115 johnson ran hot

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Old 06-26-11, 11:08 AM
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115 johnson ran hot

Hello,

I've got a 115 Johnson from the mid '80s. It got a big once-over earlier this year at the johnson dealer and had $980.00 worth of stuff done (carbs, head gaskets, throttle cable, tune up, etc...). It ran great.

I took it out fathers' day and went to our spot 6 miles from the landing. As soon as we got to the spot, the boat started slowing down. I let off the throttle immediately and it shut down. At that time I smelled something hot and knew I was in trouble. I looked over the back and the motor was smoking. I let it cool for 30 min or an hour and tried to start it again. It would start but die and I had to choke it a lot. We got back to land (a whole story by itself) and now it's at home. I haven't done much with it yet, but I put the dog-ears on it and turned the water on, and cranked it up. The water pump is working. The engine will run revved up but it misses a lot and the lower I run it, the worse it runs. It won't idle.

I noticed the head gaskets appear to have beads of water on them after running, so I guess I need head gaskets again. I also noticed one of the hoses coming from the thermostat housing is collapsed. I pulled the plugs and one of them is rusty and wet with water. I didn't put a gauge on it, but when stepping on the prop with the motor in gear, all 4 compression strokes seem fairly strong without a lot of leakdown, so I think the pistons and cylinders are still ok.

I am a mechanic, but boat motors are foreign to me. My thinking is that I need to pull the heads and inspect and replace the gaskets, pull the thermostat housing and replace the stats and hoses, and pull the foot and inspect the impeller. Am I thinking right, and are there any other things I should do or look for? I don't know why it ran hot in the first place unless the one collapsed hose could do it. Can I add a temp alarm to this engine?
 
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Old 07-02-11, 06:34 PM
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Well, in case it may help anyone reading this during their research for a solution to their problem...

I pulled the heads and one cylinder was obviously water contaminated, although the gasket showed not signs of being blown. I cleaned the surfaces and found out the heads were warped. I re-leveled the heads and installed new gaskets, replaced the water hoses, and put a water pump kit in it. It cranked up and ran beautifully. I still need to research a temp alarm or at least gauge. Now I have some repairs to do to the trailer. Somebody did a butcher job putting a new axle under it.
 
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