I suspect my outboard engine thermostat doesn’t work properly so I’ve taken it out to check it, visually it doesn’t look too good, it’s stuck open with crud so obviously won’t work properly

Gave it a clean up, hooked out the crud and wire brushed it

Gave it a soak to descale, I use Kilrock Big K as it works for me

When the fizzing stopped pulled it out

Gave it a rinse under fresh water and popped it in the freezer for a few minutes, still stuck open so this one is a write-off

Want to test new thermostat before fitting to make sure it works OK, this is the info from the servicing manual.

Valve lift is to be in the range of 48-52⁰c So I need a 50⁰ thermostat as the thermostats are rated by the temperature at which they begin to open.

The thermostat rating is stamped on the thermostat, either on the end of the bulb

Or on the “Legs”

Take my 50⁰ thermostat, first of all make sure that at ambient temperature it’s fully closed

Now to check the thermostat, you will need a jug that can hold warm water, some way of suspending the thermostat (You can just tie a piece of string around it), A thermometer to measure the water temperature and some way of measuring the open gap.

Suspend the thermostat in water and raise the water temperature to the opening temperature (for this one we know it’s 48-52⁰c) and raise the water temperature, at the opening temperature you should see the thermostat begin to open.

Continue increasing the temperature to the fully open temperature (for this one 60⁰c) at which point you need to check how much the thermostat has opened, the specifications above said more than 3mm so I’m using the shank of a 3mm drill as a gauge

And then immerse the thermostat in cold water again to make sure it shuts fully

You have now carried out a check of your outboard engine thermostat, you know it opens when it should, opens as far as it should and closes when it should. Job done….