How to Know If a Thermostat Is Faulty on a Car

The thermostat sits between the radiator and the car’s engine. It blocks the flow of coolant to the radiator until the engine warms up before opening up. By doing this, it minimizes deposits and emissions, as well as wear and tear on the engine. Automotive parts can stop working over time, and the thermostat is no exception. However, there are ways to know if your car’s thermostat is faulty.

Things You'll Need

• Jump wires

Instructions

1. Take your car for a drive and notice whether the vents blow out warm air. If they do, your thermostat may be faulty.

2. Open the hood and make sure the cooling fan is running. If it’s not, the problem could lie in either the fan’s thermostat or the fan’s motor. Perform a test with a jump wire.

3. Detach the wiring harness from the fan. Take the jump wire and connect the ground (green) to the ground on the fan. Take the positive (red) wire and connect it the positive wire on the fan.

4. Use a second jump wire and connect one end to the negative post on the fan. Take the other end of the wire and attach it to any metal part on the car’s body. If the motor is working properly, the fan will turn on when you make this connection, and it would signify that you have a faulty thermostat. You’ll need to replace it. If the fan doesn’t turn on, the problem may be a faulty motor and not the thermostat.

Tips & Warnings

• If you determine that the thermostat isn't faulty, you consider having a diagnostic test performed to find the problem.

Resources

• Trust My Mechanic website
• Troubleshooters website for more tips