Oil coolers on Harley-Davidson motorcycles

Cold oil is viscous and does not lubricate as well as hot oil. For oil to lubricate properly, it must reach a certain temperature, the operating temperature. The ideal temperature is between 80° and 120°C (~175°-250°F). If the oil stays colder than 80°C, the water content cannot evaporate (oil always contains some condensation from the environment or from cold starts) and the lubricating quality decreases. If the engine oil often and for a long time gets hotter than 120°C, it loses its mechanical properties and the oil changes chemically for the worse. The only way to avoid the water content is warming-up, and the only way to avoid overheating is to use an oil cooler. To prevent the oil from remaining too cold for long with the cooler activated, a thermostat should be installed. This only opens the circuit to the cooler at oil temperatures above 80°C. If the oil remains below 90° for a longer time while the cooler is switched on, you should consider using a smaller cooler or covering your cooler partly.

No faith in thermostates?

Another control option requires a bit of manual action. In addition to the oil cooler, a bypass valve and an oil thermometer are installed. On hot days or long highway trips, you just will have to remember to check the oil temperature during a cigarette break and open the valve if necessary.