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Author Topic:   Evinrude overheating
dbssr posted 04-22-2004 01:22 PM ET (US)   Profile for dbssr   Send Email to dbssr  
Why does my 1980 15hp Evinrude outboard overheat? It pumps water for a while, then stops pumping and over heats. Is there a thermostat in this engine? If so, where is it located?

Thank you for any help you can offer.


Plotman posted 04-23-2004 04:26 AM ET (US)     Profile for Plotman  Send Email to Plotman     
Start by putting in a new impeller.
Clark Roberts posted 04-23-2004 08:13 AM ET (US)     Profile for Clark Roberts  Send Email to Clark Roberts     
dbssr, the OMC 9.9 and 15hp (low profile) engines of the 1970/80's vintage have very small "up" tubes (the tube that takes the water from pump up to power head) and sometime corrosion/deposits clog the tube where it enters the power head. When you change impellers try attaching a hose (you will have to fiddle around to find a correct size and clamp) to this tupe and flush system with water from hose. Even try to push a wire up to power head area to dislodge deposits. Thermostat is most likely located low on cyl. head and requires some great effort to remove since most of lower cyl is below the engines pan. I have had several of these engines and had cooling problems with all of them due to above. On one of the engines I had to remove the power head to get at the thermostat's fasteners and if I had to do it again I would cut access holes in the pan and be done with it.. Good luck...Clark ... Spruce Creek Navy
rbruce posted 04-25-2004 02:22 PM ET (US)     Profile for rbruce  Send Email to rbruce     

If you back flush wouldn't you risk to spray the pistons with water in the exhaust ports which could be open?

JohnJ80 posted 04-25-2004 08:39 PM ET (US)     Profile for JohnJ80  Send Email to JohnJ80     
I believe that they also have a water pump impeller that is rubber bonded to a brass bushing in the center (if it is the same as the late 70's motor my dad used to have).

What used to happen there is that if you didn't let the water soak the lower unit when you first launched it - maybe 5 minutes or so, the impeller ends would stick in the cavity against the side walls. When you fired her up, the stick there was stronger than the rubber to bushing bond and you would tear the bushing so that the impeller would not spin as it should. It often had symptoms like you describe - so you might want to check that too.

Incidentally, the fix after putting in 3 of these one summer was to just let it soak for a few minutes before starting the engine.


Clark Roberts posted 04-26-2004 06:29 AM ET (US)     Profile for Clark Roberts  Send Email to Clark Roberts     
rbruce, I'm suggesting flushing via the water pump's discharge tube so water route is same as if water pump is pushing the water. Not a problem and in any case the cooling water circuit is separate from exhaust gas circuit (incoming water is heated by the exhaust gases via the baffle plate heat exchanger)so no short circuit unless gaskets in baffle are leaky. Happy Whalin'... Clark... Spruce Creek Navy
andygere posted 04-26-2004 04:04 PM ET (US)     Profile for andygere  Send Email to andygere     
The thermostat is accessable on that motor, I owned one and had the same problem. It's on the upper left side of the powerhead, looking from the back. Make sure you buy the gasket for the small cover plate when you buy the thermostat. I cleared a blocked portion of my cooling system with a length of stiff weedeater line (very heavy monofilament). I rigged a section of clear plastic tubing to the tell-tail port, and connected it to a garden hose. With the thermostat out, no water flowed. After repeated efforts with the weedeater line, both from the tell-tail out end, and the water pump tube (remove the lower unit to get at this), I discharged the offending material. Water then flowed freely through the powerhead and out the thermostat hole. The blockage was caused by a bit of the rubber grommet on the waterpump housing that had broken off and lodged inside the powerhead cooling channel. It turns out that the @!$#%% repair shop that did the waterpump job for me last time did not replace the old grommet, and pinched it when putting the lower unit back on. The pinched part must have eventually let go and got stuck somewhere in the powerhead.

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