I bought the Stant #10231 radiator cap yesterday. The description shows:
""Designed to function on open cooling systems and overflow reservoir type systems".

It looks to be a dual purpose cap.

www.sportinggoodsoutdoor.com/p/detail/B000B8N3GE/Stant-10231-Radiator-Cap-16-PSI-Vented.html


1970 YO7 A66 [Canadian Export] F8 Challenger
340 (Currently in shop for stroker assy.)