Open the car hood and locate the thermostat on the top of the radiator lid. Pull the thermostat and start the car. Watch the temperature gauge carefully. If the water pump is working properly, the engine should take a long time to warm up (if it ever does). With the thermostat removed, the coolant should circulate continuously, making it harder for the engine to warm up. If you cannot tell if the car is heating up slow or not, move to Step 2.