How much does it cost to replace a car thermostat? (2026)

The thermostat in your car’s engine is a small but vital component. It regulates the engine's temperature by allowing coolant to flow into the radiator when needed. Thermostat issues can be worrying because they can often mimic a blown head gasket. 

Thankfully, thermostats are a relatively cheap problem to fix, but can easily develop into something worse if left unattended. In this article, we’ll take a look at how much thermostat issues cost to repair, how to detect them, and when you should get them fixed.

How much does it cost to replace your engine's thermostat?

Like all car repair costs, thermostat replacement can vary depending on the type of car and what type of garage you take it to. 

What are the symptoms of a failing engine thermostat?

A broken or sticking thermostat produces some tell-tale symptoms:

• Fluctuating engine temperature

• The engine never reaches operating temperature (always cold)

• No cabin heating

• Decreased MPG

• Error lights or messages on the dash

How to tell a broken thermostat from a head gasket issue

The symptoms of a broken thermostat can be similar to those of a damaged head gasket, so it’s important to take note of all the symptoms before worrying too much.

A failing head gasket is usually accompanied by one or more of the following, whereas a faulty thermostat would not:

• Mayonnaise-looking sludge in the oil

• Steam from the exhaust

• Loss of coolant

• Loss of engine power

A good test to do to rule out a head gasket issue is a block or combustion leak test. This cheap kit uses a special liquid that changes colour when it comes in contact with exhaust gases. 

What does a thermostat do?

In general, a thermostat is a device that regulates the temperature of a system, be that inside a room, or in this case, of an engine. They are in effect, a heat-controlled valve, allowing coolant to flow through the radiator.

The radiator removes heat from the coolant, in turn cooling the engine. If the thermostat sticks closed, the engine will not be able to shed the excess heat. If it sticks open the coolant will constantly flow through the radiator, preventing the engine from reaching operating temperature. 

Up until recently, most cars’ thermostats were entirely mechanical, using a piece of expanding and contracting wax, to open the valve. In many modern cars though an electronic thermostat is used, which allows more precise control.

How important is repairing an engine’s thermostat?

Despite the thermostat being a small and relatively inexpensive part, its role is crucial to the health of the engine. An engine with a stuck-open thermostat will perform inefficiently and eventually run poorly. 

An engine with a thermostat that is sticking in the closed position is on borrowed time. Without adequate cooling, the engine can easily overheat. If this goes unnoticed, the engine heat can do serious damage, such as warping heads and cracking engine blocks.

Repair your thermostat with Bumper

Whether your car's issue is the result of a stuck thermostat or something far worse, Bumper can help with the cost. Rather than paying up front, Bumper’s interest-free car repair finance allows you to split the cost of repairs into monthly payments. Apply online or at the garage or dealership.