Hello, John Talley here with boats.net. Today I'm going to walk you through the really
simple process of replacing a thermostat and a diaphragm on a Mercury Tracker 40 horsepower.
Pretty simple to do, and what i'm actually doing right now is transferring it from an old block to
a complete engine build that we did. So let me go grab my tools and we'll dive into this project.
And what we're going to be replacing behind that cover is the diaphragm,
the thermostat, the associated o-ring gasket with it and then the outer gasket. Now like I said,
for this particular setup we're transferring it from an old block
to an engine build. Now if you want to see that happen, why don't you check out
this unit's playlist and walk you through the procedure of what it took to rebuild this block.
Now to remove it, it's really simple: you just need a 13 millimeter socket and we're going to
take off these four bolts, because all we're really after here is the cover itself, a spring,
and then the mount that the diaphragm goes on.
Now one of the telltale signs of a thermostat that's either stopped up or
not functioning at all is either a it's overheating, or b, it's not
coming up to a good running temperature and probably fouling out your spark plugs.
So that could be an indicator that your thermostat is not functioning as it should.
All right.
There's your housing, your spring, the diaphragm, and this was your old thermostat. And look at that
one. I would imagine that it was not flowing very well, because that looks pretty rough.
What we need to do is remove this end cap from the diaphragm,
take that apart, take the old diaphragm off, install the new one.
That's just a phillips head screw that's doing this, and when you start it back on,
keep in mind this is just nylon so you want to make sure you get it started in the threads and
not creating new ones. If it's got too much tension, back it off and then bring it in.
Now it's just going to be reverse of what we did to pull it apart.
Diaphragm in first. All right guys, we've got a spring in place, we're going to go ahead and
put our thermostat in the housing first. We've got our bolts in place, then, we're
going to put our gasket. I know this is a little tricky, but this is the best way to do it. Now
hold all that together... there we go.
Just bring your bolts in finger tight. Now you should be able to just push with your hand to
get it to go flush. If you can't, that means that your thermostat isn't aligned like it should be.
The trick is to have the gasket in place on top of it holding it into
the cover itself. Because if you try to do it the other way,
it's going to pinch the gasket and not seal up properly. There, we've got it.
Everything looks good, let's go ahead and tighten these down.
Now we're going to torque these to 16.5.
All right guys, there you go. That's going to wrap up this particular video. Well listen, if you need
any parts for your boat, why don't you come see us at boats.net and we can get you taken care of.
If you have any questions or comments, leave them in the section below and I'll do my best to answer
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