I would first look to the radiator, is it a good aluminium core Behr in good shape or it it a copper and brass whatever? IMHO the aluminium radiators, A/C condensers all seem to work much better than their traditional counterparts, even if they do have the "cheap plastic ends". From what I've seen, the eta's have the same size radiator as the 533/535 so I would think it would be adequite. But you should have an aux fan too though. Mike W.