Cooling problem Mitsubishi Evo 4

[Carlos]

Hello!

A friend imported an Evo 4 a few months ago, but now it's starting to overheat. Or is it?

The problem is, everytime he stops, the heatmeter goes up, 15 to 30 degrees, it actually won't stop rising sometimes. But! If you rev to 2500rpm quickly, or just full throttle, it cools down to normal within a second. This also happpens when I turn off the car when it's overheating, turn the ignition back on and it's cool again.

What is causing this?

The car is stock except for the manifold.

 

[Ibonibo]

Take a voltmeter and check the sensor, it is probably the sensor that is broken, if it goes back to normal in a second that is not normal, so that is my best guess.

 

[Nicktune]

Sounds like the thermostat is not working properly…
From the evo 4 workshop manual..

Inspection
Thermostat check

(1) Immerse the thermostat in water,and heat the water while stirring. Check the thermostat valve opening temperature.
Standard value : 76.5 +_ 1.5 C

(2) Check that the amount of valve lift is at the standard value when the water is at the full-opening temperature.
Standard value :

Full-opening temperature :90 C​

Amount of valve lift : 8.5mm or more​

NOTE
Measure the valve height when the thermostat is fully closed, calculate the valve lift by subtracting this measurement from the valve height when the thermostat is fully open.

THERMOSTAT KIT part# MD345617 should cost around 40$

 

[SRV2LOW4ME]

Remove the front bumper and check the rad for dents and clogged fins.

I've seen this problem before, and after removing the bumper and blowing air or water through the rad to remove all the debris, and then taking a small flat head screw driver to open up all the dented fins on the rad, the problem went away and the car ran far cooler than before.

 

[Blaze_409]

If not that then maybe he is running too lean fuel-air mixture