Impellor Replacement - 4.3L Merc

bigdog · 01-14-2008, 10:41 PM

I am way overdue in changing my impellor on my Mercruiser 4.3L.
Would like to do this myself in the Spring, when getting the boat ready before
the first launch.

I am fairly mechanical, is this a easy DIY replacement for a back-yard mechanic ?

Not really sure where the impellor is located, but I suspect part of a hose
connection to the engine. I suspect that if I am removing a hose connection, new gaskets should be used when re-assembling.

Any help would be greatly appreciated.

Thanks.
Bigdog

jrc · 01-17-2008, 08:06 AM

What kind of outdrive do you have? I'm pretty sure that on all Bravo drives, the sea water pump is on the engine and run by a belt. On Alpha drives the impellor is inside the outdrive. I watched the mechanic do it on my first boat's Bravo 3. Other than getting to the pump, it's an easy job.

But you may want to wait for someone who has done it himself to chime in. Plus you may want to ask/search some of the pure boating forums.

Dave R · 01-17-2008, 11:42 AM

I'm 99% sure you have an alpha drive based on previous threads. It's not a difficult job to change the impeller on an Alpha, and it's certainly a DIY project. There's a common misconception that having the pump in the drive leg versus on the engine (like a Bravo) makes the job really complicated. It's not true, IMO (I've replaced both Alpha and Bravos impellers).

Here's a link to the procedure: http://www.mercstuff.com/waterpumpinst.htm

eye spy · 01-17-2008, 02:18 PM

I needed new imp. last year took it over to guy on 106 with shrink wrap boat out front of house. He replace imp, lower unit oil, service drive, and installed new gasket on drive. Just over 100.00 bucks for everything. His phone is 603-267-7223 charges 50 per hour for work 1/2 cost of lake Winn dealers.

MV1 · 01-19-2008, 11:55 AM

Remember, there are two main Alpha Models out there. Alpha I-R which uses plastic pump housing and a "Stiff Vane" impeller which should be replaced every 2-3 yrs. This drive was used till 1991. Then there is the Alpha I-MR which is still used. This drive has a completly different pump with a metal housing and a "Flopy Vein" impeller. Some manuals list this as a lifetime impeller but still should be checked whenever drive is dissembled for any reason...either way you still should have a service manual of some kind before doing work.

MV1 · 01-19-2008, 01:25 PM

Sorry, need to correct my last post. Both Alpha I-R & MR use stiff impeller and Alpha Gen-II use the metal cover, flopy vane pump.

01-14-2008, 10:41 PM	#1
bigdog Senior Member Join Date: Apr 2006 Location: Central MA-Gilford Posts: 1,411 Thanks: 308 Thanked 117 Times in 94 Posts	Impellor Replacement - 4.3L Merc I am way overdue in changing my impellor on my Mercruiser 4.3L. Would like to do this myself in the Spring, when getting the boat ready before the first launch. I am fairly mechanical, is this a easy DIY replacement for a back-yard mechanic ? Not really sure where the impellor is located, but I suspect part of a hose connection to the engine. I suspect that if I am removing a hose connection, new gaskets should be used when re-assembling. Any help would be greatly appreciated. Thanks. Bigdog

01-17-2008, 02:18 PM	#4
eye spy Junior Member Join Date: Dec 2006 Posts: 15 Thanks: 0 Thanked 0 Times in 0 Posts	boat I needed new imp. last year took it over to guy on 106 with shrink wrap boat out front of house. He replace imp, lower unit oil, service drive, and installed new gasket on drive. Just over 100.00 bucks for everything. His phone is 603-267-7223 charges 50 per hour for work 1/2 cost of lake Winn dealers.

01-17-2008, 08:06 AM	#2
jrc Senior Member Join Date: Apr 2004 Location: NH Posts: 2,689 Thanks: 33 Thanked 439 Times in 249 Posts	What kind of outdrive do you have? I'm pretty sure that on all Bravo drives, the sea water pump is on the engine and run by a belt. On Alpha drives the impellor is inside the outdrive. I watched the mechanic do it on my first boat's Bravo 3. Other than getting to the pump, it's an easy job. But you may want to wait for someone who has done it himself to chime in. Plus you may want to ask/search some of the pure boating forums.

01-17-2008, 11:42 AM	#3
Dave R Senior Member Join Date: Jul 2004 Posts: 2,974 Thanks: 246 Thanked 736 Times in 438 Posts	I'm 99% sure you have an alpha drive based on previous threads. It's not a difficult job to change the impeller on an Alpha, and it's certainly a DIY project. There's a common misconception that having the pump in the drive leg versus on the engine (like a Bravo) makes the job really complicated. It's not true, IMO (I've replaced both Alpha and Bravos impellers). Here's a link to the procedure: http://www.mercstuff.com/waterpumpinst.htm

01-19-2008, 11:55 AM	#5
MV1 Member Join Date: Jan 2008 Location: Meredith Posts: 25 Thanks: 0 Thanked 4 Times in 3 Posts	Remember, there are two main Alpha Models out there. Alpha I-R which uses plastic pump housing and a "Stiff Vane" impeller which should be replaced every 2-3 yrs. This drive was used till 1991. Then there is the Alpha I-MR which is still used. This drive has a completly different pump with a metal housing and a "Flopy Vein" impeller. Some manuals list this as a lifetime impeller but still should be checked whenever drive is dissembled for any reason...either way you still should have a service manual of some kind before doing work.

01-19-2008, 01:25 PM	#6
MV1 Member Join Date: Jan 2008 Location: Meredith Posts: 25 Thanks: 0 Thanked 4 Times in 3 Posts	Sorry, need to correct my last post. Both Alpha I-R & MR use stiff impeller and Alpha Gen-II use the metal cover, flopy vane pump.