Yesterday My '93 5.0 started to overheat almost 5 minutes after being put in the water. I shut it down before it hit 200 degrees, and put it on the trailer and went home. Today, I took the impeller off, and found it was burnt up ( see pic ) I backflushed the system from the engine compartment (where the sterndrive feeds the thermostat housing). The water flowed perfectly fine back out to the impeller housing. I hooked up the muffs and water flowed fine into the impeller housing. The exhaust manifolds each flowed well too. So, I gather there is no restriction. I put on a new impeller, hooked up the muffs, and water still didn't flow to the thermostat, even when turning the engine over. If I started the engine, and gave it a rev or two, water would start to flow very well and remain that way. Its like the impeller lost its "prime" or something. So i hooked the sterndrive feed upto the thermostat housing again, and if I let it idle long enough, water would stop gushing and start to trickle out the bellows, and the engine temp would climb. I would give it a rev, the bellows would gush water for a while, and the temp would fall to 150 again. Sit for another 3 mins in idle, the bellows would stop gushing, and start to trickle, engine temp would climb, and a good rev would fix it again. It seems like the impeller is loosing a prime. Any Ideas?<br /><br />BTW, the impeller in the picture was replaced last year too.
