1951 Evinrude 7.5 won't pump water

[nitrocharger]

I have an old Evinrude Fleetwin that I fixed up (or so I thought) but I'm having trouble with the cooling system. When the motor first starts up it pumps a good stream of water then after about 30 seconds or so slows to a bunch of steam. I have a brand new impeller and water pump housing. Ive gone through everything in the lower unit and it looks normal. Ive tried running this in a bucket of water and on the back of a boat with the same result. The interesting thing is if I let the motor sit for a minute after I stop it then start it back up it will pump for a short period of time again. My guess is maybe there is cavitation or exhaust seeming into the intake side of the pump? Has anyone had any similar problems? This thing is driving me crazy.

 

[oldcatamount]

Re: 1951 Evinrude 7.5 won't pump water

That sounds like a blockage in the water jacket to me. I'd suggest removing the lower unit and rigging a garden hose to the copper water tube, remove the T-stat and lay the motor on the floor face up. Blow some water through it. You can also do this procedure using compressed air instead of water. I've also had some luck using a length of weed whacker string to probe around in the water jacket behind the T-stat. Look the T-stat over closely, it to could be the problem.

 

[Joe Reeves]

Re: 1951 Evinrude 7.5 won't pump water

When the motor first starts up it pumps a good stream of water then after about 30 seconds or so slows to a bunch of steam. I have a brand new impeller and water pump housing. Ive tried running this in a bucket of water and on the back of a boat with the same result.

If when running in a barrel or sitting in neutral when on the boat, the water level is above the water pump (pump is not self priming), then I would suspect that the pump is not sealed properly OR the head gasket is failing slightly which allows the combustion to enter the water passageway which in turn results in a stalemate..... water coming up, combustion going down, water stops and boils. There is no thermostat in that early model.

 

[HighTrim]

Re: 1951 Evinrude 7.5 won't pump water

Im with Joe, there is an air leak somewhere.

 

[boobie]

Re: 1951 Evinrude 7.5 won't pump water

Take the l/u back off and seal the water pump hsg and the plate below it with 3M-847 sealer.

 

[nitrocharger]

Re: 1951 Evinrude 7.5 won't pump water

So a little update on where I'm at;
I attached a garden hose to the water flush port and removed both spark plugs to see if there is a leak in the head. Water came out of just about every hole or port in the lower unit. I know there was a lot of pressure because the side vent was shooting water about 7 feet. I didnt see any water come out of the head but I did notice some from the heat exchanger leaking from the screws (took it off last night and probably needs a new gasket).

I removed the heat exchanger and saw some water in the bottom of the lower cylinder. It didnt look like it came from the heat exchanger leak so I thought it must be from either the head gasket or the water pressure blew up through the shaft into the crankcase. I've never removed the power head so I'm not sure if thats possible. I also pulled the head and while the gasket doesnt look great, it doesnt look like it was leaking either.

What would you guys do next? (hanging it on the wall as decoration has crossed my mind)

 

[nitrocharger]

Re: 1951 Evinrude 7.5 won't pump water

As I was waiting for my new gaskets to come in I started cleaning the aluminum plate that is part of the heat exchanger and noticed 2 tiny pinholes where the water side had corroded through. I didnt notice them before because there was exhaust gunk all over them. I see that the cast cover p/n is 203374 but is there a part number for the aluminum plate? Do they make a stainless version that wont corrode or is aluminum the only suitable material due to its excellent heat conducting ability? I'll figure this thing out someday...