MDR Industries Billet Expansion Tank Honda CTR FL5 / FK8 & Acura Type S DE5MDR's direct replacement upgrade billet expansion is CNC machined out of 6061 T6 aluminum alloy, TIG welded, and anodized. This was created to address the issue of leaks at the seams from the factory plastic expansion tank cracking due to continuous heat and pressure cycling. This billet expansion tank is a direct factory replacement. Size and shape are identical to the factory plastic unit while utilizing all factory mounting location and hoses.