Steve,
I hope your suggestion for the -8 lines was tongue-in-cheek... It won't reduce the temperature, just the flow to the bearings.
The "best"
oil temp is in the 200-230F range. That's hot enough to boil off water and gasoline fractions that contaminate the
oil. There are a couple of ways to accomplish this with the cooler still in the system.
Thermostat - some adapters have a small thermostat/pressure relief built in. Alternately, there are thermostats that are installed in-line with both hoses, bypassing the cooler when it isn't necessary.
Block off the air through the cooler. You don't necessarily have to put anything in front of the cooler - something to prevent air from flowing
through the cooler will be almost as effective.