What Is the Best Oil for a Harley Davidson?by Don Bowman
You can't use just any oil for a Harley Davidson--it has to be a specific oil, as the Harley is not water cooled. Therefore, the oil is used to help keep the engine cool. Harley makes a specific oil that is not available at most auto parts stores. The weight of the oil depends on the air temperature. It helps to understand that an air-cooled motorcycle engine is different in many ways than a four-stroke automobile engine, as it is air-cooled and uses no auxiliary fans. In one of the few automobile engines that utilizes an air-cooled engine, there is always a fan used to direct the air and heat down and away from the cylinders and the cylinder heads. This aids in the cooling process for the most part when the vehicle has no forward motion.
Motorcycles that are air-cooled use a much higher viscosity than those that are water cooled. Harley Davidson recommends that the oil be changed at the first 500 miles and then every 2500 thereafter. For climate temperatures of 40 degrees and below, the correct oil is HD for Harley Davidson grade 58 weight. For temperatures of 40 degrees and up: HD grade 75 weight. For temperatures of 90 degrees and up: HD grade 105 weight.
Without the use of the correct oil, the engine will not be able to maintain oil pressure under all circumstances, and this will cause severe wear in a short period of time. Even the correct oil must be changed as to its viscosity, depending on the climate. Motorcycle oil in not used in automobiles and vise versa.
It is advantageous to understand the air-cooled motorcycle engine and the demand that is made upon the oil in all-weather conditions. Without the aid of a cooling fan, the temperatures absorbed by the oil are far higher and fluctuate far more than that of a car. Understanding this, it is obvious that the oil commensurate to this environment is necessary to maintain the proper lubrication requirements for this heat range. This knowledge will help to extend the life of the engine.
The Harley Davidson oil has a far higher viscosity or weight than an automobile because as oil gets hotter, it gets thinner. A common car oil is 5 W30. This allows the oil in hot temperatures to go no lower than five-weight and no thicker in cold temperatures to 30-weight. This would never do in a Harley, as the oil would be so thin the bearings would wear out in no time. Harley needs heavy oil since the engine always runs warm.
To receive the benefits from using the right oil, it must always be changed in a timely manner. If seasonal changes or changes in temperature are anticipated, these different weights should be kept in mind for continued performance. Always change the oil filter along with the oil.