1977 Johnson 200 HP Overheating

[NCBass]

Hello,

I have a 1977 Johnson 200 HP (model 200TL77C) that I just rebuilt because one of the top pistons (port) was gaulded up in the cylinder and seized up. I have run it for about an hour or so on muffs at idle speed, and she runs great. I took it to the lake yesterday tom test. The engine runs fine in gear at idle speed. I got the boat up on plane for about 30 seconds at WOT, then she bogged down and shut off. When I tried to restart, the starter would not turn the engine over even though the battery was fully charged. So, I took it home and pulled the plugs to see if I could turn it over. Same result. So, I pulled the heads and discovered that one of the top pistons (opposite side this time-starboard) was starting to gauld and had seized in the cylinder. The port side also had a few aluminum scuffs. I was able to break it loose by turning the flywheel nut with a big wrench. Upon further inspection, I found that the small water passage hoses had melted to the outside of the cylinder wall ONLY on the top two cylinders. The rest were fine.
My question is: Do you think I have a problem with my thermostats? I figured that maybe they are stuck open, and since water enters at the top cylinder these are the coolest cylinders and it may be causing cold seizure. The added friction then heats the cylinder so much that the water passage tubes melt. Or could it possibly be a lean condition at high RPM from the top carburetor? The plugs looked OK- a little discolored. Tops of pistons also looked good except the one that seized- it was totally black on top.
All help is greatly appreciated. Thanks.

 

[Bosunsmate]

Re: 1977 Johnson 200 HP Overheating

Did your temperature switch go off?
Have you a telltale?
Check for any head warping (combustion entering water jacket at high rpm)

 

[Bosunsmate]

Re: 1977 Johnson 200 HP Overheating

Id check the thermostats and the poppet valve too, those poppets get deformed quickly in heat

 

[NCBass]

Re: 1977 Johnson 200 HP Overheating

I am not sure if I have a temperature switch. If so, where is it located? The tell tale is peeing good. I just put a new water pump in.
As far as the thermostats, this is one component that I did not replace when rebuilding. The rubber seals were gunked up with white flaky stuff, but I cleaned them really good before reinstalling. The little plastic pressure relief valve was slightly deformed from the original overheat. Would a faulty thermostat cause the cylinders to overheat more on the top cylinders than the rest? This may have been the original cause of the failure before rebuild.

 

[Bosunsmate]

Re: 1977 Johnson 200 HP Overheating

Yes there are two temperature sensors
Part #386686 they are on the back of the heads by the thermostats. Try grounding a wire from them, normally its a brown wire and theres a joiner you can split in a rubber boot on the line. Listen as to if your sensor horn goes off- ignition must be on.
Slightly deformed poppets can cause the problem as they wont move in the grommet housing so you wont get enough water at higher rpm.

I grinded, sanded mine down a bit so they moved easier than they are probably meant to so they have much less chance of getting stuck
Yes id say a faulty thermostat/poppet could cause top cyl to overheat first as the reduced water intake would drop away quickly from that height and not be able to cover the whole surface area properly before doing so

 

[Bosunsmate]

Re: 1977 Johnson 200 HP Overheating

Check your top bypass covers for air leaks too
Did you inspect the upper crankcase seal when you rebuilt it?

 

[NCBass]

Re: 1977 Johnson 200 HP Overheating

Thanks for the info. I found the temp sensors. As for the repair, I am going to purchase two thermostat rebuild kits and install them. I will also take the carbs apart and clean them again. Hopefully this will solve my problem. I will update post when I have done this.
Again, thanks for the help.

 

[NCBass]

Re: 1977 Johnson 200 HP Overheating

When I rebuilt the motor, I had the cylinders bored. I replaced: pistons, rings wristpins, clips, upper and lower rod bearings, main bearing, and the complete set of powerhead gaskets (including bypass covers and crank seals). There are no air leaks.

 

[Bosunsmate]

Re: 1977 Johnson 200 HP Overheating

The warning horns from that era i find are really low in volume, only practicably audible at idle.
When i do test runs i put my ear right down by it and you can hear it there or i throttle back to idle and check if its going.
cheers

 

[emdsapmgr]

Re: 1977 Johnson 200 HP Overheating

Your engine suffered a high rpm overheat lockup. The piston/s got hot enough to expand and lock in the cyls. That's why the starter would not rotate the crank after the lockup. That engine got pretty hot if it melted two of the rubber water deflectors. When the cyl gets that hot, the incoming fuel/oil mixture just can't keep the cyl lubbed and it'll scuff the piston/cyl. Something is going on, perhaps in your thermostat housings. When the engine idles, all cooling goes through the two thermostats. If they stick shut, no cooling water will flow thorugh the powerhead at all, even if you have a new impeller. Once you get up on plane, the nylon pressure relief valves will open and should permit tons of extra water to flow through the powerhead, and should provide enough coolant for the powerhead to keep cool-as long as you are planing. (If you go back to idle, it'll overheat.) As such, it's unusual to have an overheat lockup if you were planing at the time. However, if the nylon pressure relief valves were already deformed due a prior overheating condition, it's possible they did not function normally, causing your overheat while on plane. I read the observed damage which caused you originally overhaul the powerhead: did you ever find/diagnose the reason for the original failure? Sounds like the same thing all over again. Do the two head overheat switches work-sound the horn if grouned? It's normal to replace the stats and visually check the nylon pressure relief valves at overhaul time.