Quote Originally Posted by Greg Amy View Post
Why?

The intent of Bob's Mustang's overflow tank is to bleed excess liquid coolant overboard due to expansion, because there is no expansion area inside the cooling system. Bob's V-dub, on the other hand, is a fully enclosed system, built with expansion area internally (in the properly-named "expansion tank"), thus is not intended to blow off liquid at any time. Unlike on his Mustang, his V-dub's "radiator cap" (actually, the "expansion tank cap") is not intended to allow air/liquid to escape ever except as a point of last resort to keep other parts from failing (such as a radiator hose).

To require a "catch can" in such a system is analogous to requiring a "catch can" for all other parts of the system that may fail (such as a radiator hose catch can).

But, if the rule is enforced to the letter of the law, then Bob's system is, in fact, illegal because it does not actually have the required "catch can". And to require one would negate the functions of the system (actually - to the letter of the rules if you want to get picky - it doesn't say that catch can has to be attached to the cooling system...)
I would have to assume the purpose of the proposed rule is to help keep coolant off the racing surface. To that end, the fact that the V-dub expansion tank is not intended to allow liquid to escape, will be of little consequence when something goes wrong. It's no different than the '66 Mustang, it just takes another lap or two for it to happen. And possibly even less, if the system was inadvertently overfilled.