1961 Johnson Sea Horse 75hp V4SL-13 overheating after fifteen minutes idling

[Clippership821]

Got the boat in the water again this weekend. Figured out why it was dying on me. The choke was set to on. Duh huh!! Started like a dream again. Let it warm up and turned the choke off. (I'm not sure if the automatic setting is working so I set it to off to keep it running.) It kept running but there seems to be something wrong with the throttle. It just won't rev. Doesn't seem to be getting enough gas. [ I did recently replace the throttle cable. Anyways, after fifteen minutes of this the overheat light came on so I shut her off. So, that's where I'm at now. I just replaced the impeller. But, not the housing. Thanks for all your suggestions!

 

[Chris1956]

Re: 1961 Johnson Sea Horse 75hp V4SL-13 overheating after fifteen minutes idling

Clipper, In between the cylinder banks and down into the lower cowling is a black plastic housing. Inside is a thermostat with a heavy spring and a plunger with a light spring. The plunger pressurizes the cooling water to a couple of PSI. the thermostat causes the cooling water to recirculate until it warms up. it then is supposed to open to allow the motor to be cooled. The spitter should have 140 degree water exiting after warm up. You can check it with a meat thermometer.

You can run that motor without a thermostat, if needbe, but it is better to have one.

 

[F_R]

Re: 1961 Johnson Sea Horse 75hp V4SL-13 overheating after fifteen minutes idling

You can take the thermostat out for a quickie check, but don't take the pressure valve out. It has to be in there in order to cool. The 'stat probably isn't the problem anyway, but it is possible. They usually fail in the open position when they do fail. Usually, that is.

You probably should have replaced the housing. They usually are badly worn. Make sure both seals are good on the water tubes.

You said the boat was in the water, so I won't accuse you of running it in a bucket.

 

[Clippership821]

Re: 1961 Johnson Sea Horse 75hp V4SL-13 overheating after fifteen minutes idling

Thanks for the responses. I was wondering if the thermostat was suspect. Could leaving the choke set to on instead of automatic cause overheating? Also, what about not getting it to rev. I wouldn't think running at idle should cause overheating.

 

[F_R]

Re: 1961 Johnson Sea Horse 75hp V4SL-13 overheating after fifteen minutes idling

The choke will make it run lousy, but not cause overheating. If the water pump housing is worn it will be most noticeable at slow speeds. It functions as a displacement pump at slow speeds and as a centrifugal pump at high speeds.

I don't have a clue why it won't rev up. You are going to have to do some basic troubleshooting to figure that out. Compression, spark, timing, etc, etc.