Johnson Outboard identity

[Frink]

Hi,<br /><br /> I just bought a used Johnson Outboard 100hp which I believe is a 1979 model. My model number is 100ML 79S Ser#J5137396 . Does anyone know anything about this particular motor? I have a slight problem with it over heating on the right-bank.When I took off the hose to the collector box, from the cylinder, the head it did not overheat. Is it alright to by-pass the collector box and run the water to the outside?

 

[ICEMAN]

Re: Johnson Outboard identity

Hi Frink, You do have a 1979 100 hp motor. There are two areas to check on this motor. One area is under the cylinder head on that side. There are water deflectors in the water passage. They divert the water around the cylinders. The other area and most probable is the thermostat on that side. The thermostats are located in what I believe you called the collector box. That is the thermostat cover. It sounds like you have a bad thermostat. I would not reccommend bypassing that area, the motor will run too cold and you may develop spark plug fouling and low speed stalling problems. Usually you have to remove the powerhead if the plate above the thermostat cover has the hump in it, Also there are springs and valves behind therm cover. Be ready for it to pop off when the bolts are loosened.

 

[Ross J]

Re: Johnson Outboard identity

Go with Iceman's suggestion, I've done this in the past with good results. Also the thermostat is a cheaper option than running too cold in the long run. <br />Ross