As of last night, when i'm driving, the water temp gauge would do some crazy things where it would get almpost to the H, then go back down to where it would normally be. And it would do this back and forth until i got to where i'm going.

What would be causing this? There are no visible leaks. I got my car back from having a clutch installed on friday and this didn't start happening til last night after i left work. But i can't think of anything they would have had to mess with regarding the radiator while swapping out clutches. I'm at a loss. The rad is full of fluid too.

 

That happend to me wend I lift the head I hope that's not you problem

 

I can't forsee it being that. I haven't hit more than 8psi in my car in over a month due to the slipping clutch. And it idles normal.

 

thermostat

 

I would verify the actual temps of your coolant. You can get a IR temp gun and point it at your radiator and radiator hoses to give you a rough idea if your actually overheating. Ive done this before and got decently accurate readings, good enough to diagnose coolant system issues anyhow. ANother option is using a scan tool you can actually read the temps of your vehicle.

I suspect its the temp sensor for the gauge, or the gauge itself acting screwy. Make sure the sensor is ok (should be some ohm resistance specs somewhere) and the wiring isnt damaged and grounding on somewhere.

The important thing to find out is what actually is the coolant temp vs what that guage is doing.

 

Run a log on the car and see what the coolant temp is reading is that possible? Also I would just change the t stat and gasket it's 25$ from mitsu and it is simple to try anyways! And plus you could do a coolant flush as well just to make everything fresh! Hope it isn't a big deal!

 

I know DSMs had both a gauge and ECU temp sender, I don't remember if the Evos do or not (I didn't pay attention the last time I had the housing off to be brutally honest). If they have two sensors you can log the coolant temp and see if it's actually fluctuating or if the gauge sensor's just whack.

Otherwise if you have access to a heat gun that method works fine too.

 

if your car is overheating usually when you stop the car and look at the overflow it should be boiling or very hot. to verify.

 

They do

 

I know. None of those things happened. Probably thermostat

 

The sensor (single wire) at the thermostat is sending a signal to the dash and is not getting a good ground. It shoots up when your fan comes on.

Make sure the ground to the intake manifold is in place, or do a DIY from the battery to the sensor ground. I know...old thread.