Impeller?

hello friends ! I have a searay sorrento 24 cuddy cabin, 5.7 engine which i a bravo drive, The difference ? Alpha drives have the water pump impeller internally with the stern drive. those can set while in storage.
the bravo drives have a water pump in front of the engine just like most american V-8 engines. I have experianced a over heating problem in the past. I started my detective work by checking for water flow. I replaced the hose that comes off the stern drive and connected the drive with a muff to verify water reaching the water pump.( not for the novice-12 beers) still ran hot. Next pulled the water pump and checked the impeller. All was good andpump is only about a year old. I also removed the bellows at the drive looking for any pieces of flapper valve. I found a half, so removed the upper exhaust bellows ( both sides) ( 3 beers and 2 bandaids ) and installed 2 new flapper assemblies. Some owners say the flappers arent necessary, but engine ran fine with them,soooo
next up was old school.....pull the thermostat and test it in hot water, ( rated to open at 140 F) tested 3 times and #1 opened, #2 stuck, #3 opened. So then i decided to run the engine without the thermostat.
Guess what still ran hot ( according to my gauge ) NOW im wondering whats up ? shouldnt run hot without a "stat" So replaced both the sending unit for engine temp as well as hi temp alarm. Cranked it up and after about 5 mins at idle the gauge still creeped up to hot ( about 200 F) what gun, ? OKAY.....Just like getting a second opinion from a doctor i had to keep the detective work going. Parts replaced, pump is pumping, new hoses, new sending unit, no obstructions, huuuummmm. I broke out my digital infared thermometer ( harbor frieght $20) Ran the engine from cold start up, guage creeped up to hot again...BUT, USING the thermal gun, scanned the intake cooling hose, and the thermostat housing and the outlet to the exhaust and everything was in normal limits...so my diagnosis was maybe the gauge. U-TUBE videos say you can pull the sending unit wire and ground it to the engine and the gauge should max out. IT DID ! So i believe the fault lies in either the wiring to the gage, OR the sending unit(s) are possibly for a different engine. Take note...when replacing the thermostate, use OEM type gaskets, look closely and you will see they have small metal brass pins that maintain the ground, so dont use any RTV and accidentally cover them up. Now i didnt replace parts just for the exercise, the boat is a 1988, so this was normal preventive maintence. the Biggest reveal on this project was the thermal thermometer, . And as side bar, wiring can build up resistance over the years and you can't tell because its insulated. the sending unit can be tested with a OHM meter both hot and cold....so theres my story. hopefully one of my procedures is something you may have overlooked and will help eliminate what could be causing your problem........Sincerely James
 
Replacing the impeller is fairly easy, just have some patience. Follow the advice from the above posts, lots of good advice there. One additional tip : take a picture of the serpentine belt on the pulleys before removing it, that way you'll know how it goes back on.
 
Lol! Pictures before I remove a thing has been my best lesson. I take pics every step of the way on most jobs I’m doing for the first time. Boy has it saved me. After 3-4 beers I barely remember my name.
 
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