Hopefully, by the end of this Instructable, you'll be able to replace your own broken thermostat (you're probably throwing a P0128 code if you're here). You can watch the linked video if you need any more visual references, but the text will be more detailed!
Step 1: Tools
You probably won't have to go out and buy any new tools, all that's needed is:
- A new thermostat, we got ours super cheap from RockAuto.
-Jack and jack-stand
-Honda Type 2 Coolant/Coolant of your choice (5.14L if you do a full swap, or just 1 jug if you're only going to top up)
Step 2: Jack Up the Car
When jacking up the car make sure to use the jacking points, the image uploaded is for an 8th gen civic sedan, but for the RSX it's very similar.
Step 3: Remove the Bumper
Now it's time to remove the front bumper, you're going to need your flathead for this part. After you remove the front bumper, make sure to take off the splash-guard too.
Step 4: Drain the Coolant
This step isn't necessary if you're not going to do a coolant swap, but you might as well because you're going to lose a lot of coolant when you take the old thermostat off. To do this step, turn the part labeled "drain plug" in the linked image counter clockwise and coolant will begin to drain from the bottom of the rad. Make sure to have a big drain-pan ready.
Step 5: Remove the Hose Connected to the Thermostat
Use your pliers to pinch the hose-clamp. While the clamp is pinched, slide it off the hose that's fitted to the thermostat. Slide the hose off the thermostat, this may take some elbow grease. If it refuses to come off try wriggling the hose back and forth.The second attached image shows the clamp if you're having trouble finding it, but it's right on the thermostat and hard to miss.
Step 6: Remove the Thermostat
This part can get really tricky if you have big hands; Since you're accessing the thermostat from the bottom of the car and not the top (the top requires removing the intake manifold). Remove the 3x 10mm bolts that connect the radiator to the motor. The bottom two are easily removed, but the one on top can get tricky since you're kinda doing it blindly. A friend with small hands for this part will help things go smoothly. If you're having trouble finding where the bolts are or need a little bit of a visual reference, refer to 7:42 of the video linked in the intro.
Step 7: Install the New Thermostat
This part is essentially the previous step but in reverse. Put the new thermostat on in the reverse order that you took the old one off. Reattach the hose you removed, and make sure you fasten it again with the hose-clamp.
Step 8: Enjoy Your New Thermostat!
After you put your car back together (same steps as before but in reverse order), enjoy your RSX that hopefully isn't throwing a P0128 code anymore. Make sure that you top up your coolant because you probably lost some when you took off the thermostat, and if you did a full swap even better! If you run into overheating issues afterwards you may have air in the coolant system, to remedy this: burp the coolant system.