Just did the first oil change on my 77 300d. I am curious, does the oil cooler drain when the oil is changed? I had read somewhere that there was a thermostat in the oil cooler lines. Wouldn't this stop that oil from draining? If so, wouldn't it be advantageous to make sure that the oil did drain out of the cooler? If it doesn't drain normally, does anyone know what to do to cause it to drain?