Car thermostats 101

In order for your car’s engine to stay at a good operating temperature, it uses a thermostat to regulate the flow of coolant. But if your thermostat is broken, it can be a bit like Goldilocks; your engine could run too cold or too hot (both are bad news).

So how do you know if it’s faulty? Let’s look at how it works, and what to do if it doesn’t.

What is a thermostat in a car?

For your car’s engine to run properly, it needs to be kept at a certain temperature. The car’s cooling system looks after this, and one of its most crucial parts is the humble thermostat.

Located between the radiator and the engine, its job is to make sure that the car’s coolant goes where it’s needed, so that the engine can run at a safe and optimal temperature.

How does a car thermostat work?

The thermostat is a mechanical device that opens and closes when it gets hot and cold.

Older thermostats are valves that contain a cylinder filled with wax, however newer vehicles have electronically controlled computer regulated thermostats for greater operating control.

In the older models - one side of the valve reaches a certain temperature, it melts the wax, expanding the cylinder. This cylinder pushes against a metal coil that opens the thermostat. When the wax cools down again, it shrinks, allowing the thermostat to close.

It works like a gatekeeper to your radiator. When your car is cold, it stays closed in order to keep the coolant circling around your engine until it reaches a particular temperature. This means that your car warms up quickly to its optimum temperature.

Once the coolant warms up, the thermostat opens and lets the coolant circulate through the radiator. The radiator then cools it down so that it can flow back to your engine and keep it from overheating.

You can see what an essential role it plays in your car’s cooling system.

How do you know a thermostat is bad?

There are a few tell-tale signs that your thermostat may have given up the ghost and needs replacing, so keep an eye out for the following symptoms:

How to test a car thermostat

A quick way to test if your thermostat is faulty is to open up the hood and let your car idle. While the car is cold, take off the radiator cap (never do this while the car is hot, as hot coolant and steam will spray out under pressure) and see if any coolant is flowing. It shouldn’t be moving, as the engine is cold, so if you see any coming in then it’s a sign that your thermostat is stuck open.

If coolant isn’t flowing, leave the car running until it gets to optimal temperature, and see if any coolant begins to flow. If it doesn’t, then it’s still closed and is stopping your engine from cooling down. You’ll also be able to see your temperature gauge rising and engine thermostatic fans kicking in.

You can also feel the upper and lower radiator hoses. When the car has been driven and gets hot, pull over and turn off the engine. Lift up the bonnet and carefully feel the top radiator hose, which should be hot. If the bottom radiator hose is completely cold though, it means that the thermostat is stuck closed and isn’t letting coolant circulate. Do this with caution, and always use personal protective equipment.

Can I run a car without a thermostat?

Your car will still run with a broken thermostat, but it’s not advisable. Driving with a faulty thermostat can drastically reduce your car’s performance and cause other more expensive issues down the line.

If your car runs too cold you’re looking at bad fuel economy and engine wear, and if it runs too hot you can be looking at cracked hoses, or even a broken head gasket which means taking the whole engine apart to replace it or even a completely new engine if it’s overheated badly enough!

So now you know how important a car’s thermostat is and how to test if it’s faulty, you’ll be able to tell when you need a new one.

If you need a thermostat repair or replacement, make a booking with one of your local mycar mechanics today. They’ll diagnose and fix any of your car’s cooling system problems.