If My Car Thermostat Starts to Fail What Should I Do?

The car's thermostat is a straightforward and easy device. However, if it fails, it could cause severe issues. Find out more about identifying the indicators of a malfunctioning thermostat for your vehicle.

Symptoms of a Failing Car Thermostat

Fortunately, a thermostat issue is among the numerous car issues you can identify and fix yourself. Here are some signs that your car's thermostat is not working:

• The temperature gauge shows high, and the engine starts to overheat.
• The temperature changes in an erratic manner.
• The coolant in the vehicle is leaking around the thermostat or underneath the vehicle.

Engine Overheating

Here's how thermostats operate. The makers inject a mixture consisting of wax and ground brass into a container, which is known as a pellet. They then slide a highly polished metal rod through the silicone "O-ring" gasket and into the wax. The pellet is then sealed using a "crimp" ring.

Then, a metal "skirt" is welded around the pellet. If an engine gets cold, a spring pushes the skirt to an engine seat (just as a faucet that is closed) and stops the circulation of coolant. When the engine gets heated, the wax melts and expands.

Pressure increases until the point that the wax is trying to "spit out" the metal rod. The rod, however, is unable to travel anyplace. It's connected to the thermostat by a "bridge" on the other side of the thermostat.

The pellet eventually will move, overpowering the pressure of the spring. The thermostat then opens and lets coolant flow. The whole system is working perfectly until the rod begins to corrode. This rod that has corroded is damaging the seal made of rubber, and wax is released. When that happens, the thermostat stops opening; the cooling fluid and the engine start to overheat. The result could be catastrophic engine failure that could cost you many thousands of dollars.

Erratic Temperature Changes

Be aware of the temperature gauge on your dashboard. If the gauge's needle fluctuates between spikes and falls, a thermostat malfunction could be at fault.

Coolant Leaking

Examine the thermostat for leaks in the fluid. Coolant keeps your engine running at the proper temperature, but the absence of fluid could affect the efficiency of the engine.

How to Test a Car Thermostat

Before you remove the thermostat from your vehicle, verify the temperature and flow of coolant.

The cap of your radiator is removed and you can begin to run the engine. If coolant is flowing right away, the thermostat is closed. If it's slow to flow, it is best to wait until the engine starts to warm up. The coolant should be at the proper temperature before it begins to flow after about 10 or 20 minutes. If it doesn't begin to flow and you can see that your gauge's temperature increases, the thermostat is shut. If your coolant flows as it should, then there could be a second reason for your engine to overheat.

Replacing the Thermostat

If your thermostat is failing, do not just replace it and then top off the reservoir of coolant. It's warning you of a larger issue -- corrosion inhibitors within your coolant failed. Make sure to clean the system and replenish the coolant each time you change the thermostat.

Don't attempt to save some money by purchasing an inexpensive thermostat (about $5). High-end thermostats are constructed to withstand corrosion. The cost difference is minimal compared to possible damage to the engine. Some manufacturers even provide "fail-safe" models that fail when fully open to avoid overheating of the engine.