Do you have evoscan? If so remove the coolant sensor, place it in a pot of boiling water (with it still hooked up to your car) and see what evoscan is reading. You should read 212deg.

 

No, I don't have evoscan.

 

was u able to findthe problem cause my buddy is havin the same issues he changed tstat and the two sensors and still runnin cold wtf .

 

Did you guys figure out the problem? I am having a similar issue....
When I satrt the engine it idles at 1500-1700 rpm for a while then drops to around 1200 rpm. The temp gauge stays just above cold until I have driven for a good 20 minutes. When I put the car in nuetral and coast the idle goes up to 1500 rpm again. My CEL is on, and the code is for "not reaching operating temperature within designated time", which I think is 11 minutes. The fan is not on, and the upper hose has pressure, which leads me to believe the thermostat is closed. Any ideas?

 

Having this issue right now after installing a brand new thermostat case and OEM thermostat.

I was replacing Mishimoto race thermostat. Car has had a Mishi rad in it since 2013. Fan operation seems normal and upper hose has pressure.

Isn’t there 2 coolant temperature sensors in the housing? I assume one is for the ECU and one for the gauge.

I’ll dig into it more tomorrow. Feeling like it’s the sensor and/or the wiring, unless the fan control module is acting stupid whilst driving and you can’t tell.