1967 100HP Johnson, Overheating?

[exodave]

Hi Guys, I bought this Golden Meteor 3 months ago. After successful carb rebuild, new impeller, power pack, coil, and a few other misc parts, I've had about 15hrs of very satisfying running time with it on the river.

Saturday, I failed at navigating and allowed First Mate Girlfriend to run us aground. Afterwards, I idled us the 100 yards to our marina, frightened as all get-out of what damage we might have caused. As I pulled into our dock, the engine suddenly died then ran rough, sputtered when I tried to restart. When I took the cover off, it just seemed really hot in there, smelled like melting plastic. I just assumed the temp switch that is supposed to trigger the light on the dash was bad, since I haven't tested it. I left it to cool off while I gathered the courage to inspect.

Climbed into the muck and pulled the lower unit today. Pump seems good, found no dirt or sand or any blockage in the pump or waterways I can see. Impeller still looks new. I inspected the powerhead for cracks, found none. Started the engine, it sputtered a bit, then took off racing, water flying out of the port just above the lower unit at the rear, seemed to be running lean which I can almost blame on the rapidly cooling weather. I adjusted fuel/air mix, it idled well. I watched it come to operating temp, kept touching the cylinder heads. After 5 minutes, the cylinder heads were hot enough to boil water splashed up on them, but the rest of the engine including the bracket that holds the temp switch remained cool to the touch.

Are we overheating or do the cylinders generally get that hot at normal operating temp? Could there still be some blockage up in the powerhead somewhere? I don't really know what to do next except perhaps just pour some boiling water on that temp switch to see if it's actually working. It's getting time to go way out into Lake Erie and get more of those perch and bass to fill the freezer, but I'm not confident at the moment that I won't be stuck out there. What should I do next?

 

[boobie]

Re: 1967 100HP Johnson, Overheating?

Did you actually put water on top of the block and did it boil ?? Check your temperature with a temp gun. It's the only way.

 

[exodave]

Re: 1967 100HP Johnson, Overheating?

Yeah I dripped some water on top above the spark plug on both sides and it vaporized. Are there actually cooling waterways going around those cylinders? If so, I'm beginning to think it needs to come out of the water for the season and get those cleared out. There's no way it should boil off like that at 160f or whatever the appropriate temp is, right? I was planning on replacing the head gaskets and such over the winter anyways.

 

[boobie]

Re: 1967 100HP Johnson, Overheating?

Good idea. Pull the heads and see what you find.

 

[exodave]

Re: 1967 100HP Johnson, Overheating?

Took one more swing at it - pulled heads and thermostat housing and lower unit again at the dock. Everything looked fine, no blockage, except the outlet copper pipe from the water pump was a bit misaligned so I straightened it up. Ran water through all ports that I could see and watched it run back out the exhaust and the two pipes going down to the pump. Reassembled, started, ran at something like 1500-2000rpms or more for 5 minutes in neutral and the laser temp gun shows 200-220f near all spark plugs and down to 150-160 around near the base of the cylinders.

Since the motor is new to me, I'm afraid it may have just been running this hot all Summer and I would have had no idea, so I feel stuck. Any ideas/suggestions? Any chance this old motor just runs this hot?

 

[exodave]

Re: 1967 100HP Johnson, Overheating?

Problem solved! It was the stupid thermostat, although I don't quite know if or how running aground did it in (unless we were running hot all Summer). I simply removed the guts from the thermostat, and now we are running under 105f on the heads even up on a plane. I understand this is below optimum temp, but until the new vernatherm arrives, I'm assuming the only problem that may arise is difficulty in getting a smooth idle on a cold morning?

On another note, I noticed an even film of carbon buildup in the cylinders and on the piston when I had the heads off. I did perform a decarb earlier this year with a can of decarb foam I got from Boater's Value. Do I need to get in there and mechanically remove the rest, or is it possible the foam would work better now that the engine is not overheating? If I need to remove the carbon manually, what's the best method?

 

[exodave]

Re: 1967 100HP Johnson, Overheating?

Finally getting around to an end-of-season update on these threads.

Right before I took her out of the river for the season, I reassembled the thermostat with a new vernatherm. After idling for a few minutes, the temp seemed to be spiking and I wasn't impressed with the amount of water coming from the telltale. So, I simply took the vernatherm out again while I dealt with other issues (such as the engine fire I had), then immediately ran it to the last open ramp to put it all away for the season.

Now that I'm doing a thorough restoration on the motor in the garage over the winter, I noticed the fire destroyed the telltale tube. I'm not exactly sure now if there is still a problem or not, but I'm clearing out every waterway I can find while I have the motor in pieces, replacing the impeller, and installing a working high temp switch. Hopefully, when it's all back together and running in a barrel next month, all problems will appear to be solved.

Edit: BTW, it was really rough getting the motor up to temp with the vernatherm removed while fishing Lake Erie in November. Hope I don't have to do that again.