How much does a new thermostat cost?

Coolant £2 per litre
Thermostat £5-£80

How much could I save by replacing my own thermostat?

Thermostat replacement normally involves the removal of other parts, such as throttle housing and throttle body, as well as draining and refilling the cooling system, but should take a home mechanic around a couple of hours or so. A main dealer can charge you up to around £150 per hour's labour to fit a new thermostat, and you're unlikely to get much change out of two £50 notes by getting the job done at an independent garage, so this is a job well worth doing yourself, with a Haynes Manual by your side.

Find a manual for your car here and start saving with Haynes

How a car’s thermostat works

can car thermostat get stuck open

A thermostat controls the engine’s coolant temperature and stops the motor from overheating. When the engine is cold the thermostat is closed, preventing coolant from leaving the engine block. This helps the engine to warm up as quickly as possible, boosting its efficiency and lowering emissions and fuel consumption.

Once the coolant temperature reaches around 180F, wax inside the thermostat melts and a rod is pushed out, opening the valve and allowing the coolant to begin circulating.

This task requires some experience, uses basic tools, and will take two to three hours, depending on your model.

When to replace your thermostat

“You may find that the heater in the cabin doesn’t blow out hot air and fuel consumption will increase”

Symptoms of a thermostat stuck in the open position include the engine running cold, or at least not getting up to temperature. You may find that the heater in the cabin doesn’t blow out hot air and fuel consumption rises.

If the thermostat is stuck closed it will prevent water in the engine jacket from reaching the radiator. The engine will overheat (often quite quickly) and start running poorly. There’s a danger that the head gasket will fail, along with other seals - stop the engine immediately and replace the thermostat as soon as the engine is cool.

All cars are slightly different, so if it is time to change your thermostat, use our before-you-begin checklist, and find your car for specific instructions.

How to change your thermostat

Watch this video to see how it's done. Find the full step-by-step task for your model.

A very brief summary of the task:

  1. Make sure the engine is cold and raise the vehicle on jackstands
  2. Drain the coolant. Remove and examine the hose(s)
  3. Remove the thermostat housing
  4. Remove the old gasket/seal and replace with new
  5. Install the new thermostat and refill the system

Why you should replace your thermostat

Why you should replace your thermostat

A failed thermostat will prevent the engine from operating within its ideal temperature range and affect its performance. This can be dangerous.

A thermostat stuck open allows water to flow into the radiator all the time. This means the engine will take longer to warm up and may not reach the correct operating temperature at all. As a result your engine will use more fuel and will emit more CO2.

A thermostat stuck closed is more dangerous. It prevents water from leaving the engine jacket and reaching the radiator, where it is cooled. The engine temperature will rise rapidly, putting stress on the head gasket and other seals, and potentially causing the engine to fail. Pull over and turn off the engine as soon as possible.

Tools you will need

Only basic tools are required for this job, although you may need to raise the car to remove the undershield.

  • Floor jack (if necessary). Not your car’s emergency jack
  • Axle stands
  • Ratchet and socket set
  • Flat-bladed/Phillips/torx screwdriver
  • Rags
  • Plastic scraper

Parts you may need

  • Coolant - If it’s in good condition you may be able to reuse it
  • New thermostat - You may also need to replace the housing
  • O-ring seal(s)/housing seal(s)/gasket