Toyota Echo drive belt

Car has thrown belt twice in the past year, leaving me stranded. Mechanics checked all pulleys, etc and can find no reason. This has been 2 different mechanics. It’s a great car otherwise. Any ideas?

There really aren’t too many possibilities here.
The problem has to be one of the following, IMHO:

A worn-out belt tensioner
Pulleys that are bent or out of proper alignment
The wrong belt

The only additional possibility causes me to ask if the belts have been thrown while driving in wet weather. If the answer is yes, then you should also check for a missing splash shield underneath the engine compartment. If a splash shield is missing, the spray of water onto the belt and pulley could definitely cause problems–especially if the tensioner is weak.

It was dry both times. Belt didn’t break so much as shred. Mechanic said he checked all pulleys for alignment and spin while the belt was off and found no problems. I just find it hard to believe it’s a coincidence.

Actually, there is one additional possibility.
If the bearings in an idler pulley or the tensioner are going dry, this would cause that part to bind up, thus causing the belt to be dragged across the sticky tensioner or idler pulley. This dragging could shred the belt.

Given that the Echo has not been made for…several years…these bearings are about the right age to be possibly going dry. Try taking the belt off, and spinning all of the pulleys that carry the belt normally. If you hear any squeeking noises (especially in the AM, when temps are lower), or if you feel that there is any binding, you have found your culprit.