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.


Paul Lamar

Hi Paul
I changed my coolant recovery system to a small pressurised overflow

tank

instead of the unpressurised original because the system had no

elasticity.

With short, very firm water pipes and small aluminium header tank

the

pressure went quickly to cap pressure on start up and overflowed to

the

recovery bottle. The overflow continued all the way to 10,000 ft. On

the way

down the pressure dropped to zero. This meant that I could not use my

low

coolant pressure alarm, and also suffered some water loss.

With the pressurised system there is no water loss and the pressure

remains

above 10psi until long after shut down. Only a small plastic bottle

half

full is required. The bottle is off a GM Camaro car.
The gauge reads about 11psi at 1,000feet. At 9,000feet it usually

reads

17psi. The cap, which is on the overflow bottle is labelled 10psi.
 I have a schreader valve to pump the system for cold testing, the

cap

releases at 11psi. cold.

Happy flying, Ian Rotary RV6A. Australia.

On  this note,  I've been wondering has anyone used a Saturn recovery
bottle?  Yes I have a Saturn, and the pressure cap is rated a 18psi.  I
believe this acts as a overflow as well as a location to monitor and
fill the coolant system.

Tom Webber

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