Where is the best place in the circuit for a swirl pot?
Prior to the inlet side of the pump or on the exit side of the block?
Looking at the general layout of our firewall aft arrangement, it would seem
that a swirl pot at the top of the firewall might be ideal. This would also
indicate that a simple elbow pointing to the inlet of the swirl pot could be
welded to the top of the water pump without a filler cap on the pump outlet.
...Chrissi

That sounds about right to me. However don't forget the fluid 
must then go through the rad so what ever happened in the swirl
pot is now changed. Therefore swirl pots or pressure tanks
are now rarely used in cars or trucks. 

I think what is far more important is to vent the block anywhere 
vapor could form steam pockets to the highest point in the system 
just below the pressure cap. If a swirl pot is used that should
be the place the vents are plumbed to.

Use a non pressurized coolant recovery tank as large as possible. 
At least a gallon. This will allow you to level out and recover any
puked coolant that may have happened on climb out.

Do not underestimate the importance of the pressure cap.
This is a flight critical item. One should use the highest
quality possible. Each cap has two valves. One; a pressure
activated valve that dumps the pressure at some value
say 15 or 20 psi above atmospheric and two; another one-way
valve that allows coolant to be drawn back into the
block from the non pressurized coolant recovery 
tank when the system cools down a bit. This happens when
the fluid in the block contracts and the engine block contracts. 

The interesting thing here is the absolute pressure in 
the system at sea level is 15 plus what ever the pressure 
cap is or about 35 psi. Assuming a 20 psi pressure cap is used.
The absolute pressure is down to about 30 psi when at
high  altitude and atmospheric pressure is only 10 psi.

I find it real strange that Continental decided to use a 3/4 full, 
two gallon pressurized expansion tank in their system without a 
coolant recovery type pressure cap. I am still trying to figure out why :-)
When that tank pukes coolant it pukes it overboard never to
be recovered. They also pay a huge weight penalty for this system
as the tank is heavy wall to withstand the pressure and it holds
about a gallon and a half of coolant or about 12 pounds right
there.

BTW IMHO a better place for the coolant pump is down 
low. We of course are stuck with where it is. Some of the 
more recent engine designs have put the coolant pump at the 
bottom of the engine. This puts a bit more pressure on the 
inlet side of the pump.
 
Paul Lamar
 
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