I use a manually operated by-pass valve. It is integrated into the remote filter mount.
It allows me to proportionally flow as much
oil as I want through the cooler. It has -12AN ports for low flow restrictions.
I run -12AN from the engine to the valve/filter. Then -10AN to my
oil cooler.
I think my
oil temp runs on the cold side most of the time, even wit the oil cooler closed. But when I drive with higher engine revs, say maintained at 3500 and up, the oil temp gets dangerously hot and I need the cooler. At a track event for example.
More info on these valves are at:
www.beaumontmetalworks.com