How to replace the thermostat — Honda Civic 2020

Tools you'll need

• Ratchet
• 10 mm socket
• Pliers
• Plastic gasket scraper
• Torque wrench
• Drain pan

Parts you'll need

• New thermostat for the 1.5L engine
• New thermostat gasket or O-ring
• Honda Type 2 coolant (about 1 gallon)

Steps

1. Cool the engine and drain some coolantLet the engine cool completely, then disconnect the negative battery terminal. Place a drain pan under the radiator and open the drain to let out enough coolant to drop the level below the thermostat housing.
2. Find the thermostat housing at the end of the upper hoseFollow the upper radiator hose from the radiator to the engine. Where the hose ends is the thermostat housing. Remove the air intake duct if it blocks your view.
3. Remove the hose and the housing coverLoosen the hose clamp and pull the upper radiator hose off the housing neck. Then remove the two or three bolts holding the housing cover and lift the cover off.
   Tip: Have a rag ready. Coolant will spill when you pull the hose and the cover off.
4. Remove the old thermostat and note its orientationLift the old thermostat out and note which way it was facing. The spring side goes toward the engine, and the small jiggle valve should sit at the top. Take a photo before you remove it.
   Tip: Installing the thermostat backwards is the most common mistake on this job. The spring always faces into the engine.
5. Clean the gasket surfacesScrape the old gasket material off the housing and the engine surface with a plastic scraper until both are clean and smooth.
6. Install the new thermostat and refit the coverSet the new thermostat in place the same way the old one sat, with the jiggle valve at the top, and fit the new gasket or O-ring. Refit the housing cover and tighten its bolts evenly to about 9 ft-lb. Do not overtighten them.
7. Refit the hose and refill the coolantPush the upper radiator hose back on and tighten its clamp. Refill the cooling system with Honda Type 2 coolant and refit the radiator cap.
8. Bleed the air and verify the temperature and heaterReconnect the battery, start the engine, and turn the heater to full hot. Watch the temperature gauge climb to normal and stay there, and check that the heater blows hot air. Top off the coolant as air bubbles work out, then check around the housing for leaks.
   Tip: If the gauge stays cold or the heater blows cold, there is still air trapped in the system. Let it cool, top it off, and run it again.

Safety first

Never open the cooling system while the engine is hot. Hot coolant can scald you badly. Do not overtighten the thermostat housing bolts; the housing is aluminum and the bolts can strip. If you are not confident, have a qualified technician do this job.