jdrin wrote:
I'd just changed to an expansion tank type setup, and part of that was getting a cap let the coolant expand... I probably should do away with that setup.
If you have installed an expansion tank then it must be fitted with a matching spring loaded expansion cap. With this setup the radiator itself has a non-expansion cap which seals the radiator. Basically the expansion tank becomes part of the radiator assembly as it's connected to the radiator by what was previously the overflow tube. Coolant flows freely from the radiator along the tube to and from the expansion tank.
You can see the two basic types of cap in this Minisport advert. They call the non-expansion cap the "flat type" or "recovery cap".
https://minisport.com.au/search/?q=radiator+capAssume you are aware that there are two types of expansion caps? One is for a short neck radiator and the other for a long neck. If you fit a short neck cap to a long neck radiator the cap won't seal and water will just gush out the overflow tube when heated.
I support what others have been intimating that the standard Mini cooling system with clean and clear engine and radiator galleries, effective fan and water pump and suitable coolant should be sufficient in most conditions.
