Congratulations, sounds like you have a good example. Thirty one miles per gallon is a little above the reported average but good. The majority report less but a few do report 31-32 mpg. Yes pump uses the engine base oil to lubricate it's bottom end. You are lucky as the fan control circuit and motor are quite straightforward compared to the five cylinder cars. . Usually the brushes need changed in the fan motor seems to be the common ailment but check for fuse etc first. Drive the car in a reasonable fashion and change the oil on schedule and it could serve you for a very, very long time. As for draining the oil cooler I do not know. You might want to look in the archives for that. Especially look in the archives regarding your cruise control.