Harley-Davidson's Hydra Glide?

Liquid-cooled big twins, sort of

Here’s one Harley-Davidson engineering experiment you can expect to enter production soon. Recent patent applications reveal the Milwaukee manufacturer plans to partially liquid-cool at least some of its air-cooled V-twins. Don’t expect an all-new engine, however. In typical H-D fashion, engineers have managed to update the Big Twin engine without changing the outside appearance at all. A simple water passage routes coolant through the cylinder head and then down to a pair of small, fan-cooled radiators concealed in crashbar-mounted leg guards. A small electric water pump, mounted between the frame rails, enables circulation. It’s a simple, subtle solution, but in a world of ever-increasing emissions, economy and performance demands, this is another important step in extending the life of Harley’s traditional V-twins.

Water-cooled cylinder heads are similar in design to the oil-cooled heads presently used on the XR1200. Using water offers more efficient cooling without disturbing the existing oil system.