That isn't a zero pressure system.... It is a waterless, but not zero pressure as it is still closed with a 1.4 bar cap. (which is about 20 psi) The pressure in a cooling system is from the expansion rate of the metal in the engine, not from coolant boiling. I have not yet seen a "no pressure system" in my life, not even on my old '69 F250. Basically if it has a sealing cap it has pressure when above room temp.



**edit** I have seen a no pressure system, and it is waterless as well. Volkswagen beetle.

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