How To Diagnose A Failing Tensioner

When your belt tensioner fails, it can no longer keep the serpentine belt tight. This either reduces or removes the belt's ability to power some accessories. Do you want your Mazda to be in tip top shape? Inspect your belt tensioner as soon as you notice the symptoms of failure and replace it if needed.

If you're not sure how to do this, we got you covered with this tutorial.

Telltale Signs Of A Failing Belt Tensioner

Belt tensioner

If the belt tensioner on your Mazda fails, you'll notice these symptoms while driving:

  • Squealing, ratting, fluttering, or squeaking noise coming from the engine compartment when idling or at low RPMs
    • This means that the belt tensioner isn't keeping the serpentine belt tight enough
  • Battery warning light coming on
    • This means that the alternator has become too weak to power the battery
  • Low power from the power steering system
    • When the tensioner fails to keep the belt tight, it can't power the power steering system as well anymore
  • Dim headlights
    • This happens when the belt isn't tight enough to power the vehicle's electrical system
  • Overheating engine
    • When the tensioner can no longer keep the belt tight, the water pump fails to keep the engine cool
  • Prematurely worn serpentine belt
    • The belt can develop cracks from excess heat, and fraying from slipping side to side

If two or more of those symptoms crop up, something is probably wrong with the belt tensioner or the serpentine belt. The symptoms of a failing serpentine belt are like the symptoms of a failing belt tensioner.It's because a failing belt tensioner can't keep the belt tight enough to power all the accessories. In other words, the belt itself may be in good shape, but it's performing as if it has failed due to a bad tensioner.

Before ordering a replacement tensioner, you want to make sure that it's the issue rather than the belt or other pulleys.

Inspecting The Belt Tensioner On Your Mazda Engine

There are several different ways a belt tensioner can fail:

  • The tensioner spring gets too weak. When this happens, it can't keep the belt tight anymore. This leads to belt performance issues, and possibly damage on the belt.
  • The tensioner pulley bearing fails. When this happens, it either gets stuck or starts wobbling. In either scenario, the belt fails to power accessories and gets damaged.
  • Rust builds up around the tensioner spring and/or pulley bearing. This causes the tensioner to get stuck.
  • The belt wears into the pulley. This results in physical damage on the pulley, which compromises its ability to support the belt.

The best way to confirm that you've got a bad belt tensioner is to pop the hood and give it a visual inspection. Make sure the engine is off and cool first!

What To Look For

The first thing you want to do is find the belt tensioner. First, find the serpentine belt path. The tensioner is on that path. In some vehicles, there are some parts in the way that you would need to remove first. Luckily, you don't encounter this issue much with Mazda engines. Often times, when you open the hood of a Mazda vehicle, you'll see the serpentine belt path right in front of you. Find the tensioner, and then inspect it.

Note that we based this tutorial on a Mazda spring-loaded tensioner. Diagnosing a hydraulic or manual adjustable tensioner requires slightly different steps. Yet, it can't hurt to follow this tutorial for the basics.

  1. First, tug on the serpentine belt. Is it too tight or too loose? Or does it feel just right? Next, tug it again but do it next to the tensioner pulley. Watch the way the tensioner pulley reacts.
    1. If the tensioner pulley doesn't move when you tug it, it's frozen in place. In that case, you need to replace it.
    2. If the tensioner pulley moves, but doesn't extend quickly to the point where it puts the right amount of tension on the belt, the spring may be bad.
  2. Spin the tensioner pulley. Remove the serpentine belt from the tensioner pulley. With your hand or a torque, spin the pulley in the same direction it spins in when the engine is on. If it's not spinning smoothly, the tensioner is somewhat stuck.
  3. Visually inspect the tensioner. Grab a flashlight and examine the tensioner. Look for clear signs of damage like rust, corrosion, or cracks.

Other Parts To Check

The belt tensioner may be fine, but there's another issue that's preventing the accessories from being powered. So if the belt tensioner seems OK, check the following parts:

  • Serpentine belt
    • Look for fraying, cracks, or other signs of extreme wear
  • Other pulley bearings
    • Look for looseness, rotation issues, or physical damage

Finding A Replacement Tensioner

OEM mazda belt tensioner

If you find that your tensioner is bad, the next step is to find a replacement unit. The good news is it's easy to find a genuine OEM replacement tensioner at wholesale pricing. All you need to do is look up your Mazda model here to find the right part number.

You may want to replace the serpentine belt too, if it's old or worn enough. In that case, we carry OEM serpentine belts at wholesale pricing too!