[me and my metro]

Those are designed to slightly cool hot oil down to coolant temp. They are set up the same way on the Ford gas engines I work on. The GM coolers that use 1/2” tubing to connect to the radiator are only partial flow so even if they plug up the engine will still live. I know you are looking to warm the oil quicker for fuel economy. Thinner oil may give better results in my opinion. The problems I have seen here is cold oil in fire fighting equipment and engine failure. We have installed oil sump heaters in some of the gas engine trucks with good success. I had one on a VW bus back in the early 80s to aid cold starts and faster warmups on an air cooled engine.