Oil Thermostat Question?

[Pig Farmer]

I recently notice a small leak coming from my ER oil cooler. The leak appears to be coming from the return side of the core, but it's difficult to tell if it could be the hose fitting. Since I started monitoring the leak (for about a week) I've lost maybe 2-3 oz of oil, but I also noticed that the oil cooler does not get hot at all! I assumed I had a clog somewhere in the oil cooler core or return line that was preventing the oil from flowing through the cooler. I pulled the lines and oil cooler this morning and there appears to be no blockages. Does anyone know if the thermostat is designed to close if it senses a pressure drop in the oil cooler? I'm very confused why the core is not getting hot when the oil is up to temp. Any help would be appreciated. Thanks.