Mecruiser Alpha One impeller

[Sir Reel]

I have a Mercruiser 4.3L MPI with fresh water cooling. It has a separate fresh water pump and pickup on the engine but I have heard that you still have to change the impeller in the Alpha leg. Cools the gear box or something?
Does anyone know if that is the case? I have about 300 hours on it and have had no problems.

Thanks!
Dave

 

[Gypseas]

The sea water pump in the leg most likely pushes water through the heat exchanger cooling the fresh water/glycol circuit. Fresh water pump circulates water through the motor.
hope this helps

 

[Gypseas]

http://www.boatfix.com/merc/Servmanl/6/6B3R3.PDF

some good reading

 

[Sir Reel]

Hi Gypseas, Thanks for the leg manual. My motor has a separate brass water pump on the front of the motor with a separate through hull seawater pickup. There is a hose coming from the leg but it has been cut and does not supply water to the motor. Just tryting to find out if I need to replace that leg impeller for any other reason.

 

[combover]

if the hose that comes from the transom shield is cut and plugged that means the impeller mounted on top of the gearcase (inside the drive) is no longer needed. the raw water pump mounted on the front of you engine now supplies the cooling water to the heat exchanger and exhaust manifolds or risers depending on the cooling setup.

the impeller does not need to be replaced in the drive it doesn't cool the drive and it probably has been removed if the job was done by a pro the housing would be there just no pump.

side note the hose from the transom shield that supplied water if plugged should be plugged with a dowel and TWO hose clamps
hope that helps

 

[Sir Reel]

Thanks Combover, I think that answers my question and I don't haev to wrroy about it now!
It was a factory install so should be done as you suggested.
Cheers!