83 Johnson 90 idle

This forum has been great to me trying to get my 90 to run perfectly.. I have had good help with the cooling system and now it pumps really well.. Maybe to well though. The block seems really too cold to my touch and using a digital thermometer I see temperatures after running at the dock of about 107 degrees. I replaced the thermostats during the water pump job. Are they not working or is there something else that I missed? I tested them in water on the stove and they opened at 140 degrees. I also noticed after trolling for a half an hour or so a lot of black oilly soot on the mid section (freshly painted white). Could this be too cold engine? Also I have noticed the engine slowing down when I trim the motor down while manuvering to my dock and it sometimes stalls. If I trim the engine out it seems to clear up run smoother? We are getting closer to getting this engine perfect. I am an old Merc guy and learning about how these cross flows work is fun,,,thanks Bill

Re: 83 Johnson 90 idle

The engine has two temp ranges. When idling, the thermostat should open at 143, and should idle in the 140-150 range. When at planing speeds, the pressure relief valves open,providing extra cooling water. The powerhead temps can go down significantly when running at higher speeds. 107 is cold, if this is an idling temp. Did you put the thermostat pressure relief valves back in the housing? You really want the engine to get up to normal operating temps for ideal performance, long engine life and fuel economy. Black oily soot around the midsection could be the sign of a bad powerhead base gasket. A typical failure on these old crossflows. You may also be getting exhaust smoke under the cowl when the base gasket fails. When you trim the engine outward, it tends to run leaner since the engine is not as deep in the water. When tucked all the way in, it will run slower due to exhaust backpressure. You should set the "normal" idle speed when the engine is fully down and sitting normally in the water.

Re: 83 Johnson 90 idle

Took the engine out with the cowel and the airbox removed to run hard after decarbonizing and to get some more temperatures.. Is there a way to look down in the water and see when the thermostates are working? Are the round holes above the cavatation plate the exit for this operation? After running the engine wide open and than idling back to my dock, I was seeing about 130 degree's on the top of the the block just before the head. I feel the base gasket is good maybe its too cold. Could the link and sink adjsutment be off and is this difficult to do?

Re: 83 Johnson 90 idle

130 would be a good temp number if you had just run it hard. The extra coolant provided by the open pressure relief valves will cause the temps to drop and this is a good planing speed temp. You should determine what it is after idling at the dock for a while, when the relief valves are closed. It is always a good idea to confirm the sync and link settings, esp if the engine is new to you. These settings should have no effect on the temp issue, but will affect performance and overall driveability.

Re: 83 Johnson 90 idle

Once back at the dock it appears to cool down again.. Is there a better thermostate? If so I will replace.. I will attempt the link and sink deal next time out,,,, thanks.. very mcuh again

Re: 83 Johnson 90 idle

Did you reinstall the pressure relief valves/springs in the thermostat housing?

Re: 83 Johnson 90 idle

I know that the check valves and springs are in the housing as they are new , but now I wonder if they may be installed incorrectly. Can they go in wrong? Or could they be stuck open or jamed.. Is there a diagram of the installation.. thanks

Re: 83 Johnson 90 idle

Possible that the pressure relief valves are remaining partially open at idle, causing low idle temps. The parts catalog has a nice picture of the thermostat housing and components. You can look it up online. epc.brp.com.