In a few words:
The timing belt is a rubber strap that keeps the valves and the engine pistons mechanically synchronized, connecting the crankshaft to the camshaft.
If it breaks or fails it can provoque important damages in the valves, pistons and/or in the engine head. This is why we recommend you to make regular inspections to replace it before it starts failing.
As a general rule, the life time of the timing belt oscillates between 37280 mi and 99420 mi or 5 years, whichever comes first. Check the owner's manual of your Econoline to know the exact data of your car.
When changing the belt, replace the tensioners as well. If the belt of your Econoline activates the water pump, it is convenient that you replace it too. We make this recommendation because when you replace the belt, the highest cost is the work that changing it takes, and not the replacement part itself. When you change your belt but leave the water pump and the old tensioners (which are cheap to buy), you are taking the risk of them failing and in that case you will have to repeat the work, making an expense that you could have saved.
The timing belt is usually confused with the auxiliary belt, also called alternator strap, although they have very different functionalities. The latter is the one in charge of moving the mechanical accessories of the car that are located outside of the engine: the alternator, the air conditioner compressor and the power steering pump, amongst others.
Some vehicles use a distribution chain instead of a belt. The advantage of this is its durability, which is usually much longer. The disadvantage of this is that they are usually noisier and more expensive.