Do you need a special type of radiator cap for the system to function?

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Rick Dorion
69 RS Conv,355,M20,4.10's

May not be special but yes it has two rubber seals instead of one.

Brian

Virtually all cars built since the 40's use a cap with a pressure/vacuum valve in them; the pressure valve allows coolant to bypass the primary seal and exit via the nipple to the recovery tank (on recovery system cars)when the pressure created by the overheated coolant exceeds the cap's rating, and the vacuum valve allows coolant to be drawn back into the radiator through the same nipple from the coolant recovery tank as the engine cools and a vacuum is created in the cooling system. Pre-recovery system cars just allowed hot coolant to be puked out through the nipple and overflow hose. Caps haven't changed for years except for increased pressure ratings.

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JohnZ
'69 Z28 Fathom Green

Rick, when you come up, take a look at the custom coolant system that I installed.