Otherwise, continue with this test.
Warning: If you have an engine-overheating problem, keep an eye on the temperature gauge on the dashboard. If the needle on the gauge gets too close to the red line before reaching the 10 or 15 minutes, make sure the coolant is flowing at this point. Then, shut off the engine immediately. If you saw the coolant flowing, before shutting off the engine, you know the thermostat is working, and your overheating problem lays somewhere else. However, if the coolant wasn't flowing, your thermostat is stuck in the closed position, causing your engine to overheat. Replace the thermostat.You can reach the same conclusion when checking for coolant flow-as described in the previous paragraph-once your engine has reached the ten or fifteen minutes of operation. If the coolant was flowing before shutting off the engine, the thermostat is working properly. If the coolant wasn't flowing, though, the thermostat is stuck closed and needs to be replaced.
Do you suspect your thermostat has failed? Troubleshoot it without removing it from the vehicle. A thermostat stuck in the closed position will cause your engine to overheat and will self-destruct in minutes if the engine isn't turned off on time. A thermostat stuck in the open position will cause your engine to overcool and lead to poor engine performance and greater fuel consumption. You can do this test in a few minutes. It doesn't require special tools and you can save your engine from major disaster.
