Yes, I just did a rebuild on a 1993 - 3 cylinder 90 , and it too used the
poppet valve approach. A lot of the older stuff I work on has no thermostat
or poppet. The cooling flow is the cooling flow, and at high rpm's the pump
just can't push more water than the block will pass.

On my late 80's 115, the water comes in, fills the exhaust plates and then
spills over into the top of the block area. The block "top fills" from the
bottom up. When the water gets to the top of #1, the peeing starts.
Amazingly, this takes only about 10 seconds or less.

As a quick side note, I advise anyone running an earlier Merc inline 6 to
plug off the hole where the pee hose goes (with a plastic plug) and to move
the elbow fitting to the very top of the block over #1.

Mercury *finally* did this very late in production. It cures two problems:
It becomes impossible to get an air pocket up in the top, and you won't get
a "pee reading" unless the block is truely full to the very top.

-W

"Ken" wrote in message
...
For a pressure controlled system Merc uses a spring loaded poppet valve.
When pump pressure comes up the poppet is pushed open and allows for
greater
water flow. The thermo itself just doesn't flow enough water to keep
things
cool at WOT.