1989 Johnson 120 overheating

[hdp951s]

1989 Johnson 120 HP overheating. I have replaced the waterpump, thermostats, and temp. sensors.

I can run at 3500 rpm with no problems, over 4000 rpms, the buzzer goes off and cuts throttle.

Can anybody help? Is there anything else in the cooling system to replace?

 

[jonesg]

Re: 1989 Johnson 120 overheating

Could be bits of old pump in the water galleys, backflush to get rid of that stuff. Have to drop the leg.

Are you sure its an overheat condition?
What temp is it running?
Have you tried holding a hand on the head at least?
iBoats sells temp guage with sensor for $40.
Kinda handy to have one in the dashboard.

Could also be a bad sensor.

Do you turn the engine off to reset the overheat ?

 

[Ray.W]

Re: 1989 Johnson 120 overheating

How do you backflush? I hooked up a flush kit to the intake ports but can't get any water through to the discharge ports or the water pump indicator. I can blow air back through the indicator hose so that doesn't help. I don't know what is plugged.

 

[kenmyfam]

Re: 1989 Johnson 120 overheating

You may have to whip the heads off and replace the water deflectors. Worth a good back flush first though. If it is indeed a water flow restriction. Make sure the sensor is not malfunctioning.
Illustration courtesy of another iboats member.