I have a 1989 F350 with a 7.3 IDI and thought I was having an overheat issue. My radiator was only about half full and I was getting a redline reading on my dash coolant temp gauge (along with the "ENGINE" light). I just flushed the radiator and added new coolant and ran the engine again only to get a sporadic temp reading and engine light.

The gauge looks as if maybe its getting a bad ground or something, because it went from the line at "C" and jumped to "H", then past (hotter) "H" and flickered back and forth. The whole time the coolant in the radiator was only warm, as was the upper hose, and I'm pretty sure the thermostat opened since the new coolant was red and the old coolant in the block and heater core that I couldnt flush out was green, and now I'm left with a murky gray green color in there.

Sorry to be so long winded but here's my main question...where can I find the temp sensor for the gauge cluster on this engine? I'm new to diesels so I'm not 100% sure what's what on here yet. I suspect its either a bad sensor or bad connection/connector. Has anyone else had this problem? Probably most importantly here is does the "ENGINE" light illuminate based off the gauge sensor or is there a second one just for the light/computer?

Any help here is appreciated, thanks!