1974 Johnson 15 hp thermostat question

[bently]

Can I bypass the thermostat on my outboard by replacing it with a washer with the same inside hole diameter as what the thermostat openning would be? How would the engine be affected? smaller hp johnson just have a small hose which shows water flow without a thermostat, is there a certain hp size where thermostats are used?

Thanks

 

[racerone]

Removing the thermostat from a 1974 Johnson 15 would be a mistake !!!

 

[kbait]

You want your outboard to reach optimal operating temp and stay there. Removing thermostat, even w/installing restriction, will cause your motor to run cool... which leads to more fouled plugs. The 'low tension' points ignition system on your motor tended to foul the occasional plug anyway, and removing thermostat will just make it worse. Also, use NGK B7HS gapped to .030" in your motor.

Good luck!

 

[bently]

What is the temp that the thermostat is supposed to open, The motor runs fine in a test tank but out on the lake it acts like it is only running on one cylinder at midrange and at WOT. It will idle and troll around on the lake fine and low speeds, the water seems hot spitting out of the above water line hole during midrange and WOT short runs and then the motor bogs down. I can test the thermostat openning temp in my test tank but I need help fixing the bog isssue. I have one of those laser heat guns to shoot the head/water jacket while in the test tank which will tell me if my thermo is bad or weak.

Thanks

 

[bently]

I do have a new water pump impeller which should be here this week, where is the engine supposed to spit the water out so you can tell if the water is circulating well. thanks

 

[dukchunter]

All of us conditions lead us to believe that u r motor is overheating. Most likely your thermostat is not opening or at least not fully opening. Pull it put it in a pot of water on the Stove and see if it opens. If it does open check the temp that it does. Most likely it's bad. That is why your motor runs good until you open it up. It's not getting the cooling you need.

 

[kodibass]

Is/has your motor been run in salt water, if so suspect the upper grommet your motor has the old style grommet, these are known for collapsing and causing water restrictions. at the base of your power head.

 

[bently]

the thermostat starts to open around the 150 degree mark and fully opens around 160, it is supposed to be a 143 degree thermostat. I believe it needs to be replaced. My motor has only been ran in fresh water. The story about this motor is it was purchased new by my grandpa in '74 along with a Lund s-14. The motor was sold about 5 years ago and I ran into the guy who bought it and he offered to sell it back to me. I told my dad about it and he was glad I bought it back and now it is back on the original boat it started on and my dad and I are planning on using on some small lakes we used to fish 30 years ago with his dad.

 

[AlTn]

a lot of useful info about this series of engines can be found by googling " Leroy's Ramblings"..9.9/15 hp. johnson/evinrude maintenance and repair

 

[bently]

I installed a new thermostat & gasket, added "pee hole" to show the water pump is pumping. When I shoot the outer water jacket with the lazer heat gun, the highest temp I can get is/was 135 dgrees. I can touch and hold my fingers on the water jacket and head for 15 to 20 seconds. The new "pee hole" shoots a good stream, is there anything else I need to check or test?

thanks