Ive been having an issue lately. My coolant temp guage is usually at normal temp but often goes up to midway and 3/4 point. It went up to H just one time but i shut the car off as soon as i saw that, and after i started it back up the temp went down. The weather has been getting a little bit hotter lately (80-85 degrees), dont know if that would affect anything. Both fans seem to work. Running 50/50 coolant. I logged the coolant temp on evoscan and it showed me 195-210 degrees. But that shouldn't be enough to move the needle that much should it?

Im going to change out the thermostat in a few days, see if that changes anything. Any help would be greatly appreciated.

 

How's your coolant level? Try bleeding the cooling system. Maybe you have an air bubble somewhere.

 

Use a temp gun to see what actual temps are. Could be low on coolant, air in the system, bad temp sensor, or something else.

Next would be a bad ground. Make sure you have the IM to firewall ground. Also doesn't hurt to add more.

 

Coolant levels are fine. First thing I did after I noticed the issue was to take off the radiator cap and get all the air bubbles out. There were 2-3 air bubbles. But after I did that it seems like the issue only got worse. Now instead of the needle moving pretty fast it does the same thing but slower (goes up slowly, then drops slowly too). I didn't run the heater when getting air out of the system, probably should've done that.

 

try cleaning the contacts on the temp sensor. There are two of them on the thermostat, one for the ecu, one for the gauge.

 

The Evo has a very robust cooling system; remove a fan and it still works, run a half size radiator and it still works. I heard of a guy running with no fans. So, if the system is full of coolant you need to think outside of the usual.

If you haven't changed coolant recently there shouldn't be any bubbles in the system. Also, when purging the cooling system it doesn't matter whether the heater is on or not - there is no valve. If the engine is running coolant is flowing through the heater.

BTW, the gauge is not linear. It reads normal over a wide range of temperatures. If Evoscan continues to exhibit no abnormal temperatures suspect the intake manifold to firewall ground. If the reservoir suddenly fills to overflowing you have a blown head gasket.

 

Reconnect your ground wire from the chassis to the engine.

 

Thanks for all the help guys! Issue was resolved! Turns out the issue was that the ground wire from the intake manifold to firewall was a little loose. Tightened it down, took it for a 5 minute drive, and the temp didn't bounce at all! Took an Evoscan log of my brothers Evo just to be safe and his showed coolant temps of 195-206F. Thanks again!

 

This solved it for me too. Thanks for posting this.

What's this ground for btw? Temp sensor to that control the fan?

 

Ive had this same exact issue and it was in fact the ground wire. Be sure to check you wires too, mine started systematically melting wires one by one. Mine started with the exhaust cam angle sensor wire by the thermostat.