71 50 hp overheating

[fishn_n_tx]

I have replaced the impellar and thermostat. The water jacket under the cover looked as clean as could be expected when I replaced the thermostat. The pressure relief valve and spring looked to be in good shape. It is getting hot, too hot to hold your hand on. But only getting hot on occasion.<br /><br /> What are the most common causes of overheating? <br /><br /> I was thinking I might loosen the bolts on the waterjacket cover and start it to see if there was any water pressure at the cover. When idling, It pumps the water out of the exhaust vent towards the top just under the cowling cover. When underway I can't see it coming out anymore, but I think it might be all going out the prop hub at high speeds.<br /><br /> I was told to blow air thru the up tube to make sure there is no obstruction, but I dread dropping the lower unit with the selectric shift wires. Would it do any good to just remove the waterjacket cover on the top of the head and put the hose to the thermostat hole and the pressure valve hole and flush it that way?<br /><br /> Could reed valves or anything else be causing it to overheat. Could a cylinder be scored and just making too much friction. It seems to run great, just getting hot.<br /><br /> Another note, I think I solved the fuse popping problem. The red wire on the rectifier lost some insulation and looked to be grounding out on itself.

 

[ledgefinder]

Re: 71 50 hp overheating

Is your overheat alarm going off? The correct temp for the block feels pretty hot (to me anyway).

 

[fishn_n_tx]

Re: 71 50 hp overheating

Yes, the buzzer does go off. Sometimes I can go a mile or so and sometimes a couple of hundred yards. May try a new sensor next.

 

[oscar boy]

Re: 71 50 hp overheating

Fish I had a 1981 50hp Evinrude that would set off the heat alarm if I putted along at slow speed for over five minutes. If I would open the throttle up the alarm would go off in about two hundred yards.<br />I changed impellers, thermostats, and relief valves several times. Finally I pulled the head off expecting to find the water jacket plugged, but it was very clean.<br />What I did discover was the head gasket was leaking hot combustion gas into the water jacket at slow speed. At higher speed the increased water flow was enough to cool it down.<br />Don't know if this is your problem but it solved my heating problem.

 

[JRuggiero]

Re: 71 50 hp overheating

Don't fear dropping the lower unit with the hydro-electric shift. I just did it on my '71 60hp evinrude.<br /><br />Tilt the motor all the way down. Disconnect the knife connectors for the blue and green wires (just under lowest spark plug under rubber tubes). Take out 5 visible bolts on lower unit, then remove the anode. There will be one more bolt hidden up there. Then the unit just drops. I'd tape a piece of wire or string to those knife connectors to make it easier to pull back through when putting back together.

 

[fishn_n_tx]

Re: 71 50 hp overheating

I pulled the water jacket cover off the head, ran the motor in a barrell and it was pumping water out the thermostat hole and the relief valve hole. So I know the water is getting that far. Reinstalled the relief valve but left the thermostat out. Took it out this evening and made a lap around the lake. No buzzer. The water coming out of the very top vent when it is idling is warm, so I know its passing over the head. Will give it another try tomorrow and will have time to run it longer. I'm guessing no thermostat won't cause any problems till its cold out?<br /><br /> I'll give the head gasket a try too. Simple enough to replace and probably due for one. I would also like to take a peak into the cylinders.

 

[oscar boy]

Re: 71 50 hp overheating

Fish n tx If you will e mail me I will e mail you a diagrahm of the water flow on that motor. <br />bruno@exp.net <br />Does the motor run hot at high and low speeds. To change the head gasket I took the power head off.