1997 Mercury Force overheating

[BTruaxJr]

New water pump kit, thermostat, heat sensor... boat over heats 200' from launch!!! Dropped lower unit and rigged up a hose to tube from pump, ran boat at idle 15 min and 3-4000 rpms for 15 min... no problem, engine was so cold there was condensation on it and water out pee hole was 35-40 degrees. Im thinkin its in the lower unit, could I have bought wrong water pump kit? Everything Ive read says Mercury put the lower units from the 40 hp on the 75s but I have a 40 hp lower unit from the original motor on this boat and its obviously smaller...the driveshaft alone is 5/8" vs 3/4". Do I have some kind of "Frankinmotor"???

 

[Texasmark]

Did you put the key in the drive shaft and then slid the impeller down on the water pump mounting plate? No key, no turn the impeller when the engine runs. Knowing that the water pump is eccentric/slightly oval, rather than perfectly round and to get the impeller installed, the tips have to be folded back, did the impeller seem to fit snugly in the space allowed in the pump....top to bottom and blades bent back significantly on one side and slightly on the other?

If all that checks out, did you stab the water tube into the hole in the bottom of the engine block? Did you replace any seals associated with that stabbing operation, or at the outlet of the water pump to the copper tube?

 

[BTruaxJr]

OK, found another pump kit and installed it making sure pump outlet and tube went together correctly. Tested in a barrel of water and it seemed to pump a good volume... Took boat out yesterday and ran it all day, even let it idle once for 15 min after running it WOT. Buzzer never came on and water out pee hole was barely warm. Thanks for the help guys. BT

 

[nalegtx149]

same thing happened to me years back with a Merc 25. Off by 1 number on the part....i always go OEM through a factory parts diagram for parts such as this. glad it worked out for you!