I noticed my apexi el2 water temp reading is always 5-8 degrees cooler than the reading from the power fc.

Which one is more accurate? Here is where i mounted the sensor for water temp gauge:

 

Hopefully someone will chime in that knows more than I but I also have mine located there; I think the factory gauge's sensor is mounted on one of the irons so there should be a temperature difference. If I remember right that is about the same difference i have between the two sensors.

Not sure how accurate this is but just found this "The level sensor is in the top of the radiator. The sensor for the gauge is the little one in the rear iron. The sensor for the ECU is in the back of the waterpump. "

 

^ that is correct

 

I believe the PFC gets it's readings from the OEM sensor behind the waterpump housing. My aftermarket gauge sensor is taken from the (former) TB coolant line hose and both generally agree within about 1 deg. C. ??

 

I think the difference in temperature shouldn't make much difference. But the ecu working on that information.

 

well, the water temp is important to me since i need to know when to pit in when it gets hot. I have been following the ECU but was just pretty surprise to find out that the temp varies up to 8 degrees...and to me, there is a big difference between 108 and 116!

 

I'd change the stock gauge for a new one and rely on it + PFC.

 

To me, the filler neck is a very poor choice for a water temp sensor. There really isn't any flow of coolant there. The sensor should be in a place where the coolant circulates.

 

I think there are a good flow of coolant going through the filler neck but where would you recommend?