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V-twin Tech: Sweltering V-twins

Rider Magazine
June 23, 2008
Filed under Rider Magazine Blog

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I have received some emails that lead me to believe there is some confusion about a Twin Cam’s running temperature. I would like to straighten things out.

Normal Harley engine-oil temperatures ought to be between 180 and 220 degrees fahrenheit. This is the range most engine and oil manufacturers recommend. Harley, since the first Evo Big Twin, has done a superb job of maintaining these normal oil temperatures.

Temperatures lower than 180 may not evaporate water from the oil in a reasonable time. Remember that water is the majority by-product of combustion. Some of it finds its way into the crankcase on the oil side of the pistons, especially when the engine is cold. A dozen miles at 180 degrees fahrenheit pretty much dries the oil.

Higher oil temperatures—especially above 240-260 degrees—greatly accelerates petroleum-oil degradation. The oil oxidation rate increases with temperature, and 300-degree oil becomes useless “gunk” in a very short time.

High-quality synthetic oils, such as Harley Syntec or Mobil 1, withstand much higher temperatures without losing their ability to protect your engine’s moving parts. I know that Red Line Synthetic racing oil continues to lubricate normally at 400 degrees.

I have used oil coolers on Harleys. Most of the time they were not needed and I either covered or removed them. However, there are circumstances that may call for some extra cooling. For example, heavy touring bikes making long climbs on hot days, or being ridden in low-speed parades, can overheat oil. Road racers going very fast on a hot day might run oil temps above 240 degrees.

Canyon racers (I used to be one) can have as much of an oil-temperature problem as the mountain-climbing bagger pilot. Both need an unusual amount of power at relatively low speeds where cooling is reduced. My experience is that road racers are less likely to have an oil-temperature problem than canyon riders simply because they are going much faster and the cooling is better.

Unless your engine’s oil temperature consistently exceeds 240 degrees, I wouldn’t bother with an oil cooler. If you do need one, buy it from Harley-Davidson. I have tested a number of oil coolers and most of them didn’t work very well. The Harley coolers do and they have been tested to withstand all those Milwaukee power pulses that we know and love.

One more thing. As we all know, the rear cylinder of Twin Cams, especially the TC96 and 103 engines, radiates a lot of heat on the rider’s right leg. This does not mean that there is a problem with overheating. These engines were designed to handle these temperatures. The only problem is that it feels so hot! So do not judge an engine’s running temperature by the heat you feel coming from the engine—use an oil-temperature gauge.

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