How to Replace a Car Thermostat

How to Replace a Car Thermostat

A thermostat controls the flow of hot coolant from the engine to the radiator for the cool down process. A faulty thermostat can disrupt the flow of coolant inside the engine, causing it to overheat or cool down. Luckily, replacing a thermostat is an inexpensive and easy task. All you need is a new thermostat and 20-25 minutes. However, knowing when the change is required is equally important. Read along to learn when and how to replace a car thermostat and prevent your engine from suddenly overheating.

Signs of a Faulty Thermostat

Although an overheated engine is one of the signs of a bad thermostat, an engine can overheat due to many other reasons.

The signs below can help you identify a faulty thermostat instantly.

One of the first signs you can notice in case of a bad thermostat is that the needle on the temperature gauge is either very high or keeps on fluctuating. If the needle stays beyond the ¾ mark of temperature gauge, you are likely experiencing a fault with the thermostat.

Another sign of a bad thermostat is that the engine remains cold. Since the flow of the coolant stops being regulated, the coolant keeps flowing in the engine, causing it to cool down and not function properly.

A faulty thermostat may also cause drastic changes in the coolant levels. Check the coolant tank and notice if the coolant is present in the right amount. Top up the coolant tank with a new antifreeze coolant if required and observe if the level remains the same or not. If the level fluctuates or the coolant overflows beyond the marked level, there is likely a problem with your car’s thermostat.

Before you can replace the thermostat, it is essential that you drain the coolant out of the car first. Replacing the thermostat with the coolant still inside the system will cause the coolant to gush out and spill everywhere. The coolant is an extremely toxic fluid, which is bad for small animals and the environment in general. It is thus advisable to drain the coolant out in a controlled manner and discard it carefully without damaging the environment.

Draining the Coolant

Knowing how to drain the coolant is as equally important as knowing how to replace a car thermostat. You need to put a draining pan or a bucket underneath the draining valve. You can jack the car up on a car lift for easier access to the valve. If the valve is not there, you can unclamp the lower hose from the radiator and let the coolant flow out from there. Collect the liquid in empty bottles and label these bottles toxic. Drop them off at a chemical waste management facility.

Flushing the Car’s Cooling System

Once the coolant has been drained, this is a good opportunity for you to deep clean the cooling system by flushing the system. Turn on the ignition and put the car heater on full blast. Turn off the draining valve if open. Now pour a good radiator flush inside the car from the radiator’s opening and let it run through the system before reopening the draining valve and letting the fluid gush out. The process can be repeated as required. This fluid contains toxic residue of the coolant; discard it responsibly.

Replacing the Thermostat

Things required

Replacing a thermostat is a simple task that requires:

  • A ratchet
  • A new thermostat
  • A pair of pliers
  • A new gasket
  • A new antifreeze coolant

Removing the old Thermostat

You will have a very narrow pathway to work on the engine block; work carefully so that you don’t damage other components of the car. Follow the steps below for removing a thermostat.

  • Firstly, you need to locate the thermostat. The thermostat is encased in a plastic housing, bolted to the engine block, and connected to the upper radiator hose that gets the coolant from the radiator to the engine.
  • To have better access to the housing, you need to unclamp the radiator hose. Make sure you remove the clamp gently without tearing the hose, which is very prone to damage.
  • You now need to open the bolts that keep the housing in place. You can use a ratchet of an appropriate size and remove the bolts.
  • Now you can remove the housing. You will find the thermostat inside the housing in case it’s broken. Otherwise, a part of it might be stuck inside the engine block opening. If stuck, use a pair of pliers to pull it out.
  • Make sure that you remove the old gasket as well.

Putting in a New Thermostat

Before replacing a thermostat, ensure you have the accurate dimensions of the thermostat and the gasket; otherwise, your car will not function properly, and the whole process will go to waste. Notice the pressure ratings on the old thermostat and get a new thermostat of the same pressure rating and design and a suitable gasket.

  • You need to scrape off any remains of the old gasket from the housing and the opening of the engine block with a scrapper carefully. Make sure the remains don’t fall inside or that you don’t end up damaging the housing or the engine block with the scrapper.
  • Now place the new thermostat with the spring side and the valve side pointing up.
  • Place the new gasket over the thermostat on the opening of the engine block. It is necessary to ensure that the gasket does not cover any holes where the bolts need to be fixed.
  • Now place the housing back and use a ratchet to put the bolts back in.
  • Attach the hose back in and clamp it.
  • Now with the thermostat in place. You need to top up the antifreeze coolant mixture inside the cooling system. It might also be the right time to add some engine oil to the engine to increase its efficiency.

Start your car and take it for a drive. You’ll notice that the temperature gauge is back to normal.


The simple procedure of knowing how to replace a car thermostat can save you an unnecessary trip to the mechanics and can significantly improve your engine’s output.

If the overheating problem persists, you might want to check your car for coolant leaks, especially the hoses and radiator cap that are most prone to wear and tear. In case of a radiator leak, a good radiator stop leak or a rust converter can fix minor leaks for some time, but eventually, you’ll have to get a new radiator.