Ok guys, here's the scoop. On the '89 dually (7.3, NA, C6) the last few days, I run it a while, temp is fine. Shut it off for a few minutes, restart it, and temp gauge shoots all the way to hot. The engine light also comes on. Each time I've then drove it for 3-4 miles to get back home, gauge stays all the way up.

Get back home, pop the hood, top of rad and top hose are hot, but not too hot to touch, bottom hose is warm. Rad is full, first time overflow tank was low, but not quite empty, topped it up and happened again second time.

I'm leaning to one of two things. Either the thermostat is starting to puke and it's not opening fully, or some sort of electrical issue. I seem to keep thinking that the one sending unit was strictly a 'too hot' type switch, I'm wondering if there is something going on with that switch or circuit?

I have a new stat and gasket coming in to the local IH dealer today, as the crewcab needs one anyway.....would rather not throw it in the dually unless I really need to, as it's getting retired later this winter anyway.

 

on the driver side head (i think) is the temp sender for the gauge. it is most likely bad.
whenever i pressure wash my engine water gets in the sender and shorts it out, then the gauge shows overheat and the CEL comes on for 2-3 days till it dries out.
.

 

Mark you really need some real gauges


x2 on wiring problem.

 

It's been pretty wet here the last few days, we've been getting a lot of rain. I'll have to hunt up that pic of which one is the sending unit, I can never remember.....wonder if I can thread it out, and another back in quick enough to not lose too much antifreeze......?

John, lots of things I need, but when I need to do the same for 3-4 trucks, it just isn't in the budget anymore!

 

I do believe this will answer your question

 

i picked this little sucker up.removes all guesses.sure is some handy.
Amazon.com: HDE Temperature Gun Infrared Thermometer w/ Laser Sight: Home Improvement

best part for you;
it can often be used for all 3-4 trucks.

it helped me correct my temp gauge.she was reading 15 degrees too high (didn't know until i got the tool,but i suspected.that's why i got it.) so that's when i did a little researching,and often digital temp gauges require a devoted ground (i had all 3 shared) once i ran a devoted ground,i see my gauge read what this point and shoot tool reads.right around 195-205 degrees normally,under no load.
one of the best 20 bucks (less) iv ever spent right there.