Responding to Bill Jepson's comments.  I wasn't considering the coolant
recovery bottle as a header tank.  Why would you need a header tank?  Cars
don't use them anymore.  All of the air should be purged from the system
(except for the recovery bottle).  Years ago, header tanks contained some
air that buffered the expansion of the coolant.  Didn't recovery bottles
replace the expansion tank?   Is there any advantage to maintain some
pressure in the recovery tank (5 to 15 lbs)?

Del, The reason for using a header tank is simple. We can rarely place our filler
cap on the radiator and have it be the high point in the system. Several modern
auto layouts use a header tank when using a angled radiator. I believe the
Corvette is an example. It doesn't have to be big. I believe Al is using a simple
2" pipe extended to the high point.
The answer to the second question is yes, There are several systems using a
pressure cap on the recovery tank also. This should help return the water to the
engine as the radiators cool the water enough to decrease it's volume. At least
that is the theory.
Bill Jepson

 
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