Hobbies Cars & Motorcycles 6 Things You Should Know About Liquid Cooled 2014 Harley-Davidsons Share PINTEREST Email Print Cars & Motorcycles Motorcycles Buying & Selling Motorcycle History Restoration & Repairs Cars Used Cars SUVs Trucks ATVs & Off Road Public Transportation By Basem Wasef Basem Wasef is the author of "Legendary Motorcycles" and "Legendary Race Cars." His work has appeared in Autoblog, Men's Journal, Robb Report, and Wired. our editorial process Basem Wasef Updated December 25, 2018 Harley-Davidson dropped a bomb on the motorcycle world by announcing that several non-V-Rod bikes in their 2014 lineup will feature liquid-cooled cylinder heads for the first time in 110 years. But what does liquid cooling really mean for the Motor Company? The New Twin-Cooled Engines Are Still Primarily Oil and Air Cooled The Twin-Cooled High Output Twin Cam 103 and the Screamin' Eagle Twin-Cooled Twin Cam 110 incorporate two discreet radiators in the fairing and a centrally positioned water pump that cool the cylinder heads. Harley-Davidson Some people might assume that the term “liquid-cooled” refers to a full-blown, water-cooled engine, but Harley’s so-called Twin-Cooled power plants use both oil and water for thermal relief, applying coolant only to the cylinder heads (which leaves the engine block cooled by oil and air), and focuses the cooling effort towards the hottest part of the heads: the exhaust valves. The system is similar to BMW’s R1200GS which also focuses its liquid cooling to the heads, and even shares the same terminology: BMW calls their setup “Precision Cooling,” and Harley says their system uses a “Precision Liquid Cooling Strategy.” Service Intervals Remain the Same The Ultra Limited on the road. Tom Riles Cooling the cylinder heads with liquid has no effect on service interval: Harleys with equivalent Twin-Cooled and standard engines require service after the first 1,000 miles, and 5,000 miles thereafter. Incidentally, the new engines use the same coolant blend as the V-Rod, a 50/50 premix that uses long life coolant. Unlike oil and air-cooled engines which adjust timing to avoid spark knock as temperatures increase, Twin-Cooled engines retain the same timing. Improved Performance and Comfort The Ultra Limited's radiators are hidden inside each of the fairings flanking the forks. Tom Riles You may have heard that Harley has boosted engine output between 5 and 7 percent, which might make you think those gains are all due to liquid-cooled heads. But that’s not entirely accurate. The engine improvements which came with Project Rushmore include new cam profiles with higher lift and duration, which aids overall performance. But both the standard and Twin-Cooled engines see the performance gains. What’s better about the Twin-Cooled setup is that it maintains those gains more effectively under thermal loads, when ambient temperatures rise and the engine is working under more duress. The net goal to the rider isn’t really about performance; it’s more about avoiding crotch-melting temperatures and increasing the comfort of the ride. Twin-Cooled Engines Still Get Hot Liquid-cooled heads reduce temperatures at the upper parts of the engine, but the lower sections can still heat up. Brian J. Nelson My test ride aboard the new Twin-Cooled FLHTK Ultra Limited involved long distance riding in ambient temperatures that reached the upper 80s. While the bike heated up noticeably less than its oil and air-cooled counterpart, the lower portions—namely, the crankcase area with the exhaust pipes on the right and the primary drive piece on the left—still got hot enough for some discomfort, which I’ll discuss in more detail in an upcoming review. Don’t get me wrong: the Twin-Cooled engine was considerably more comfortable thanks to its liquid-cooled heads, but other parts of the engine still managed to heat up my legs and lower thighs. The Cooling Bits Are Hard to Spot From just the right angle, coolant hoses can be seen between the cylinder heads and fuel tank. Basem Wasef At a glance, you’d be hard pressed to differentiate a Twin-Cooled Harley from an old school, oil, and air-cooled example. Because the radiators are discreetly tucked into the twin fairings just ahead of the rider’s legs, the coolant hoses are sandwiched between the tops of the cylinder heads and the fuel tank, and the water pump is dropped well below the leading edge of the bike’s down tubes, the system tucks away neatly, all but disappearing thanks to convenient packaging constraints. If anything, Harley worked to visually differentiate Twin-Cooled engines by giving them unique, rounded air cleaner covers. If Harley-Davidson chooses to add liquid-cooled heads to bikes outside of the Ultra family, engineers will be faced with a considerably more challenging task of hiding the system’s radiators. Twin Cooling Is an Experiment This rounded air cleaner cover distinguishes Twin-Cooled Harley engines. Basem Wasef Contrary to popular belief, Harley-Davidson didn’t have to go with liquid-cooled heads because of regulatory constraints or government certification requirements. The system was designed based on customer feedback gleaned from Project Rushmore, and Harley left the door open to either expand it throughout the lineup or eliminate it if customers revolt.