Reply to "Question about expansion tank cap"

Mike,

Assuming the cooling system is unmodified in terms of how it operates, assuming there's no "gotchas" to bite me on the arse, the expansion tank cap should NOT be sealed tight, it should be vented to atmosphere. Therefore the expansion tank actually operates as a simple recovery tank.

To be technically correct an expansion tank is a recovery tank that operates under pressure. Ford/De Tomaso literature refers to the tank as an expansion tank incorrectly.

Of course the whole concept of a coolant recovery tank was fairly new to the US auto industry in 1971. When Ford began equipping production cars with recovery tanks they were made of plastic and none of them had a pressure cap. Expansion tanks were European contrivances in that time frame.

The concept of a swirl tank paired with a header tank was foreign to everyone at Ford except those who had worked in the Indianapolis or GT40 racing projects. I have been fairly vocal about the fact that I suspect those two tanks were originally configured as a swirl tank and header tank. Whether or not that is true is a moot point in terms of functionality. If anybody wants the cooling system to automatically remove air from the radiator and isolate that air from the cooling system, that is how the system MUST be reconfigured. It is very easy to do.