I love maintaining my 2007 Toyota Yaris. It isn’t a perfect car, but it is incredibly reliable and easy to work on.
One issue I’ve had is that the serpentine belt loves to squeal. It is such a common issue on this model that Toyota actually increased the recommended belt tension after the car came out. So to fix the squeal, you just have to tighten the belt more.
But how much more? Too loose and it will still squeal (and ruin the belt). Too tight and you can damage more expensive components in the car.
The solution is an inexpensive Gates 91132 belt tension tester. I paid about $11 on Amazon. The price fluctuates a bit so you may have to pay a few dollars more if you want it now.
This little gizmo is very easy to use. You simply align it in the center of the belt and push. When you hear it click, you stop pushing and check the value.
To check the belt tension on a 2007 Toyota Yaris, you have to crawl under the car and push up on the middle of the belt between the crank and the air conditioner. The proper tension is 102-103 Ft. Lbs.
It also helps to have a belt tensioner. I added one to my car a few years ago, and it has saved me so much time when changing the belt.