Harley Davidson Forums - Stock oil cooler open/close temps?

The answer to your question is a little tricky. The OEM oil thermostat starts to move at 185*, fully stroked, or fully open at 195*, but that is not 195* oil pan temperature. That is 195* where the oil contacts the thermostat up in the sandwich adapter at the oil filter. As the oil travels through the circuit a lot of heat is shed between the pan and where the oil actually contacts and activates the thermostat. Depending on conditions, the pan temp can be over 220F before the thermostat is fully open. Like many things Harley, the engineering department phoned this one in when the Twin Cam motor came along. All predecessor motors filtered the oil after it cycled through the engine, so the oil was actually hotter at the point that it comesin contact with the thermostat, the oil in the pan was cooler than 195F whenthe stat was fully open, so it was a pretty good functional match and one ofthe reasons pre-Twin Cam engines had lower oil temps. Then the new design TwinCam came along and the oiling circuit changed considerably by filtering the oil before it cycles through the motor, so now the pan temp is much hotter when the oil is 195F at the point where it contacts the stat, because the oil is at its hottest coming out of the engine and dumping back into the pan, in short a poor functional match for the TCs. This is an observation I captured a few years back with my multi point oil gauge and led me to the discovery that a simple change to a lower stat temp will actually lower the oil pan temp, contrary to the belief of some of the industry leaders. It’s kind of a difficult concept to visualize and understand but the same OEM stat for earlier engines is still in use and it is not a good match for TCs. I now offer these low temp stats at a very reasonable price, considering what they do temperature wise. A lot of Tstat info on my website http://www.wardspartswerks.com/thermostats.html.