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M8 extra air cooling.


It is striking that the newer touring models get incredibly hot and that this is also clearly noticeable when you ride the motorcycle. There are quite a few reasons why the engines have gotten hotter over the years. First of all, Harley sticks to air cooling, which means that if you stand still with the engine running, or are cruising quietly, the temperature rises quickly. Another reason is that due to emissions, the engines are delivered with an increasingly lean mixture, which makes for a much hotter engine block. Fuel cools the engine and the less fuel in relation to the air, the less it cools.


Harley actually had to go to the 4-valve head and a flat combustion chamber, because this shape is much more efficient and gives less chance of detonation or knocking. This allowed the compression to go up, and the block accepted the much poorer petrol injection without breaking down. Simply put, the M8 has been developed to run even poorer. The additional drawback is the heat. There are 2 parts that get the hottest and those are the exhaust valves and the pistons. On the M8 models an extra oil channel is made around the exhaust valve, and this oil goes through an oil cooler at the front of the engine. To provide extra cooling of the pistons, jets are mounted under the pistons in the crankcase, which spray oil from below into the piston to cool it. The Twin Cam already had this.


There is also a catalytic converter in the exhaust as standard, but the additional effect of a cat is that it becomes very hot due to the hot exhaust gases. This can clearly be felt on the baggers when you sit on the back, your right foot is just above it. The rear front corner is also a real ball warmer at the traffic light. You also see everyone driving with those plastic caps and it is clear why.


Now the current fashion image does not really cooperate. Everything black, gaiters for the engine, front spoilers and a bigger and thicker front wheel with a huge fender is all the bomb. For an air-cooled engine, this is a thing. Because if there is no wind blowing past the cylinders and heads, and your oil cooler is hidden behind a huge wheel, then somewhere not quite right.



What can you do to make the engine run cooler. First of all, adjusting the injection is a good way to lower the temperature. Nobody is perfect, so the injection of a Harley is never the most perfect for every bike. Especially if the owner spoils his engine with an open air filter and exhausts with a bit more noise, this will result in an even poorer mixture, so a good mapping adjusted on a bench ensures a less hot engine.


A second option is to mount an oil cooler with an electric fan on it. Harley calls it the Oil Cooler Fan Assist Module. The engine management already measures the temperature of the oil and controls the fan when the temperature goes to the high side. Assembly is fairly simple and you don't have to pull any wires, Harley has already prepared everything. Plug it in and activate it in the BCM (Board command module) and it works. The cooler is supplied by Harley or by Zippers, Thundermax.

A third option is a Harley electric fan that sucks the hot air away from the rear exhaust bend and blows it down. Again, all wires with plugs are already prepared and it seems that Harley has already realized that the temperatures are rising to much too high values, but now you have some extras to pay for it, but good. There is also a switch in the front of your cockpit and you can turn it on, off and on automatic. Also plug and play and activate in the BCM.


The Oil Cooler with Electric Fan is Harley's 62700204 and works on all 2017 and later air-cooled M8 touring models.


Zippers also supplies the cooler zpn 723233. The coolers are around 350 euros


The Coolflow Fan Kit 26800120 is from Harley and costs just under 400 euros

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