I'm wondering. I only put about 4000 miles a year on my '02 f250 with the 5.4 and manual trans. Owners manual says change the anti freeze every 3 years. Considering the amount driven is this "over kill". How often would you change it. Has the coolant had it because of the time in service? ( I have it done at the dealer with Ford coolant.)

 

whether its used or not coolant has a shelf life. So ten year old coolant still in the original bottle is more or less worthless in comparison to new coolant. You can test your coolant, but honestly the best/easiest method is simply a visual test.. if it looks clean and fresh you are probably good. If it looks nasty or discolored replace it. If it was a diesel on the other hand I would say replace it immediately without even looking at it and do it before the recommended interval... lol