I've never had an impeller go out causing the engine to heat. I've opened it one time and there were 2 blades on it. I found all the others mashed on the intake side of the oil cooler.

We had a situation of a really bad raw water seal leak motor sailing and beating into confused 6' seas and 30 knots near the nose on the way to Bocas Del Toro. I kept resetting the bilge pump counter every 30 minutes to see if it was getting worse (it was cycling about 30 times every 30 minutes) The engine kept it's 185deg. and I was not looking to swap it with the spare while profusely sweating and throwing up so we just kept going for 9 more hours. Made it to the Bocas marina and a slip where I swapped it with the air conditioner running the next day (much better). There was dry salt 1/4 of an inch thick on the side of the engine when we got there.

I've got to cinch down 3 hose clamps around a new impeller in order to get it in. If I don't it's impossible to install.