How to Replace a Honda Civic Thermostat

How to Replace a Honda Civic Thermostat


Responsible for keeping your engine from overheating, the Honda Civic thermostat also maintains your operating temperature. By keeping your coolant temperature in the operating range, this allows your Honda to run optimally and get the most performance and gas mileage.

Thermostats are basically valves that use a wax pellet to regulate engine temps. Once the coolant in your engine warms up to a certain temperature this pellet allows the valve to open. The coolant is now allowed to flow into your radiator and through the rest of your cooling system.

When your Honda Civic thermostat is beginning to fail, there’s a few classic symptoms. One of which is when the thermostat is seized or stuck closed, which is very common. This prevents the liquid in your engine from flowing into your radiator and your Honda Civic will overheat. Because the SOHC VTEC engine in your Civic is made from aluminum, once it warms up enough it will cause your cylinder head to warp.

Another one of the more common problems with the thermostat is when it sticks OPEN. Because it fails to close or seal, your Civic engine will never properly warm up which can cause even more problems. When your engine operating temp is far too low, your ECU will constantly keep you on the “warm-up” map, which will cause your engine to run rich. If you are not sure what lean or rich conditions are, check out our primer on closed loop operation and how it affects your gas mileage.

If you need help servicing or replacing your Honda Civic thermostat, you can use this handy guide to get the job done. The first order of business is of course to secure the vehicle, and drain the car of coolant. Make sure to dispose of the coolant properly and follow all the safety guidelines whenever you are working on your Civic.

Today’s test vehicle is a 1997 Honda Civic DX and we’ll be replacing the thermostat part number 19301-PAA-306. This vehicle is equipped with the SOHC D16 engine, a 1.6 liter non-VTEC engine. Once you have the coolant drained from your engine, you can begin our how to guide on how to replace a Honda Civic thermostat.


The thermostat housing on your Honda Civic is located behind the distributor and mounted just above the starter. When the coolant is drained from your vehicle, go ahead and disconnect the engine coolant temperature sensor as shown.

There is a 10mm bolt that’s underneath this sensor, that secures a series of engine ground straps. Remove the 10mm bolt there and disconnect the grounds now, and you can now access the two 10mm bolts that hold the upper half of the thermostat housing in place.


Now that these grounds are removed, you can begin removing the two 10mm bolts that hold the upper housing. Once you have these 2 bolts taken out, can you pull off the thermostat housing, you can leave the radiator hose connected.


Now you can yank out that old Honda Civic thermostat, and you can begin prepping the thermostat housings for the re-installation process.


Now that you have the old unit removed, you must thoroughly dry the lower and upper halves of the housing. Use Hondabond or high-temp RTV silicone gasket maker once both surfaces are dry. Prepare your new thermostat using the rubber isolator, and rub the gasket maker or Honda bond until it gets tacky.

Gently reinstall your new thermostat and use both 10mm bolts to secure the housings in place. You are now done with your new thermostat installation, make sure to allow your gasket maker to dry and cure before pouring new coolant in.

Have any questions about our How to guide on replacing this Honda thermostat? Leave us your comments below and let us know!