1979 Merc 20 hp questions?

TinBoats.net

Help Support TinBoats.net:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

acwd

Well-known member
Joined
Jan 11, 2012
Messages
281
Reaction score
0
Location
Albion, IL
I bought a boat, trailer and a couple of motors yesterday. Anyway on of them is a 20 hp Merc. The guy said he couldnt get it to pee. He put a new impeller in it and still no pee and the shifter was messed up. So I got it home and dropped the lower unit. Checked everything out. The seal that the water tube goes in was in there wrong so I fixed that. Blew air thru the tube into the block and the tell tale tube to make sure that there was no blockage. Put the thing in in a barrel fired her off. No pee. So out of the barrel and back on the boat. Put the muffs on it. Water ran out the exhaust when it was running but no pee. I let it sit and run for a minute or to then it started to pee. So I let it run a few minutes like that. Back in the barrel. Fired up ran for 15 to 20 seconds no pee then it started to pee and quit. So I blew air back thru the pee hole. And it started to pee regularly. Ok the question is how long should it take to start to pee? Its taking about 15 to 20 seconds. Normal? or does it still have some junk pieces of the old impeller floating around in the block? And how would I get them all out? Access cover? All of this is between the idle and start position on the handle.

Thanks
Steve
 
It surely sounds like there is still a blockage somewhere in the cooling lines. It should pee within 3 seconds is the rule of thumb I use.
Now you said you dropped the lower and checked everything so was the impeller in new condition?
 
When I replaced the impeller in my 20 hp a while back. There was a piece of old impeller wedged in to the top of the pump housing where the water tune goes. My impeller was not missing any blades so it was off another one. Wasn't having the problem what you were having in fact I was chasing oil in the lower unit when I found my bad impeller.
 
I've got a 75 model 20hp that I just put a new impeller in this spring. It takes about 4-5 seconds from initial startup before it starts to pee. So I'd say either your pump is a little weak or you still have some sort of blockage somewhere in the system. I'd pull the top off the pump housing and inspect the impeller, housing, plate, etc for any problems as well as checking out the water flow passages.
 
brand new impeller he even showed the package that it was in. The thing looks brand new. The only thing I can think is the gasket between the faceplate and the top of the pump isnt sealing good. Someone used a piece of rubber and made one so I cut one out of gasket material so I could a least try it out before I buy an whole brand new pump. I believe the pump thats in there is where the problem lies. The only place I didnt check was the water intake. there might be something in there. Started it this morning after sitting in the barrel for a day it did seem to pee quicker than before maybe 5 to 10 seconds.

Steve
 
Hook a hose up to the tube that goes into the water pump.(with lower off)Turn water on, it should come out of pee tube.
 
I'm no OB mechanic, but I would think that if you increased the thickness of the gasket between the upper and lower halves of the pump housing, that would open up some space above/below the fins of the impeller and allow water to flow around the impeller, making it less efficient. I'd also check to make sure the water tube fits snugly where it connects to the water pump so it can't be losing any water pressure there.
 
The gasket material that I used was thinner than (about half of the thickness) the one that was in there. The seals where the water tube go in seem to fit the tube tight. I will have to try hooking up the hose to the tube and see if anything comes out. And check the passage below the water pump. Order a new gasket and seal kit if I can get just those parts and try that if I cant get just those parts, a whole new pump.

Steve
 

Latest posts

Top