Re: How does the thermostat work in this 1995 130HP johnson outboard?
I had both thermostats in my hand and I can for the life of me figure out how the thermostat itself works. What does the little brass thermostats do as they heat up to temperature? How does it open the passage to let the coolant water flow?
Although this is an old question, it was never answered, and since I had the same question and now at least think I figured it out, I will answer it here for future reference. I have a Johnson 130, 1996 - same boat.
After running through some shallow water, I got high temp alarms. I pulled the thermostats to clean them, and sure enough they were caked with sand. Some vinegar soak dislodged more of the sand. But I wanted to make sure they still worked. So here is what I found.
I purchased one new stat so I could compare.
The thermostat is the large brass piece. Sticking out the top is a brass cylinder that acts like a plunger. You can pull this piece out and should especially if you are trying to clean the thermostats out. The mechanism that moves as the temperature heats up is inside the brass body, so you can't see it. All you can see is its effect as it pushed the brass plunger out.
To test it, out your thermostat with the spring wrapped around the base in a pan of water upright. INstall the little brass plunger. Make sure it is pushed all the way in.
Turn on the burner. As the water heats up, you will notice the plunger will be pushed out the top of the thermostat. This action moves the baffle in the engine block and allows more cooling water into the engine.
A quick cleaning in vinegar solved my sand issue and overheat issue. Now I know how to check the stats.
Couple other observations -- the stats don't open till the water is hot in the pan. THey also don't close quickly once they cool down.
When I got my engine overheat alarm, the water exiting the engine was hot --- barely able to put my hand under it. Normal operations when I checked, the water was just warm and this was operating in 65 degree ocean.