Flakey Temp Sensor?
 

New rebuild with block thoroughly poked, prodded, boiled and cleaned; new Champion aluminum radiator rated at 500 hp; 4 lb pressure cap; timing advanced one scribe mark from center; new tested 180 degree thermostats, fixed in place; runs great. But, ...

Immediately upon start up the temp gauge goes straight to the hot peg, then comes back to read correctly as the engine temperature comes up. I bypassed the left head overheat switch to be sure that was not the problem. Driving even in very hot conditions, the temp gauge stays about 1/8" above center, which seems about right for 180 degree thermostats. But idle for any time, even in mild temperatures, the gauge climbs right to the peg. But no boiling, spitting or steam from the overflow, even if I let it idle at hot for an extended time. The head water outlet reads about 195 degrees and the radiator under the top hoses reads about 185, so the problem is the sensor.

This is the second new temp sensor. The first just went full hot and stayed there. I think this one is also faulty and goes open circuit when the temp goes up to 190 or so.

My question is, where do I get reliable water temp sensor?

Re: Flakey Temp Sensor?
 

Are you using one or two senders? There were originally two, one was a temperature sensor and the other was an on/off switch. Any open causes a full hot gauge reading which is what happens with the on/off switch.

Re: Flakey Temp Sensor?
 

I to take the left cylinder on/off switch out of the trouble-shooting, I bypassed by simply connecting the wire from the gauge and the wire from the right head (the temp sensor) together.

I have pretty well concluded that the temp sensor is malfunctioning. It goes open circuit and runs the gauge full hot at any temperature 190 or over.

My question is, who sells a reliable temp sensor.

Re: Flakey Temp Sensor?
 

Yep, missed that line!

Ford sold reliable senders if you can find NOS. I would guess that the temp sender is the same issue as other early Ford replacement senders, an attempt to use a different tech than the original K-S senders and not totally compatible with the gauge.