View Full Version : Impeller on 3.3 Mercury outdrive

Tough Life
01-11-2007, 08:47 AM
Good Day All,

Forgive my ignorance on this topic but is it a fair statement to say that the impeller on most outboards is located in the lower unit? I have a 3.3 Mercury 2 stroke for my dinghy that's not pushing water so I'd like to check the impeller. I've misplaced the manual so before I start taking it apart I'd like to know that I'm looking in the right place. Any help is appreciated, thanks.


01-11-2007, 03:22 PM
usually situated just behind the prop on small 2-strokes

Remove prop
Remove outer plate of water pump
Remove impeller
Check impeller for wear & get new one if worn
Take opportunity to clean out impeller housing
Replace outer water pump plate

Tough Life
01-12-2007, 10:26 AM
Thanks. I'll take a look.

01-13-2007, 05:51 PM
Hi Lads,
I have never seen a water pump in the gear housing behind the prop. If the water pick up holes are above the gear housing, the impeller is above that. Usually the leg / casing splits in half and the water pump is located in the lower half. The power shaft from the block runs down through the water pump to the gear casing. If this is not the case I will be surprised but then again it's a sad day when you don't learn something.

01-14-2007, 08:35 AM
Here is a picture how it is on the 3,9 to 9,8 hp 2 stroke engines.
Nr. 8 is the impeller.

But I thought on this smaller 3,3 hp (older) 2 stroke that there is a outer pump plate situated right above the prop.
When you remove this you see the impeller.

Let us know Doug.

01-14-2007, 08:58 AM

it should be the same as in the diagram. If the 3.3 has a fwd, N and Reverse it should have two shafts; one is the power shaft that the impeller runs on and the other is the shift shaft.

Tough Life
01-14-2007, 09:23 AM
Good Day,

I removed the prop and the plate behind it but Dave is right, it is the gear housing and only gear oil is behind the plate.

So I removed the two bolts that attach the lower unit but the lower unit doesn't want to come off. It appears to still be attached to something coming down the shaft of the outdrive, however I can't determine what it is attached to.

I need to find my manual (haven't found one online yet). When I figure this thing out I'll be sure to post an answer. Thanks for the replies so far.


Tough Life
01-14-2007, 01:48 PM
A little more information .....

I finally found a picture of the gear housing for the 3.3 and it is pretty similar to the one posted by PMvdb395DA. The impeller is located in the water pump housing that sits on top of the lower unit.

There is a rubber cap on the left side of the motor just above the lower unit that when removed you can see the drive shaft, gear linkage, water tube and the top of the pump housing. The drive shaft and the water tube are connected to the top of the pump housing. When I remove the two bolts that secure the lower unit and gently pull on the lower unit, it will drop about 3/4" and then stops. As I pull on the lower unit and peer into the opening above the lower unit, I can see the water tube is coming out of the pump housing however the drive shaft doesn't come out of the pump housing. It moves down with the lower unit. Shouldn't the drive shaft come out of the pump housing as well?

Thanks again for all the help.


01-14-2007, 04:18 PM
I seem to recall that the shifter shaft must be disconnected from a clamp thingy up under the shroud. The shift rod turns in order to move the crash gears forward and backward and N in the middle. I think the clamp or whatever should be attached to the shifter arm. Once loosened off or removed, the shaft is free and everything should drop down. :huh:

Now something else comes to mind! I had a small outboard many many years ago that the shift rod was in fact split in half and that if you seperate the two pieces as you have indicated, you may see a clamp holding the 2 together. :smt038

01-14-2007, 04:23 PM
I just re read your note and see I never answered the question. The power shaft comes out of the base of the engine block. It does not come out of the gear case in the lower unit.

Tough Life
01-17-2007, 08:27 AM
You are right Dave, the gear linkage clamp thingy needed to be loosened and then the lower unit came right off. That's the good news.

The bad news is that the impeller is fine, so I must have a blockage somewhere preventing the flow of water. I'll have to track that down. Good thing I've got a few months before we'll be taking the dinghy out.

Thanks for all the help. Much appreciated.


01-17-2007, 12:30 PM
Hi Doug,

the impeller should be held in place on the shaft with a key. I doubt that the key would be the problem but I'd start there. If you pour some water in the pump housing does it run out of the inlet holes? If so, no blockage here. Can you force water up the pipe where the plastic water tube came from towards the block. I doubt you have a thermostat so water should come out the indicator hole. The indicator hole is just that; an indication that the water pump is working fine. Now for a final thought; I had a Yamaha 30 years ago and upon start one day I saw no water from the indicator hole. Panic!! Dear Lord my water pump is *%$$##! Not the case; a mud wasp had filled the outlet hole.