1983 Johnson 150 Operating Temperature Question

[Flats]

Well this is my first post to Iboats or any forum. Basically i have a 1983 non VRO Johnson 150 that was given to me. My guess is it was last ran about 15 years ago. So i rebuilt the carbs, both fuel pumps, replaced both thermostats and the related plungers ( everything under the thermostat cover). I also replaced the water pump housing and impeller.
Im not good with port - starboard but i will try to explain this as best i can. I got the motor running on the hose and it runs smooth and sounds good.
I got out the IR and shot the heads and this is what i got after running the motor for 15 minutes at 1500 rpm's (standing behind the motor) temps taken on cylinder cover (outside temp 50F) =

left side
thermostat cover 112
top cylinder temp 114
middle 118
bottom 126

right side
thermostat cover 119
top cylinder temp 125
middle 131
bottom 145

Based on the above numbers, i have a bad feeling that by the time the right side thermostat opens, the bottom right cylinder will be melting down. Is that a correct thought? I don't know the water flow route through the heads and block.

When i changed the thermostats, they looked REAL BAD - corrosion.
1. Should I have flushed water through with the ear muffs with the thermostats off?
2. should i pull the covers and see if there is corrosion and clean them?
3. skip question 1 and 2 and pull the heads and clean everything, replace diffusers, gaskets ect.

 

[Joe Reeves]

Re: 1983 Johnson 150 Operating Temperature Question

On a flushette, normal idle rpms are:
20" shaft engine = 1000 rpm
25" shaft engine = 1200 rpm

Running at 1500 rpm for fifteen minutes, I would strongly suspect that (especially with a new w/pump) that water is being forced thru and past the water bypass valves, defeating the purpose of the thermostats.

The thermostats open at approximately 143 degrees and the temperatures you quote appear no cause for alarm. Before going further, I'd suggest water testing the rig but before doing so make sure that your overheat warning system is functional.

Warning horn should beep when the key is turned to the RUN position.

With the engine NOT running but with the key in the RUN position, grounding out the Tan wire protruding from either cylinder head should make the warning horn beep steady and constantly.

Let us know what you find.

 

[emdsapmgr]

Re: 1983 Johnson 150 Operating Temperature Question

Joe's explanation is exactly on target. I'd run the engine in neutral when it's in the lake, when the idle speeds are lower (900?). Maybe in gear at 650 rpm's. Then laser check the head temps. You'll get all the water flowing thru the stats only, and that resulting temp will probably be 143 to as much as 155 (summertime normal.) When you get the boat on plane and those pressure relief valves open, you will commonly see those temps you are currently reading. When I plane out my boat in the cold March water temps, the temp gauge goes down below the 100 on my gauge gauge, only to return to normal when idling in neutral.