Somebody enlighten me here,I am running a stage II Procharger on a 96 502 EFI with no thermostat,side water pickup on bravo1 and water pressure is 5 lbs at wot.Heres my problem, the water temp jumps from 110 to 150 like a thermostat is opening or closing!Yesterday it stayed just under 150 all day.Do you think my sender or gauge is bad or could it be the impeller in the seawater pump?By the way it did the same thing before I intalled the Procharger. the impeller and housing on the seawater pump were replaced a little over a year ago and the problem appeared not too long after that,I figured it was the thermostat then but t ruled that out that since I no longer have one.HELP!

My guess is first the impellor has gone/going south on you. Next problem is when the implellor starts falling apart parts of the impellor go down stream of the water pump. When parts get to a cooler the small holes in the cooler keep the part from getting past. Only problem is it also stops the water from getting past. Thus the high engine temp. Everytime I see water temp go any higher that want I am use to seeing I replace impellor & start hunting down all of the parts.

I have helped many out on lake who were having overheating problems after just having replacing the impellor. I start taking hoses apart & pulling out impellor parts.

I always carry a spare impellor.

Indy's right, everytime an impellor has shredded, I find pieces in the housing & hoses. In my Procharged HP454, only my oil temp would get that high! My normal temp on a really hot day was barely on the gauge! You have an obstruction somewhere.
Good luck!