1975 20hp Merc

[Ford8n]

I have a 1975 Mercury 200 20hp long shaft tiller. Last spring we replaced the impeller on it. I believe we took it out 2 times and it quit pumping water on the river. It got hot. Checked compression and its 100/110 in the 2 cylinders. Fast forward to now...dropped the lower unit and the impeller is good yet. Looks brand new. Checked the tell tale tube and its not blocked. Why wouldn't it be pumping water? there is no obstruction anywhere that I can tell. I also need to rebuild the carb again.

 

[oldman570]

Re: 1975 20hp Merc

Parts of the old impeller could be blocking the water flow up in the motor, or the water tube from the pump to the block might not be in the grommets as needed or the grommets need to be replaced. Best to drop the LU and clamp the hose on the water tube and the motor to make sure that the water flows good thru that part of the cooling system and there are no blockages. Then repair as needed. JMO
Oldman570

 

[Ford8n]

Re: 1975 20hp Merc

Parts of the old impeller could be blocking the water flow up in the motor, or the water tube from the pump to the block might not be in the grommets as needed or the grommets need to be replaced. Best to drop the LU and clamp the hose on the water tube and the motor to make sure that the water flows good thru that part of the cooling system and there are no blockages. Then repair as needed. JMO
Oldman570

I'll check that out. I do believe the grommets are in poor shape atleast the lower one is. Neither impeller was missing any pieces or damaged in anyway. I'll hook up the hose and see if I can get water through. Any chance the copper tube cracked?

 

[imported_bowfisher]

Re: 1975 20hp Merc

I have seen the brass sleeve inside the rubber impeller spin on occasion, might be something to consider also.
That said I would be really suspect of pieces of the old impeller plugging the powerhead, see that alot with the older Merc motors.