I recently bought a 9 year old BF45, and I've noticed the cooling water telltale (pee hole) getting blocked regularly, and the flow is weak even when it's not blocked. I took off the thermostat, and found a lot of small rubber fragments around it, which I assume are bits of the impeller blades. I guess these guys are also responsible for blocking the pee hole. I'm obviously going to replace the impeller, but my question is how do I go about clearing the impeller bits out of the passages in the water jacket? Should they come out if I reverse-flush the engine (through the pee hole nipple) with the thermostat cover removed, or do I have to put some kind of acid through the system to melt them? <br /><br />I was thinking maybe I could train a cockroach to crawl through and eat them