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Help with 1977 Johnson 85 hp overheating only at high speed

Woodcrafter0621

New member
My 77 Johnson 85 hp is overheating at high speed only I have replaced the water pump and checked the veratherm in boiling water everything seems to be fine. Not sure why the alarm is going of when in full throttle only, any help would be great.
 
When you replaced the water pump were all of the impeller fins in place, or were some broken off. If some were missing, they are likely lodged somewhere in your water jacket. You might try removing the thermostat and inserting a garden hose in there, seal it off with a rag, and force water through the system at the highest pressure you can get.

The other alternative is that your water temperature sensor is bad. Run the engine with the cover off and use a heat gun to determine what the temperature of the heads and manifolds really is.
 
When you replaced the water pump were all of the impeller fins in place, or were some broken off. If some were missing, they are likely lodged somewhere in your water jacket. You might try removing the thermostat and inserting a garden hose in there, seal it off with a rag, and force water through the system at the highest pressure you can get.

The other alternative is that your water temperature sensor is bad. Run the engine with the cover off and use a heat gun to determine what the temperature of the heads and manifolds really is.


Thanks for your help I will do some checks for temp. But could I remove one of the hoses going into the veratherm and put a hose into the head to back feed the water with high pressure? Would that damage anything? Maybe it would clean the water jacket?
 
I'm not that familiar with that engine, but I doubt it would cause a problem. You may want to post this issue on the Johnson/Evinrude forum. Go to the top of this page and on the left, click on "Forum Home." Then click on the Johnson Evinrude forum.

If you are operating in saltwater, then there is a distinct possibility that you have corrosion and junk in your water jacket and exhaust tubes. I know of no practical way to fix that. Some folks I know will use a product called "Salt Away" to clean that corrosion out, but with very mixed results.
 
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