I had my 1991 7.3L F-250 4X4 detailed yesterday. The engine was cleaned. Went for a drive last night, the red engine light came on immediately, and the Water temp gauge was pegged full Hot from the time I started it. The engine is definitely not overheating, runs great, blah, blah, blah. Any ideas on where to start? Where is the sending unit/units for water temp. Thanks.

 

sounds like ur temp sensor is grounding or shorting out doo to the moisture u may have all ready guessed that thou im not sure where the sensor is but gona take a guess and say its on the intake manifold id just pull the plug off and blow the water out with blow gun and try that

 

Its actually your temp switch that runs the gauge.... On small blocks is on the driverside front of the intake manifold... I know that doesn't help but its a start. It only has one lead coming from it.

 

Yes, the engine light comes on to alert you to the "overheating" condition. As the others have said, your temp sender wire is shorted to ground somewhere between the dash and the sender in the engine. Don't let it go too long like this, otherwise the gauge itself could be damaged.

 

Much thanks to everyone. I got home from work today and the truck is back to normal. I guess it was just wet. Thanks again for your responses.

 

You still have a problem in a damaged wire somewhere. You should at least find the temp sender and hand over hand trace the wiring back to the firewall. You might find a wire bundle that has rubbed through on something. This could leave you walking someday.