I originall installed mine with a billit Russell thermostat. During the summer it wasn't an issue.
Oil would warm up yo proper operating temp. It took a little bit longer than normal, but not much.
On a cold morning, it's a differant story. The engine warmed up t the
oil didn't. That small amount that flowed through the cooler kept the
oil pretty cold. I tried to cover he coller with duct tape, cardboard, and cardboard held on with duct tape. It was better, but still couldn't get the oil up to temp.
So I now use a completly seperate cooling circuit, with it's own electric pump. It adds a little weight, but works better.