Closed Cooling System & Impeller in Lower Unit

[chriscor]

Being a Newbie, just trying to better understand my motor/drive configuration:

My boat is equipped with a 2005 Mercruiser 4.3 L MPI with an Alpha One Gen II drive attached to it. It is a closed cooling system on board
getting it's raw water from a through hull water inlet. The seawater pump is attached to the starboard side of the motor. As far as I can see, water intake from sterndrive unit has been blocked. So far so good.

I was wondering what is the role of the impeller in the lower unit of my Alpha sterndrive? Might it be idle? If not - and I have learned from some tech. specs - how is it cooling the drive which is below water anyway? And, finally, should the impeller be changed from time to time? Even it might be idle or is for "drive cooling, only".

Thank you for sharing some thoughts on this.

Sorry for my bad english

Best, Christian
Hamburg, Germany

 

[Don S]

Re: Closed Cooling System & Impeller in Lower Unit

EDIT: Missed the part about thru-hull fitting :redface:

The raw water pump in the outdrive provides cooling water for cooling of the drive only.

 

[cr2k]

Re: Closed Cooling System & Impeller in Lower Unit

Reckomended replacement is every other year. Maybe not quite as important in your case but should be on a regular basis. If used it wears. If not used it sits and dries out and the blades take a set and are not effective.
While the lower drive is in the water the upper (and less of the lower at plane) is not. There are gears and oil in the upper also.

 

[chriscor]

Thank you for your prompt answers.

Merry Christmas!