The back cylinder on an air cooled V-twin can generate a lot of heat when
the bike isn’t moving.
In the interest of full disclosure, let’s get this out of the way. I’m not a big Harley fan. I’m not a Harley basher either. At least not in the usual sense. I don’t think they’re incompetent. I don’t think modern Harleys are junk or they are incapable of good engineering. I do think image and style are more important in the company mindset, and they intentionally and frequently make design decisions on that basis. Their engineers, far from being incapable, are masters of finding ways around intentional design limitations.
A case in point. I’ve only recently become aware of a change in Harley engines beginning in 2009 called EITMS, or Engine Idle Temperature Management System. This system goes on Harley Davidson touring bikes. Harleys are infamous for the amount of heat their engines produce, especially when road conditions or traffic cause a lot of stopping. If you can’t keep air flowing over an air-cooled engine, it’s going to get hot.
All of my motorcycles have had some variation of liquid cooling. Both of my Hondas use water and my Victory had an oil cooler. When my bikes are stopped for some reason, oil or water continues to shuttle heat to a radiator where it is cooled. In both cases a fan is able to keep an adequate amount of air flow over heat dissipating fins, whether or not the bike is moving.
But Harley style sensibilities have declared radiators verboten. Apparently broiling your gizzard is considered cool by someone high up in the Harley hierarchy. So Harley engineers had to figure out how to keep the inevitable heat of an internal combustion engine from cooking the rider, or seizing up the engine during times of reduced air flow. My hat is off to them. It’s an ingenious solution, but to a ridiculous problem.
EITMS shuts down fuel to the back cylinder when the engine is idling and when engine temperature reaches some pre-set level. The piston and valves still operate, turning the back cylinder into an air pump that, hopefully, pumps heat away from the motor. I’m sure that it is comparatively cool. Compared to the surface of the sun, the heart of a thermonuclear explosion or a regular Harley engine, it is probably quite cool. Probably not so much when compared with any other motorcycle engine equipped with a radiator.
And then there’s the “I” in that acronym. Idling. This cooling scheme won’t be much help hauling that hog slowly up a hill. It’s an immutable law of physics that producing energy produces heat. The more power an engine produces the more heat you’re going to have to get rid of. Bugatti engineers understood this when they put 16 radiators in the Veyron.
I don’t doubt for a second Harley understands this. As I’ve said before, their engineers are quite capable and intelligent. Harley upper management has decided that the “style” of an air-cooled engine is more valuable than the efficiency of a radiator. And the motorcycle riding public seems to agree with them. According to a July 20 article in Manufacturing.net, “Harley now expects to ship between 228,000 and 235,000 new bikes worldwide this year, representing an increase of 8 percent to 12 percent over 2010.”
I’m clearly in the minority here. As impressive as the EITMS is, I can’t help thinking that a radiator would be a lot more efficient and reliable.
－ Guy Wheatley