Thermo Switch - Johnson '76 115etl

[newtong_ware]

Can someone tell me the purpose of the thermo switch? I understand the where and why of the thermostat and the temperature alarm (horn) switch. But I am doing a rebuild and I need to know what this item does, if I should replace it, and the best way to do that if so.

Thanks,
Newt

 

[ezeke]

Re: Thermo Switch - Johnson '76 115etl

The switch closes the circuit on the horn when the engine overheats, causing the horn to sound so that you can turn the motor off before more damage is done.

Because the switch does nothing until a problem arises, the cause of the overheat may go undetected before some damage is already done. Many people have added temperature gauges to get better advance warning, but I don't know of anyone who has disabled the horn/switch.

The switches don't usually go bad, but should be tested periodically. It is much more common for the horn or the wiring to have problems.

According to the factory Service Manual, the temperature switch closes at 211º F +/- 6 º and reopens at 175º F +/- 7º. [ pg 5-4]

 

[jimmbo]

Re: Thermo Switch - Johnson '76 115etl

Some early and mid 70s Johnrudes used a choke that was controlled by a thermo switch. From what I gather it held the choke partially open/closed until the engine reached a certain temp(145 degrees) then it allowed the choke to fully open.

edit: should have said ' some 1968, 69, and early 70s'

 

[ezeke]

Re: Thermo Switch - Johnson '76 115etl

The switch that controlled the choke was located at the top of the engine at the lifting eye and was activated by low temperature. Most of them were removed by service departments and my 1976 115 Johnson never had one to begin with.

If you are referring to the choke thermo switch, here is a link to a recent thread that may help.

http://forums.iboats.com/bbBoard.cgi?a=viewthread;fid=28;gtid=1249007;gpid=1250067#gpid1250067

The switch that controls the horn is located at the cylinder head and has a tan wire.

 

[jimmbo]

Re: Thermo Switch - Johnson '76 115etl

Sorry, I didn't know when OMC discontinued that item

 

[newtong_ware]

Re: Thermo Switch - Johnson '76 115etl

Hey ezeke. Good info sir. Exactly the part, the thread read just like my own experience. I will follow the SB directions. I knew the alarm horn was different and that this device had two wires going back to the terminal strip.

Thanks again.

>>>>Newt