The key to proper timing belt function is keeping the belt taut and tight. A broken or malfunctioning tensioner makes this next to impossible. So it's absolutely important that you get a new the moment you start to find yours wearing down.
Replace one or replace all
It's very rare that the tensioner by itself will break down. More likely, a busted tensioner will be the cause of a long cascade of trouble within the same area. That means, odds are good that you will wind up replacing all of them anyway.
Because the tensioner and its associated parts will have this tendency to break down in a cluster, it's a smart investment to replace the tensioner and the timing belt at the same time. Trust us. It will save you the hassle of having to go out an order parts again!
Fit, fit, fit
We say this again and again in many different articles, but the primary consideration is always going to be the specificity of fit for your exact year, make, and model. True, some models and makes will have some similarity in lay out, but the simple fact is that vehicles are too diverse in form for any universality to emerge.
The trick here is to have a point of reference. Automobile owners have two: the first is the busted tensioner; the second is the owner's repair manual. If you intended to shop online and have no numbers for the dimensions, take the time to measure out the diameter, thickness, and take note of the particular appearance relative to the belt.
It still bears mentioning that, even with standardization in the manufacture of tensioners, you still have to be careful not to pick out a tensioner that is made from shoddy materials. Of course, you've no time to fully analyze a product you are trying to buy-especially if it's online. The next best thing is to go with the price. A decent, yet affordable one will rarely be priced lower than $35, and a higher-quality one will rarely tip the scales over $70.