Multi viscosity oil was created for one thing. Weather. So it can be one weight in cold weather and another in warm. That's all. It has no better cooling properties than any other oil. Modern oils are very advanced nowadays, including single weights. Single weight oils have been used a very long time with great success. The modern additive packages is in them as well, so they are every bit as good as a multi viscosity oil. These old motors will run with transmission fluid in the crankcase. They don't give a damn as long as they are lubricated.
