Johnson 200 Different Temp on Port side bank

Repair or modification of Boston Whaler boats, their engines, trailers, and gear
Iceboy149
Posts: 15
Joined: Thu May 03, 2018 6:05 am
Location: Crownsville, MD

Johnson 200 Different Temp on Port side bank

Postby Iceboy149 » Sun Jan 20, 2019 8:02 am

Thanks again to all who've helped me over the past few months. I have a 1990 Johnson 200 counter-rotating outboard engine with:
--new flywheel magnets
--new stator
--new timing base
--re-built carburetor
--[new] coil
--two 140-degree thermostats (white Sierra ones)
--new head gaskets
--new thermostat gaskets
--new spark plugs.

The engine hadn't been started in three years. At present it now starts fairly well. I run the engine out of the water on an ear-muff style hose adaptor. I meticulously cleaned the heads.

The port side cylinders were getting hot when running, while starboard bank stays nice and cool.

I took off port thermostat cover and thermostat and ran then engine; water pumped through the opening at a good rate. So some amount of water is getting to the port side of the block and no alarms ever went off for the few minutes the engine runs on the muffs. Then I tested the old black thermostats and new white ones in boiling water: both open, both close.

I removed both thermostats and ran engine. Still port side block now warm, not hot, but still starboard side very cool.

With both thermostats out, the water stream coming out of the engine did seem a bit weaker than before.

I dropped the gear case or lower unit. Everything seems to be in working order. The water pump is not distressed and all [impeller] fins are in tact. I will be replacing [the water pump impeller] this week.


Will I have a different/better result if I run the motor at the ramp, with a higher water level on the engine shaft?

Could I have a blockage somewhere inside the block on the port side?

Is anyone familiar with disabling the water control valve that I've seen on other websites for the engine?

Should I keep thermos out and just go run it at full throttle under load for a few seconds hoping to loosen up whatever might be in there?

On a side note: When first starting engine it didn't have a water stream, and I had to clear all hoses around discharge and water control valve of larvae and beetle cocoons.

Thanks again, Dave