Water temp Gauge/Sender Issue
 

Having a dillema with water temp gauges. Both sides will read no temp while running. Stop, shut down, turn off, and then turn keys on and they read temp. Start and get underway and they drop back to nothing. Doubly frustrating because I just switched from a straight crossover to a thermostat one. Seems to be running proper temp, but its a PITA not being able to see what temp is at while running. Any ideas, I am kind of stumped on this one.

Are you running a thermostat?

I have a similar situation. Gage will work only when engine is off and warm. I think in my case, the thermostat isnt opening and cool water from the raw water pump is circulating across the thermocouple. New TStat going to be installed tonite.

If not thermostat, maybe relocate the thermocouple (sorry, didnt see you were running a cross-over).

Running crossovers with a t-stat, but the senders are in the intake manifold so they should not have any cold flow across them.

Sounds like a ground issue on the motor. Check to see if you have any voltage at the sending unit when the engines are running, check between the sending unit and battery first then check between the sending unit and block.

I will check. If it is a ground why does it only not read while running?

When the motor is running the voltage potential of the engine can increase to a point that affects the gauge.