How to Replace a Thermostat

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A thermostat is a tool that regulates heating and cooling, whether it be in your home or in your car. Replacing inefficient thermostats can help you save money on utility bills or, in your vehicle, keep you safe on the roads. Whatever your situation, replacing it yourself is a task that is surprisingly simple. See Step 1 of your preferred method below.

Replacing a Thermostat in Your Car

  1. Make sure your car has cooled down.It won’t be a good day if you singe off your eyebrows and get third-degree burns on your hands, so turn off your car and let it cool down before you open up the hood and get to work. Let it sit for at least an hour before you start dissecting its parts.
    • It’s not a dumb idea to protect yourself with goggles or gloves, either. If you don’t want anything getting in your eyes or your hands getting covered in gunk, get out the protective gear. And, of course, a shirt you don’t mind smudging with grease or oil.
  2. Drain the antifreeze out of your car.The thermostat and radiator hose are linked to your car’s cooling system; if you don’t drain out the coolant, you’re gonna get water everywhere when you start disassembling. Here’s how:
    • Place a bucket (or some sort of container) underneath your radiator. You’ll have somewhere between 4 to 8 cups of fluid pouring out, so don’t skimp on the size of your container.
    • At the bottom of the radiator, there should be a draining screw or cap (technically, it’s a radiator drain cock). Twist this to the left, opening it up.
    • Let all the water and coolant flow out. Keep the cap somewhere you won’t lose it.
  3. Locate your thermostat.Every model of car is different. Some thermostats you could spot from a mile away, others will be an obstacle to even the most trained of eyes. If looking at your car’s engine is like reading gibberish, find the radiator hose and follow it to the end — that’ll be where your thermostat is located.
    • The body of the thermostat is probably metal with a bit of gold in the center and possible a rubber ring around the edges. It resembles a top or dreidel in shape and size.
    • If you’re not quite sure what you’re doing, consult your manual or look up the location online. It’s better to know what you’re looking for instead of poking around and possibly injuring yourself.
  4. Remove the radiator hose and take apart the thermostat casing.The hose is most likely clamped to the thermostat casing. Unscrew this and set it aside. Move onto the thermostat casing, exposing the thermostat itself. You will definitely need a screwdriver, and you may need pliers, for the record.
    • Most vehicles have a two-bolt or three-bolt system for the thermostat casing.
    • If corrosion and gunk is building up prominently, clean up the area before you go about adding your new thermostat.
    • A bit of water will probably come out with removal of the hose. This is normal.
  5. If desired, test your thermostat. Is it possible that your thermostat works, it’s just stuck closed or a differentpart of your vehicle is starting to kick the bucket, affecting your thermostat’s ability to make accurate readings? If so, it’s very easy to test your thermostat. Here’s how:
    • Get a pot of water boiling.
    • Insert your thermostat. The thermostat should open at around 190 ºF (88 ºC). Since water boils at 212ºF (100ºC), this is more than enough.
    • If the thermostat doesn’t open in the water (and then close when it cools), you need a new one.
  6. Swap out your old thermostat for the new one.From here on out, it’s mainly a matter of reassembly — the easy stuff. Replace your thermostat just like it the old one was positioned. If applicable, replace the rubber ring, too, sealing the edges.
    • If the area is building up dirt and grime, wipe it down with some cleaner first. You want to maximize the life of your thermostat and not have to deal with this again anytime soon.
  7. Reassemble the system.You remember what everything looked like, right? Here’s a brief checklist:
    • Make sure the thermostat is snug and in place.
    • Bolt down the thermostat casing over top of the thermostat. Finger start your bolt and then bust out your pliers or socket wrench and get to tightening. Be careful not to strip the bolts.
    • Replace the radiator hose and clamp. The radiator should be snug on the outside of the thermostat casing and the clamp should be nice and snug.
  8. Replace the coolant and check for leaks.If the coolant you just drained out was fairly new, just use the same stuff in the bucket and add it back in. If it was old, you may be better off throwing the contents of the bucket out and just using new coolant. Either way, replace the coolant and make sure the radiator drain cock is on tight.
    • Once replaced, check for leaks. Your car needs coolant to operate safely. If yours is leaking, you literally won’t get very far.
  9. Get back on the roads. You’re done! Now all you have to do is keep an eye on your temperature gauge. If it’s acting up, do a double check to make sure you secured everything appropriately. If so, you may need to consult a mechanic — the problem probably lies elsewhere.

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