I do know the cooler has to be after the bypass valve for cold weather startup and driving, unless the coolers max pressure is far beyond what pressure the transmission produces. There again, it’s been a long time since I’ve owned and fiddled with one, and I was always told and I’ve installed. few over the years, when installing an aftermarket cooler you abandon the one in the radiator (clearly this isn’t in the radiator and thanks for the great illustration). Hence the the cooling system regulates the trans temp. NOW, without looking it up I’m certain the OEM thermostat is every bit of 195 to 210 (I’ve seen 220 on some of our fleet vehicles) degrees. And 220 is too hot for any HYD oil. When my new to me van shows up I’ll keep everyone posted on what I find and what direction I went.