Replacing Thermo-stats on the Mercury Outboard

Part of our motivation to get out fishing this weekend - in spite of the rain - was that we've been working alot on the outboard, and wanted to put some time and gas through it to make sure its back together reasonably well!

As you may remember, we've been plagued with the motor running alittle too hot - especially at lower RPMs. Earlier, we replaced the water impeller, and now we are taking care of the thermostats. Fortunately, they are located at an easy-to-access spot on top of the motor, as shown.

Two bolts and they are both easy to take out.

We popped them both out, cleaned them off, and tested them by putting them in hot water, to confirm they pop open at the expected temperature.

There was some sand and grit... as we suspected. They both worked as we expected, too.

With the 'stats out, we flushed water through the motor for a while.

Easy to do, though not sure how effective it proved to be...

The real problem is likely to be the Poppet valve - a simple valve that lets water pressure build up in the motor before openning to release the pressure. Its at the base of the motor and so will take more to replace it, but it would explain the motor's heating up. It is likely clogged with sand from camping on the island this fall during fall Chinook...

So, we took it out and sturgeon fished - keeping a close eye on the motor temp gauge!

The motor ran great - strong and clean. Plenty of water out of the "tell-tale" vent on the motor, too.

But... at lower RPMs and boat speed the motor did heat up higher than it should have. Never red-lined, but did get hotter than we like.

We ran it hard-n-fast for 15 miles or so... next step, fix the Poppet valve. Stay tuned...