78 Johnson 85 Horse

[mattloomis23]

I have a 78 Johnson 85 horse with the alarm going off after 60 seconds of full throttle. I had a new water pump kit installed and have removed the thermostats. I have a new thermostat kit to install but read that it was ok to temporarily run it open.
The problem is that the alarm goes off after running wide open for any length of time. I believe the alarm is working properly and not defective or shorting out. Just wondering what to dismantle next? Why this common problem with this V4?

 

[racerone]

Some will argue.------I would first do a compression test.-----A blown head gasket can cause overheating.------The parts book shows what is called a " deflector " in the water jackets.-----These guide water around the block for proper cooling.----They are pieces of hose that can swell / move to block water flow.-----Note that water does NOT flow through the hoses.-----Remove cylinder head to inspect these.------Remove cylinder head water jacket covers too.-----Salt water motor ?------This is easy work on a fresh water motor.

 

[timguy]

An even slight compression leak into the water jacket can disrupt cooling water circulation. Without constant and complete water flow around head and cylinder, it will create hot spots. If corrosive deposits are present, this magnifies the problem. There are more threads this time of year involving salt water motors of course.