So I've got a 96 Legacy wagon with 140k on the EJ22.

 

Got a little runnability issue that is being discussed elsewhere, but thought I'd ask here about another issue.

 

My temp gauge in the dash rarely comes up off the needle at cold. The T-stat is a brand new OEM unit, water pump is brand new, the fans come on, and I have burped the system a couple of times just to be sure.

 

Heat/Defrost works AWESOME

 

Would a bad coolant temp sensor default the fans to constantly on? And if so, why would I occasionally get slight movement of the gauge when sitting for a while?

You have two temp sensors on the engine. One is for the ECU, which also runs the fans. The other is for the gauge in the dash. The gauge sensor only has one wire.

The way these work is pretty simple, as temperature goes up, resistance of the sensor goes down. Cold = high resistance, hot = low resistance.

If the gauge always shows cold that could mean the sensor is bad or there is high resistance between the gauge and sensor. The simple test is to remove the wire from the sensor and ground it. The temp needle should peg hot. If there is a bunch of corrosion on the spade terminal on the sensor that will cause the high resistance which keeps the needle low. Clean it off and cover it with dielectric grease.

my buddy has a 95 that the fan runs constantly and she is a hard start when cold. this is compounded by being a franken motor, although it runs fine when warm. I told him to replace the engine temp sensor.

 

This will be the one with the brown plug under the intake. the other single spade terminal is for the gauge. The brown one is for the ECU

if temp senser is failed the fans will default to on more likly a coolant circulation problem or still air in coolant did the rad get hot ? very rare to see and bad sensor but very commen to see coolant problems is the waterpump turning

Where under the intake is the second temp sensor?

They're right next to each other pretty much straight down under the idle control valve.