Coolant Expansion Tank Kit, Exige, OEM Location Radiator Cap, Type-A, 1.3Bar, 18.9psi

The Radium Coolant Expansion Swirl Tank features three ports that use -6AN male adapters (not tapered pipe threads) for a positive seal. The main tank is a 2-piece design constructed of billet aluminum. 

The two halves are bolted together along with a CNC billet aluminum cap receiver which mates to any standard 32mm "Type-A" style pressure cap.

The Radium Engineering tank also has a swirl feature, as shown. Pressurized coolant is sent into the vortex chamber's inlet tangentially and accelerated to a high rate of rotation. This is an old hot rod trick to help aid in deaerating the system.

The S2 Lotus Elise, Lotus Exige, and Lotus 2-Eleven comes standard with a Denso coolant expansion tank. This is the same plastic tank that is found in the Toyota 2ZZ-GE equipped vehicles. For fitment, Lotus designed a complex bracket that incorporates a mount for the electric hot-soak water pump. There has been cases reported where the Denso tank has failed and owners have found that new replacements are quite expensive. Radium has simplied the Lotus design by making two separate mounts and further improved it using a robust aluminum tank and adapting the factory hoses to -6AN fittings.