I used to use cardboard to cover the
oil cooler and part of the radiator, to get my coolant and
oil temps up during my winter drives to and from work.
I now use the Beaumont adjustable
oil cooler bypass valve (along with upgrading my lines AND oil cooler to AN12) and the temps come up quite nicely, along with a "cleaner" look in the winter (relatively speaking).
Here is my setup.
Jim Kellogg