1991 pcm 351 temp gauge spike. PLEASE HELP

hello fellow nautique lovers. im writing today in hopes of gaining some understanding of a problem i am having with a 1991 ski nautique with a pcm 351. the boat was winterized by a professional at a shop this past fall and yesterday was the first day we went to drop it in the water. as soon as i turn the key, and before i even fire it up, the temp gauge spikes to 200+ completely maxed out as far to the right as it can go before the motor has even turned over while it is still cold. my first thought was the impellar which i checked and was fine. after i checked to make sure that was working and water was running through the engine i fired it up and it was good. i let it run for a while to see if it would get to hot and it didnt. temp gauge continued to stay spiked but boat ran with no noticeable problems, engine and exhaust felt normal and nothing was getting "too hot". the only thing done as of this year was a new distributor rotor and cap, which was also only hand timed which i also need to have done correctly with a gun. i dont think this would have anything to do with the temp gauge spiking while the boat is still cold though. any and all imput is appreciated. thanks.

This sounds like purely an electrical problem.

Basically, the temp gauge is just an Ohmmeter, and what you are actually reading is how much resistance there is to ground.

Now the sender, that is what is reading the temperature, and what it does is increase or decrease resistance to ground, depending on temperature.

The fact that the temp gauge spikes as soon as you turn the key, means that your sender wire is finding a direct path to ground somehow.

I would suspect that it (the sender wire) somehow got pinched against the block when the new distributor was being installed. Either that or it was accidentally pulled off the sender and hastily reattached to the nearest nut or bolt. Either of which would ground it out.