How to replace the thermostat
Custom Search

- In this page you will learn what a thermostat is, how it works and its location.
We will show you how to replace the thermostat in your car truck or SUV in this and the following pages with a step by step guide enhanced with pictures.

- What is a thermostat?
A thermostat is a device in your engine used to maintain a constant antifreeze/coolant temperature inside your engine.
Without a thermostat, the coolant in your car or truck would flow to the radiator all the time causing your vehicle to run below its operating temperature.
This would cause the following problems:
The car wouldn't be able to go in to closed loop due to the cold engine temperature, this translates in to higher emissions, poor fuel economy, and decreased engine efficiency.
Also in the winter your car would run so cold that your heater wouldn't work properly, causing the air expelled by the heater to be barely warm, if not cold.
So.......It is not good for a car to operate without a thermostat.

How do you diagnose a bad thermostat ?
There are two common problems associated with a bad thermostat, and they are:
This is the most desirable out of the two, because when you have a thermostat that is stuck in its open position, it will cause the coolant in your engine to circulate through the radiator all the time just like it would if your engine didn't have one, the way to know if your thermostat is stuck open is to start the engine when is cold, remove the radiator cap and look inside the radiator, if you see the coolant flowing, more likely the thermostat is stuck open, also, if you feel the temperature of the upper radiator hose, its temperature will be equal to your engine's temperature.

The least desirable of the two, this symptom will cause your engine to overheat extremely fast!!, causing a potential permanent damage to your engine like a blown head gasket, warped cylinder head(s) etc.
The way to diagnose a thermostat stuck in its closed position is to start the car and watch the temperature gauge in your dash, if it climbs to 3/4 and the thermostat is not open ; meaning that you can feel the temperature in the upper radiator hose and the radiator itself and it feels cold, while the engine's temperature is hot, stop the engine, you have a thermostat stuck in its closed position, ( assuming that your engine coolant level is normal), remember: A thermostat won't open if  the coolant level is low, because the way it is designed, the spring in the thermostat housing that makes it open and close, reacts to the antifreeze/coolant temperature, if the level is low, it won't reach the spring in the thermostat causing it to remain closed even if your engine is overheating, so make sure that your antifreeze/coolant level is in its normal level.

- Where is the thermostat located at?
Every make and model varies the location of the thermostat, but as a rule of thumb, it is usually located in the water outlet that leads to the upper radiator hose, very few makes and models have it reversed ( in the water outlet that leads to the lower radiator hose ), but there are some of them.
So, all you need to do, is follow your upper radiator hose, and locate the water outlet that is attached to the cylinder head, is very likely to have the thermostat in it.
Some vehicles equipped with a remote coolant reservoir, have the thermostat inside the radiator cap, and it is very easy to replace, just remove the radiator cap, and pull it out, the rest of the designs involve removing the water outlet.

Click on image to learn how to replace the thermostat               Click on image to learn how to replace the thermostat
on 1986-1989 Honda Accord equipped with 2.0 L Engine           on Dodge 5.2 and 5.9 L engines 

In this page we will show you how to replace the thermostat in a Nissan pick-up with a 2.4 L four cylinder Z engine, and remember, these steps apply to most makes and models, however, as we get them in our shop, we will document the process to perform this job in different makes and models, that way you will have specific instructions that fit your make and model.








  - Drain the antifreeze/coolant in a clean container by opening the valve located at the bottom of the radiator, you may reuse the coolant if it is clean, otherwise, this is the perfect opportunity to add new antifreeze, remember to keep the mix 50/50 ( 50% water, 50% antifreeze).

  - Once you have drained the coolant out, proceed to remove the upper radiator hose by loosening the hose clamp, once the hose clamp is loose, pull the hose out of the water outlet.

  - With the upper radiator hose removed, remove the two bolts that secure the water outlet to the cylinder head, and remove it from the vehicle, you may have to tap the water outlet housing gently with a rubber mallet it it is stuck to the cylinder head.

  - Once the water outlet is removed, proceed to remove the thermostat by pulling it away from the head.

  - Next proceed to remove the old gasket material from both, the water outlet and the cylinder head, a scraper works the best, once you have most of it off, use either a wire brush to remove the fine pieces remaining or fine grit sand paper, make sure that you don't over do this or you will damage the housing causing the water outlet not to seal and develop a water leak

  - After you have cleaned both surfaces and are free of old gasket material, proceed to install the thermostat in the cylinder head, follow by the thermostat gasket, the gasket you see in the picture has a self adhesive side, this made the installation so much easier, because the gasket will keep the thermostat in place as we get ready to install the water outlet.

NOTE:  IF you feel that the surface of either the water outlet or the cylinder head is either corroded or slightly damaged, use a slight coat of RTV silicone on both ends to ensure proper seal, otherwise, you will end up with a leak.

To finish this process, install the items back in the reverse order you took them off, next proceed to add the antifreeze mix to the radiator, start the car and allow it to run as you watch the temperature gauge, to allow the air trapped in the system, leave the radiator cap slightly opened so the pressure doesn't get to high due to the air in the system.
Also, keep a close eye in the temperature gauge, if you see the temperature rise above normal, stop the engine, and let it settle for a couple minutes, to see if the thermostat opens, if it still doesn't, allow it to cool down and start the engine again, this time raise the RPM around 2000 to 2500, this will allow the water pump to circulate the coolant inside the engine faster, that way if the level is low in the engine, it will splash enough on the thermostat causing it to open.

 Under no circumstances allow your engine to go over 3/4 of the temperature travel, if the thermostat hasn't opened you need to stop the engine, allow it to cool down for a few minutes, check the coolant level and do it again till the thermostat opens.