How To Replace Your Evolution Thermostat

How To Replace Your Evolution Thermostat


Temperature inconsistencies in your engine can lead to serious problems, and the 4G63 is no different in this regard. There’s a variety of OBDII trouble codes that can arise from a faulty thermostat, from P0125 Mitsubishi Insufficient Coolant Temperature for Closed Loop operation, to P0128 or P0137.

When you have your Malfunction Indicator Lamp (MIL) or check engine light on, you may need to replace your thermostat.

Today we’ll be showing you how to replace your Evolution thermostat and restore the proper operating temperature in your turbocharged 4G63. You should always maintain the proper maintenance on your Mitsubishi Evolution cooling system to prevent overheating issues and blown head gaskets.

Our test vehicle is a 2005 Mitsubishi Evolution VIII with the 2.0 liter 4G63, and we’ll be replacing it with Mitsubishi part number MN143463 which is also MD310106. This very same thermostat can also be found under MD328070, MD332446, or MD337408.

To begin our How To Replace Your Evolution Thermostat Guide, open your hood make sure you are working on a cool engine. It is not required for you to disconnect your battery, although it wouldn’t hurt to be safer than sorry.

You can save yourself some money if you know how to replace your Evolution thermostat, and the first step is to disconnect your PCV hose from your valve cover.


If you have your stock upper intercooler pipe in place you will need to disconnect and remove it. Check our How To guide on installing a aftermarket intercooler kit on a Evolution to learn how to do this job. Since we have an aftermarket pipe in place already, we’ll be disconnecting that ahead of time.


There are three 10mm bolts that secure the upper thermostat housing to the lower neck. A metal bracket is located on the back of this housing, and you must drain your radiator a bit before you begin. Open your radiator by unscrewing your cap and then rotate your radiator petcock to slightly drain coolant from your cooling system.

Now undo the three 10mm bolts and then pull up on the upper radiator hose to remove the upper thermostat housing.


If you have drained enough coolant, there should be no coolant that spills out making the job much easier. This is a easy tip that should be a part of everyone’s process on replacing your Evolution thermostat.


Remove your old thermostat and discard and then drain the coolant to a lower level if there’s too much in the upper neck.


Dry the aluminum lower housing completely and then apply a thin layer of high temp gasket maker. Make sure the layer is thin enough for your upper thermostat housing to completely seat.

Reinstall the 10mm bolts and make sure to properly mount the rear metal bracket. Allow 15-20 minutes for the gasket maker to dry before starting your vehicle. Torque the 10mm bolts to specification and then reinstall the upper intercooler piping and PCV hose.

When you start your Mitsubishi Evolution, check for leaks and make sure everything is completely dry.

You now know how to replace your Evolution thermostat, and you’ve hopefully resolved your OBDII trouble code issues and have a rock solid temperature you can rely on.