How to Replace the Thermostat on Honda Carsby Contributing Writer
The thermostat in your Honda car has a small, wax-filled cylinder in the middle. When hot, the wax expands and opens the thermostat, letting hot coolant from the engine flow into the radiator to remove heat. With years of service, this mechanism fails, blocking or allowing coolant to flow freely and permanently. Either way, engine performance is compromised. However, stuck coolant will cause the engine to overheat and, given enough time, melt internal components. Replace the thermostat as soon as possible in your Honda car and prevent expensive repairs down the road.
Under The Hood:
- How to Replace the Thermostat on a Honda CRV
- How to Replace the Thermostat in a 1998 Honda Accord
- How to Replace the Thermostat in a 1998 Honda Civic
- How to Replace a Thermostat in a 2001 Honda Civic
- How to Change the Thermostat in a Honda Prelude
- How to Change the Thermostat in a Honda Accord
Locate the thermostat housing cover by tracing the radiator cover, which extends from the top of the radiator to the right side of the engine. The CRV engine is installed sideways, so the right side faces the radiator. The thermostat housing is coupled with the radiator hose.
Remove the bolts from the thermostat housing cover with a 10 mm wrench. Pull the thermostat housing up and away from the base of the engine. Leave it connected to the radiator hose, but push it off to the side so you can access the thermostat.
Pull the thermostat out of the engine. It's not bolted into place, so it can be pulled right out. Locate the thermostat housing gasket on the base of the engine. Pull it off, and throw it away.
Place a new gasket in place, and set the thermostat back into the CRV engine. Be careful not to get the gasket wet--that could cause a leak.
Place the thermostat housing cover back onto the engine, and bolt it into place. Warm the engine up, then check for any leaks. If there is a leak, tighten the cover down more. This should eliminate any leaking.
Items you will need
Honda CRV thermostat
Honda CRV thermostat gasket
10 mm wrench
Park your Accord on a flat surface. Concrete or asphalt is recommended. Pop your hood and disconnect the negative battery cable.
Let the engine cool for at least 30 minutes prior to beginning the procedure.
Locate the radiator drain plug underneath the front of the engine bay. Position a sealable container underneath it to let the engine coolant drain.
Use the flat head screwdriver to remove the drain plug. Let the coolant drain for 15 to 20 minutes, and then set the container aside.
Loosen the bolt around the upper radiator hose clamp where it connects to the engine. Remove the clamp, and then pull the hose away to expose the thermostat housing.
Remove the two (2) bolts from the thermostat housing, and then slide the housing off to expose the thermostat and gasket.
Pull the thermostat and gasket from the its mount and set them aside.
Attach the new thermostat gasket around the new thermostat. Apply a small amount of anti-seize lubricant around the thermostat threads.
Position the new thermostat in its mounting place, with the bleed hole pointing upward. Reattach the upper radiator hose and secure the clamp.
Turn the bleed valve near the thermostat housing 1/2 turn (for 2.3 L engines only).
Replace the radiator drain plug, and then refill the cooling system. Reconnect the negative battery cable, and then start the engine and check for leaks.
Items you will need
Flat head screwdriver
Sealable container (such as a drain pan with lid)
Drive the Honda Civic onto a set of ramps and secure the parking brake. Raising the front of the Civic allows more room to work under the engine.
Place a drain pan under the petcock located on the bottom of the radiator. Open the petcock by placing a 1/4-inch ratchet driver onto the petcock and turning it counterclockwise. Drain the coolant into the plan. Close the petcock once all of the fluid drains from the radiator.
Follow the lower radiator hose from the bottom of the radiator to the point where the hose connects to your Civic's engine. The hose connects to a small metal housing, which holds the thermostat inside the engine block.
Remove the radiator hose from the thermostat housing by squeezing the two metal tabs together with a pair of pliers. This releases the clamp's pressure on the radiator hose. With the pressure released, pull the hose off the housing.
Remove the two bolts that secure the thermostat housing to the lower block by using a ratchet and 12mm socket.
Pull the thermostat housing off the lower engine block. The thermostat and thermostat gasket come off with the housing. Remove the used thermostat and gasket.
Scrape the bottom of the thermostat housing and the mating surface of the Civic's engine block with a wire brush or metal scraper until both are clean.
Place the spring end of the new thermostat inside the engine block, and hold it there with one hand.
Place the thermostat gasket over the thermostat, and hold both in place with your hand.
Place the thermostat housing over the gasket and thermostat, and secure it with both 10mm bolts.
Slide the radiator hose back onto the thermostat housing, and secure it with the radiator hose clamp.
Remove the radiator filler cap located on top of the radiator. Pour the coolant back into the radiator. Put the radiator cap back on.
Items you will need
1/4-inch ratchet drive
Removing the Old Thermostat
Place a clean drain pan under the radiator in the direction of the drain valve. Insert one end of a 12-inch clear, vinyl hose into the drain valve and point the other end to the drain pan.
Loosen the radiator cap and open the drain valve by hand. Allow the coolant to drain completely. Close the drain valve and remove the hose. Cover the drain pan to keep the coolant clean for later reuse.
Shift the transmission to Neutral and release the parking brake. Jack up the front of your Honda Civic with a floor jack. Place a jack stand under each side for support. Chock the rear wheels.
Put on a pair of safety goggles. Crawl under the front of your Civic and remove the engine splash shield from the bottom with a ratchet and deep socket.
Depress the clamp tabs holding the lower radiator hose to the thermostat housing at the engine side. Slide the clamp about five inches toward the radiator with a pair of rib-joint pliers. Pull the lower radiator hose off the thermostat housing by hand.
Unfasten the two bolts (1.7L engine) or three bolts (2.0L engine) securing the thermostat housing to the engine with a ratchet, short ratchet extension and deep socket.
Separate the thermostat housing from the engine. Remove the O-ring seal and thermostat from the engine opening. Look at the mounting position of the thermostat, if you are working on a 1.7L engine.
Installing the New Thermostat
Clean the engine block opening and thermostat housing mating surfaces with a plastic scraper, if necessary. Position the new thermostat in place with the pointed side toward the thermostat housing and install a new O-ring seal. On the 1.7L engine model, make sure the pin located on one side of the thermostat is at the 12 o'clock position.
Replace the thermostat housing and install the two bolts (1.7L engine) or three bolts (2.0L engine) finger-tight to secure the thermostat housing to the engine. Tighten the bolts to 9 ft.-lbs. (12 Nm) on the 1.7L engine or 7 ft.-lbs. (10 Nm) on the 2.0L engine with a torque wrench, short ratchet extension and deep socket.
Replace the lower radiator hose on the house thermostat fitting. Secure the hose to the housing with the clamp using the rib-joint pliers.
Reinstall the engine splash shield with the ratchet and deep socket.
Raise your Honda Civic above the jack stands. Remove the jack stands and lower the car to the ground. Apply the parking brake and remove the chocks from the rear wheels.
Place a small funnel in the radiator neck. Pour the coolant you previously removed and tighten the radiator cap.
Start the engine. Check for coolant leaks around the lower hose and the thermostat housing.
Items you will need
Clean drain pan
12 inches clear, vinyl hose
2 jack stands
2 wheel chocks
Deep socket set
Short ratchet extension
Raise the front of your Honda Prelude with a jack and lower it onto jack stands, or use wheel ramps. Loosen the drain plug located at the bottom middle of the radiator. Drain the coolant into a suitable container. Reuse this coolant if relatively new and clean.
Twist slightly and pull the intake air duct from the air cleaner on top of the engine. Disconnect the two halves of the duct where it meets in front of the thermostat housing and remove that section of the duct.
Follow the upper radiator hose to where it meets the thermostat housing. Loosen the clip holding the hose to the housing and pull off the end of the hose from the thermostat housing. Take out the two bolts holding the thermostat housing cover. Note the position of the old thermostat and remove it. Install the new thermostat in exactly the same position, spring-side facing the engine.
Clean any residue from the old gasket off the inside of the housing cover. Install the new gasket. Apply a silicone sealer around the thermostat prior to installing, if desired.
Reinstall the thermostat housing cover, upper radiator hose and air duct. Fill the radiator with reserved or new coolant. Use a wrench to open the bleeder bolt located near the thermostat housing. Fill the radiator and tighten the bleeder bolt when you see coolant begin to spill from the bleeder.
Start your Honda Prelude and run with the heater blowing on high until the engine warms up. Feel the upper radiator hose to ensure it is getting hot. Check for leaks where the radiator hose meets the thermostat housing. Tighten the clamp holding the hose to the thermostat housing to stop any leaks.
Items you will need
Jack and jack stands or wheel ramps
Socket or open-end wrench
Thermostat and gasket
Silicone sealer (optional)
Pliers (if needed)
Remove the Thermostat
Make sure that the engine and radiator are completely cool. Jot down the radio security code and any station pre-sets. Disconnect the battery ground cable.
Drain the coolant from the engine to a level below that of the thermostat. Use a sealable container to store the coolant.
Release the tension on the clamp on the hose to the thermostat housing with a pair of pliers. Take the hose from the thermostat housing.
Loosen the fasteners that hold the thermostat housing in place. Take out the housing then remove the thermostat.
Install the Thermostat
Set the new thermostat in place with a new seal. Position a thermostat with a bleed hole so that the bleed hole in on top.
Use an anti-seize compound on the threads of the fasteners before installing them. Set the thermostat housing in place and tighten the retaining bolts.
Connect the hose to the thermostat housing. Secure the hose with the clamp. Set the heater to the "full hot" indicator. Open the coolant bleed vale (near the thermostat housing) a half-turn.
Fill the cooling system and the overflow reservoir with the recommended coolant in a 50/50 mix of distilled water to prevent the build up of mineral deposits in the system. Bleed the lines to remove any air pockets.
Make sure all the hoses and fittings are properly positioned and installed. Close the bleed valve.
Reconnect the battery ground cable. Set the radiator cap on the radiator but do not tighten it. Start the engine and allow it to run until the cooling fan has passed through two cycles.
Turn off the engine. Add more coolant as needed. Tight the cap on the radiator. Restore the radio security code and station pre-sets.
Items you will need
Mechanic's toolset, including a full socket set, wrenches and screwdrivers
Replacement thermostat, new or rebuilt
New gasket for thermostat