8 Pros and Cons of the Water Cooled Rushmore and Milwaukee 8 Bikes
Water cooling is the latest fad in engine technology that Harley-Davidson is flirting with, like fuel injection, but chances are it will never catch on. Here are some of the reasons for and against getting a touring bike with the Twin-Cooled Twin Cam or new Milwaukee 8 motor.
1. Pro - Engine Oil Stays Cooler
On all of the big twins without the Twin-Cooled system the lubricating oil is pressed into double duty as a means of cooling the hottest parts of the motor as well as lubricating the moving parts. That means, when you most need lubrication and cushioning in the engine, when everything is running hottest, the oil is going to be at its thinnest and least effective. Harley equips the air/oil cooled touring bikes with an extra quantity of oil and a bigger pump, but it is only 1/2 a quart more. Whether you go with water cooling or oil, the new Milwaukee 8 or the Rushmore Twin Cam, special passages around the exhaust valves help keep the hottest part of the motor cool. Shown in blue are the water passages on the new motor.
2. Con - Additional Fluids to Leak
New Harley-Davidsons don't leak oil anymore, but it took them years of R & D to get to this point. After many years and many miles, even the new ones do start to get less than perfect even in the 21st century. The Twin-Cooled motors add an entire separate circulatory system of hoses, lines, radiators, thermostats, and pumps to flow the antifreeze/coolant around. Chances are your bike won't leak coolant, but without the liquid cooled motor it is 100% certain because there is no coolant to leak.
3. Pro - Cooler Legs
If you look around on the forums, you will find reports by owners of Twin-Cooled Rushmore bikes, and the new 8, who have also ridden traditional air/oil cooled versions and report the comfort level is much improved. Even in cool temperatures, a high performance big twin can roast your legs in just a few minutes of stop and go traffic. With the addition of liquid cooling they claim to be able to ride in the worst summer heat with their feet and legs only getting slightly warm, but never uncomfortable or painful, the way they sometimes get on touring bikes with lowers. The mini radiators tucked into the lowers are vented by a fan to the side and away from your feet.
4. Con - No Lower Storage or Speakers
For years the upper part of the fairing lowers was empty and could be used as a lockable storage area or space to install another set of speakers. The liquid cooling part of the Twin-Cooled motor takes this space and uses it for the coolant overflow bottle, fan, and vent area. If you are one of those bagger riders who needs a dozen speakers blasting music at you, you just lost one of the best places to install them.
5. Pro - Full Power Even in Summer Heat
Touring bikes are made to take you and a passenger, and your stuff, cross country, but when modern air cooled bikes start to run hot under load, the computer will adjust fuel and timing to keep them cool and within emission parameters. That means, you will lose some of your power in the name of smog and motor wear and tear. The Twin-Cooled motors don't have that problem, because when they get hot, the fans go on and the system circulates more coolant instead. This is even better news if you plan on any modifications that will increase the output of the motor, because power makes heat and it has to go somewhere.
6. Con - You Have to Run Lowers
If you want to have it your way, and run a stripped down bagger but still employ the Twin-Cooled motor, you can't. They say it takes all kinds, and if you are convinced of the advantages of liquid cooling for your Harley, you had better want a full dress touring bike with lower fairing. Other companies have built liquid cooled V-twins, and hidden a radiator between the frame down tubes, but so far Harley is convinced most of their bikes can do without.
7. Pro - Less Engine Wear
An engine that is cooler will wear less. Metal expands with heat, and if you get it hot enough, the pistons get too big for the cylinders and the whole motor stops. Unless something is seriously wrong with your bike that never happens anymore on modern fuel injected Harleys. However, the the Twin-Cooled bikes should run at a more uniform temperature, so there should be less expanding and contracting, less wear, and less chances for leaks to develop.
8. Con - It's Scary and New
Why do modern bikes need liquid cooling? Weren't they just fine with a bunch of fins and air cooling? And what is with the fuel injection, and the computer that runs it and every other aspect of the bike? Why not just have the foolproof magneto ignition and a Linkert carb? Why 2 cams? Why 8 valves? Why 6 speeds? Why electric start? These modern bikes are like a Cadillac on 2 wheels, and weigh about as much. If it ain't broke, why mess with it?
For help fixing and maintaining your touring bike, Softail, Dyna, Sportster or other Harley, click over to the How-To section of the HDForums.
