I am wondering if using a thick oil like 10w-40 would do the opposite of protected an old motor, as it would not be able to get into some of the small creeves that smaller weight oil could. I currently run 10w-40 and my engine has 100k so the bearing spaces are prolly a big bigger. But is 10w-40 too much? I am planning on switching down to 10w-30 for the winter.

 

10W-40 is not all that thick and should not be a problem, especially if you live in a southern state.