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!

 

Defenently sounds like a ground, I have the same problem in my camper, witch only happens on really hot days, working it hard, mostly in hills. All 4 gauges crap out though for a moment, then come back to normal.

Here is the 2 sensors, one for the light, one for the gauge it's self. You can use either one to plug in a real gauge on it. I did this in my camper using the one of the side, the Temp Light Switch as I still wanted all my dash gauge to work.

Front drivers side of engine.

 

I think its the relay in the dash when my gauges peg i just rap the dash and they all go back to "normal". Another thought maybe it could it be the theromstat sticking if its not the right one.

 

watch it with that red coolant in there. these trucks are supposed to run green.
i have had the pleasure to get 6 vehicles in over the past 2 years for hot run/overheat problems, and everyone was fixed by doing nothing more than dumping the red coolant and putting the green back in it.

 

thanks for the replies! I really appreciate the pix. I forgot to mention in the first post that I have a screwy fuel gauge too (dual tanks, doesnt seem to read accurate on either), and there's an electrical gremlin in the tach when I turn on the headlights (at idle it reads 0 rpm). I'm pretty sure either there is a bad connection/ground somewhere or someone messed with the wiring at some point and crosswired something. Going to check the sensors today and see what's up.

As far as the red coolant, I'll keep a close eye on it. I dont drive the truck right now because my utlility bed isnt tied into the frame and I need to do rear brake work. I've been having trouble finding "diesel" coolant, and came across this stuff at Tractor Supply. It says its supposed to work with everything and is specifically made for diesels, but if I can find some green stuff (dealer I guess) I'll flush and swap it out before I drive it regularly.