Be aware of how the thermostat operates. When cold, the valve is mostly closed and about 10% of the
oil passes through the cooler. The other 90% is routed back to the block. When hot, the valve is mostly open and about 90% is routed through the cooler. The other 10% is shunted directly back to the block.
It's done that way so all of the
oil warms up at the same rate. You wouldn't want the valve to open, and suddenly get a slug of cold
oil into the system.
The down side of this is that when it's cool out (or cold), the oil still won't warm up. I used to keep mine covered with duct tape during the winter. That helped, but some days it just would not warm up.