Tested: Radium Engineering Coolant Expansion Tank


Radium Engineering’s Coolant Tank Design

Constructed of Billet 6061 Aluminum and powdercoated for durability and good looks, Radium Engineering designed their Coolant Expansion Tank with severe duty in mind. Its design features the three standard ports in a novel configuration: the radiator vent and return line are -10AN ORB (O-Ring Boss) ports on the bottom of the tank, and the steam line from the engine leads to the -6AN ORB port on the top.

The top steam line port is designed for improved deaeration of coolant. It tangentially leads to a circular swirl chamber. The coolant leaving the engine through this line is swirled at a high rate of speed, and this centripetal acceleration efficiently spins any air or steam bubbles away from the coolant before returning the now deaerated coolant to the coolant system. Passages machined into the top and bottom of the swirl chamber allow coolant to mix and provide deaeration from both the radiator vent and steam lines.


This CFD analysis shows how coolant entering the circular chamber from the tangential port is swirled around, throwing air and steam bubbles off from centripetal acceleration before returning back to the cooling system.  Source: Radium Engineering

The compact design of Radium’s Coolant Expansion Tank allows it to be mounted virtually anywhere in an engine bay, freeing up space for forced-induction piping or allowing V-mount or rear-mounted radiators. The oversized AN ORB fittings allow easy interfacing or conversion to braided stainless lines.

Radium’s Coolant Expansion Tank is available by itself for use in custom applications. Radium also has kits available for the ‘11+ Ford Mustang (S197 and S550), Ford Focus ST and Lotus Elise/Exige.  These kits include the universal tank, an application-specific bracket, and the AN fittings and hoses required for installation.

If installing Radium’s tank in an application that doesn’t normally have an expansion tank (for instance: ‘90s Hondas), simply seal off the stock radiator cap and install Radium’s expansion tank in a suitable location.


Assembling and Installing Radium Engineering’s Coolant Expansion Tank

Now, onto the assembly!

Radium’s Mustang kit includes the tank, an application-specific bracket, and all of the needed hoses and AN fittings to install it. Note that the pressure cap is sold separately. Several different pressures are available, so be sure to check the pressure for your application.  Pay no attention to the cluttered workbench!


CNC-machined and finished in a beautiful, black powdercoat, Radium’s Coolant Expansion Tank will dress up any engine bay.


You can actually see the machining marks inside the tank’s halves. The top half is on the right; you can see how the upper steam line port leads into the swirl chamber. 


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