1975 merc 50 hp cooling problem--HELP

[MADMERCOWNER]

Okay heres the problem. The other day I went to put the boat in the water and when I started it no water came out of the pee hole. So some times I have to give it a little gas and then she starts to pee. But she didn't pee so I pulled her out and changed the water pump. Not a hard job but after I tested it one the water she took more RPM'S then usuall to get her to pee but it did pee. The water that was coming out was very hot and at idel it would stop to pee and steam or exaust came out instead. But if I gave her some RPM'S she would pee again. But not like it did with my old impeller. But when I changed the impeller mine was missing vanes and was in rough shape. So I check for blockage and air pass right through with no problem. So I check to make sure I have compression and all is fine (1-130, 2-125, 3-123, 4-120). All the plugs are dark and everything seems fine there. I'm wondering if someone has some other ideas.Hope some one can help me. Thanx

 

[12Footer]

Re: 1975 merc 50 hp cooling problem--HELP

Remove the thermostat.run it about 10 minutes without the thermostat, then install a new<br />thermostat. No doubt, when the vanes left the impeller, they ended-up in the water jacket somewhere.Don't run her much longer then 10minutes without a thermostat tho. It will warp the head, exaust port plate, or both, from running at unequal internal temps. But the idea here is to flush the water jacket out as best you can. If this engine sees a lot of salt water operation, you may have blocked ports around the head and manifold,requiring removal and cleaning.

 

[MADMERCOWNER]

Re: 1975 merc 50 hp cooling problem--HELP

Found the problem. It was the flush screw on the side of the lower unit near the water pump.It was very lose and water was jetting out from there instead of going up to the motor. That was the cheapest repair ever. I was thinking of removing the exaust plate and head. WOW

 

[tmcalavy]

Re: 1975 merc 50 hp cooling problem--HELP

Just an FYI, the Merc 500 50 hp doesn't have thermostats. Mine does the same as yours. I'll have to check the flush plug.