[Dudeitsmattx]

Impeller or maybe the thermostat is stuck closed.

 

[Brett]

Reasons for loss of water pressure?

Ones I've had to deal with:

1) Blocked intake, usually mud, from running too shallow
     or mud wasp building a nest when boat stored outside
2) Worn impeller, blade tips/edges abraded by silt or sand
3) Impeller detached from metal core
4) Impeller housing seals no longer seal
5) Bad seal where water tube enters block
6) Blocked water jacket
7) Blocked or frozen thermostat
8) Blocked feed to pisser tube
and
9) The worst one, sheared drive shaft just above the impeller housing

One other thing, if I take the time to drop the lower unit
and I can tell the impeller hasn't been serviced in a long while
I don't just replace the impeller, I replace the housing and all seals.
The kit isn't that much more in price, than just the impeller.

 

[noeettica]

Buy the factory service manual

and follow Brett's check List ...

Good Luck

 

[UFgatorbait]

after taking the lower unit off i discovered the problem you can tell the impeller has seen better days…I replaced and changed seals and put near gear lube and its running like a champ. ;D

 

[Brett]

Yep, the neoprene blades get brittle over time and fragment.
That's why it's recommended that you replace the impeller regularly.
The recommended interval is 100 hours or every other year.