Mercury 20Hp impeller/water pump location

Question edited for clarity, but needs engine model and HP.
Question moved from Dishwashers.

Some ideas here. Check that the impeller spins (the drive is okay), but it sounds like you have blocked passageways.

https://www.google.com/search?q=1993+Mercury+Outboard+Engine.+Why+is+it+not+peeing

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Question edited for a lot more clarity and correct spelling of the maker.

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was the impeller installed correctly for the drive direction
if not it will not pump water
next to check is the plate between the water jacket and the exhaust
that plate gets eaten away and allows the water to go straight out of the exhaust

Hi Bill:
According to this link it looks like it is 1974
http://www.maxrules.com/models/Merc_model_files/15-25.html
Cheers

If your old engine/control has the same 'options' as the30hp, yes everything is compatible... (Electric start or trim )
The throttle and shift cables are allways compatible...

Check here, you'll need the horsepower and lookup the serial-number range...

http://www.iboats.com/basics/serial_number_year.html#mercury

Go to boats.net - Mercury parts - search under hp/serial range - select 20hp 2 cylinder - it will be under the first selection 0A730007 and up.

if you mean a large flat sided 'O' ring then this is to help keep water in the impellor housing !? some housings have gaskets between the base plate and housing , check the impellor in the housing and see if it stands proud as then you need the gasket ! compare with the old one as it mite have been forgotten !! check the seal and tube for the water pipe also ok!

The water pump is a flexible impellor located in the top of the bottom section of the leg of the outboard. It is driven by the drive shaft to the prop that is spinning all the time the motor is running. You will find it behind or near the water inlet slots at the bottom of the leg

water pump-
crack in the housing from sitting over the winter with water in it