1978 150 Johnson running hot.

[James R]

Motor is ok good comps. Carbs cleaned very thoroughly. Motor runs well. Cylinder heads white paint a little pink. Heads a little hotter than I would like.
Good water flow from telltale. Impeller in good shape. Exhaust cover cool.
pulled a thermostat and tested in a pan of water. A little slower to react than a new thermostat but operates. Ran motor for a short time with thermostat cover off and water came out. Fresh fuel and mix.Running on muffs. Dont have a local lake to put it in. Any thoughts?

 

[Eshaw150]

Re: 1978 150 Johnson running hot.

i have had the same prob the heads should get be to hout to put your hand on but not to burn you i acutally had the same prop with mine today on the water the horn went of i had a thermostat reaction to slow so i took them both out

mine will not pee unless in a body of water

 

[ezeke]

Re: 1978 150 Johnson running hot.

Your engines have 6 rubber water deflectors in the cooling passages around the cylinders. When one or more of the deflectors dislocate, the bank of cylinders will overheat.

You should be able to hold your fingers to the cylinder head for a full three count (no more because you can get third degree burns) any time that the motor is running.

If you find that one bank is running hot, you may want to take that cylinder head off and inspect the deflectors.

Also, The thermostat system has small holes which must be clear for the thermostats to work properly.