I'm intrigued by this discussion (although I don't have a problem with my Roadster radiator as far as I know), because I have previously owned TVRs which featured a "swirl tank" (or "swirl pot"). This article explains:
https://www.merlinmotorsport.co.uk/...system-header-tanks-in-your-race-car-323I recall there was some discussion among TVR owners as to which of the caps should be "pressure relief" type, and which simply plain. In my last TVR, an S3, also with a Ford V6 (2.9) engine, I had a swirl pot with a pressure-cap above the thermostat. The overflow just had a cap, as the level never reached more than about half. This is probably all basic stuff for somebody who knows more than me about Morgan cooling systems, and will probably be able to explain which of our cars if any have swirl pots.
![[Linked Image]](https://www.tm-img.com/images/2022/05/26/S3-engine-bay-showing-swirl-pot-and-overflow-with-caps-2.jpg)
