After r&r of my water pump, I was confused about the strange path the outer belt takes. It barely contacts the fan/water pump pulley. (The inner belt only wraps that pulley about 90 degrees)There are two idler pulleys, the upper being adjustable. The lower seems completely unnecessary. It does not alter the path of the belt only slightly. If it were eliminated a slightly shorter belt may be in order, but the upper adjustable idler may well take care of that.

Now, I have air conditioning, but it occured to me that on a vehicle without air, there would not be a way to adjust the belt tension unless the lower idler were adjustable. Am I missing something here? The vehicle is a 1977 F250 460 auto.