How Tight Should a Serpentine Belt Be? [Answered]

What is a Serpentine Belt?

A serpentine belt is a long, robust rubber belt that transports power to the engine accessories. Major parts of the engine like the alternator, power steering, air conditioning compressor, air pump, and water pump. The function of all these items relies heavily on a working serpentine belt. In other words, the belt plays a key role in properly operating your car, truck, or SUV.

A serpentine belt is sometimes referred to as a fan or accessory belt. Why? In the beginning, vehicles used to have multiple drive belts that connected the engine to the radiator fan. But today, most vehicles only have one belt with multiple pulleys that power all the accessories. 

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How Long Does A Serpentine Belt Last?

Serpentine belts are expected to last between 60,000 and 100,000 miles. While some belts can last longer, we recommend checking your owner’s manual to learn your vehicle’s suggested belt replacement time frame. The safest route is to replace the serpentine belt during your car’s scheduled maintenance (even if it looks okay). This ensures your belt is actively working and will help you avoid breaking it while driving. Ideally, the belt would last to that 60,000-mile mark, but it’s better to be safe and avoid serious engine damage.

If you’re not sure when your serpentine belt was last replaced (perhaps you’ve purchased a used car), we recommend visiting a certified technician or dealership for a routine vehicle inspection.  

But let’s get to the reason you’re here.

Signs of a Damaged Serpentine Belt

The proper functioning of the serpentine belt lies in its tension. It cannot be too loose or too tight as both extremes can cause the immediate breakdown of the vehicle. How do you know if the tension is incorrect? Here are a few signs that your serpentine belt might be damaged, in need of replacement, or readjusted: 

  • Obvious signs of cracking, fraying, or wear on the belt.
  • You hear squealing or a chirping sound coming from the engine. A loose serpentine belt will often produce a squealing noise.
  • Performance loss in your power steering, car battery draining, or engine keeps stalling.
  • The check engine light or warning light is on your dashboard. Most vehicles today are equipped with an ignition or voltage warning light.
  • Check your engine’s temperature gauge. When the serpentine belt is too loose, it’s not giving the correct amount of power to the water pump—causing the engine to overheat.
  • You hear other unusual noises.

Incorrect tension in the belt will likely produce a squeaky noise. If this happens, you should immediately check the position of the belt. Don’t delay! If the corrective measures are not taken, the serpentine belt will slip over the pulleys and dislodge, resulting in the immediate breakdown of the vehicle.

Step 1: Getting Started 

Make sure your vehicle is parked (ideally on a flat surface). Be sure to wait until the engine is completely cooled off before opening the hood and start work.

Step 2: Locate the Adjustable Tensioner 

Contemporary Process

Most modern vehicles come with automatic belt tensioners with a pulley arrangement. This system has become the standard for automobiles today and has made adjusting the serpentine belt tension easier and more accessible. Inspect the serpentine belt and find the area that needs tension. Locate the adjustable belt tensioner. 

Conventional Process

However, if your car does not have one, the engine accessory that the belt operates has to be loosened from the engine. Most serpentine belt tensioners are below the alternator, attached to the power steering pump, or right below the a/c compressor. You will see the tensioner as it will be a bracket with an adjustable bolt sticking out of the bracket. 

For additional information, look at your manufacturer manual to guide you through the specific parts of your engine. 

Step 3: Loosen the Front Locking Bolt and Mounting Bolt

The front locking bolt is the item that secures the adjustment bracket to the engine accessory. It is secured with a ratchet and a socket. The next step is to loosen the front locking bolt and then loosen the mounting bolt with the ratchet and socket.

Step 4: Tighten the Serpentine Belt

Having located the adjustment bolt at the end of the adjustment bracket, turn the bolt clockwise to tighten the belt. After you’ve tightened the belt, retighten the lock bolt on the front of the bracket using the ratchet and socket.

Step 5: Check the Tension of the Serpentine Belt

To have the proper tension (not too tight or loose), the serpentine belt should have no more than ½ inch of slack. In order to make sure the belt has no more than a ½ inch of slack, you can adjust the belt from the adjustment bolt. If the engine accessory that the belt operates has no adjustment bracket, you must loosen the mounting bolts. You can tighten or loosen the mounting bolt to the accessory with the socket and ratchet. 

How To Tighten A Serpentine Belt

Step 6: Pry Against The Accessory 

Using the ratchet and socket, loosen the mounting bolts to the engine accessory. Using a pry bar, slide the bar in between the accessory and the engine. Pry against it until the serpentine belt is good and tight. Once the belt is tightened, using one hand, hold the pry bar and then, with the other hand, tighten one of the accessory mounting bolts.

Step 7: Check the Belt Tension 

Re-check the tension of the serpentine belt. Again, the belt should not have more than ½ inch of slack. If the belt needs adjusting, use the pry bar until there is no more than ½ inch of slack, as discussed before. Once the tension is correct, tighten all the remaining accessory bolts using the ratchet and socket.

Start the engine and let it run for a bit. Listen for any squealing sounds. Please turn it off and re-check the belt’s tension to ensure it’s still correct. Repeat the steps if the belt is still not tightened correctly.

Conclusion 

Given all the above details, it would be wise to pay attention to the general condition of the serpentine belt within the time period recommended in the manufacturer’s manual. While the belt is made to last a long time, be sure to make checking the belt a part of your auto inspection routine. 

The life and quality of a well-maintained and functioning belt are much better in the long run for both your car and your wallet. Keep the maintenance of your vehicle’s serpentine belt in check, and enjoy your time on the road without worrying.

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