I am having to add coolant to my resevoir twice. I can not see a leak anywhere. Haven't saw anything out the tailpipe. Any answer as to where to look. 98800 miles. Just as I am putting it up for sale. Will fix. This is the only problem I ever had.

 

you need to look thoroughly around the truck, i had a small leak on a lower rad hose but it was just the clamp that wasnt sealing properly