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How To Inspect & Replace a Serpentine Belt
How to Check It and Replace It

by Larry Carley copyright

Most late model front-wheel drive cars and minivans as well as rear-wheel drive cars and trucks have a serpentine belt to drive the engine's accessories. Serpentine belts have replaced multiple V-belts because a single belt is more compact, cheaper and simpler to install than multiple belts. By snaking around the various pulleys, both sides of a serpentine belt can grip and turn the pulleys on the alternator, water pump, A/C compressor and power steering pump.


Serpentine belts are easy to identify because they are flat on the outside and ribbed or grooved on the underside. Most are also much longer than a typical V-belt. Serpentine belts are also wider and flatter than V-belts. A typical V-belt will usually measure about half an inch wide and a half inch thick. A typical serpentine belt, by comparison, will measure about an inch wide but only about one eighth of an inch thick. The flatter cross-section gives the belt greater flexibility, reduces internal friction and heat buildup. Heat is a belt's worst enemy, so anything that allows a belt to run cooler will help it last longer.


As a rule, serpentine belts in older vehicles typically had a recommended replacement interval of 50,000 to 60,000 miles . But on most newer vehicles (10 years or less in age), the recommended replacement interval is usually 100,000 miles. Serpentine belts in late model vehicles are made of EDPM (ethylyne propelen dyeen monomer) which is a very durable synthetic rubber. EDPM belts will often last well beyond 100,000 miles. Even so, it is a good idea to replace the belt at the recommended interval to reduce the risk of a belt failure and breakdown.


Sometimes a serpentine belt will start to squeal, glaze or crack at lower mileages. The high-pitched squealing noise is caused by a glaze that develops on the outer surface of the belt, which may be due to pulley misalignment and/or slippage (loss of belt tension or a weak automatic tensioner). The noise does not affect belt operation or reliability (unless it is slipping), but the noise can be very annoying.

Belt replacement is often the only way to get rid of the noise. You can spray a noisy belt with aerosol belt dressing lubricant. These products will often quiet belt noise for awhile, but sooner or later the noise will come back.

If a new belt is still noisy, the noise may be due to a weak automatic tensioner that is allowing the belt to slip, or misalignment or wear in the pulleys.

Dayco, a supplier of original equipment and aftermarket belts, makes a special "W" profile replacement serpentine belt for high mileage vehicles (80,000 or more miles) that may have slightly worn or misaligned pulleys. The unique shape of the grooves on the underside of the belt combined with special fibers and materials in the belt itself help it run quieter than a standard replacement belt. To watch Dayco's informational video on their "W" profile serpentine belts, Click Here.

serpentine belt
A visual inspection will reveal any obvious flaws.
If you see cracks or pieces of rubber missing, replace the belt.
The belt should also be replaced if it is contaminated with grease or oil.


You should inspect your serpentine belt periodically, say every time you change the oil or add windshield washer fluid to the reservoir.

If the belt is badly cracked, frayed or has chunks of rubber missing from its ribs, the belt should be replaced immediately.

Minor cracking on the ribbed side of the belt is okay, but heavy cracking would tell you the rubber is getting hard and the belt is near the end of its service life. But this only applies to older serpentine belts made of neoprene synthetic rubber.

A good rule of thumb for older chloroprene-based serpentine belts (neoprene belts) is that if cracks are observed 3 mm (1/8 inch) apart all around the belt, the belt is reaching the end of its service life and should be changed. Small cracks spaced at greater intervals are normal on older belts as they age, and do not mean the belt needs to be changed.

serpentine belt cracks
Cracks in the rubber mean the belt could fail.
Better to replace it now than risk a belt failure and breakdown.

With late model serpentine belts of EDPM, you probably won't see any cracks because EDPM seldom cracks as it ages. This makes it more difficult to determine the condition of the belt. A high mileage belt may still look like new, but the V-grooves on the underside may be badly worn allowing the belt to slip. Slippage can lead to noise, pulley wear, engine overheating, battery undercharging, and even false engine codes (A/C compressor slippage codes, power steering codes, knock sensor codes, etc.).

A classic symptom of a worn serpentine belt is belt noise when you rev the engine. If the ribs on the underside of the belt are worn, the belt can lose its grip and slip under load. A weak automatic belt tensioner or insufficient tension with a manually adjusted belt can also allow the belt to slip. If you see any belt flutter when you rev the engine, it probably does not have enough tension.


Belt wear is difficult to see by just looking at the belt, so several belt manufacturers have developed simple tools for checking the depth of the grooves in the underside of the belt. You can get a free tool at

The tip of the tool is placed flat into the grooves on the underside of the belt. If the gauge part of the tool is ABOVE the surface of the belt, the belt is not worn. But if the gauge is FLUSH or BELOW the ribs on the belt, the belt is worn out and needs to be replaced.


Place gauge on belt....Then check height of gauge.

Instructions for the belt gauge. Click on the image to enlarge.

Any serpentine belt that shows chunking or is obviously damaged needs to be replaced immediately as it will soon fail.

Also check the belt to see if it is contaminated with oil or grease. Petroleum products can weaken rubber over time and shorten the life of the belt. Oil and grease may also cause the belt to slip, which may cause the alternator to undercharge, or the water pump to not circulate enough coolant to keep the engine from running hot or overheating.


If your serpentine belt breaks or comes off its pulleys, it is bad news. The belt is the all-important link between the pulley on the end of the crankshaft and the pulleys that drive most or all of your engine's accessories. So a belt failure usually means loss of engine cooling, loss of battery charging, loss of power steering assist, and loss of air conditioning. In short, a belt failure means a breakdown.

It's hard to predict when exactly a belt will fail because appearances alone don't revel what's going on inside a belt. Some high mileage belts that still look good as new on the outside may be dangerously weak on the inside and on the verge of failure.

To reduce your risk of a breakdown, therefore, you should replace your serpentine belt at 50,000 to 60,000 miles for preventative maintenance.

If your old belt is glazed or is squealing, be sure to check the automatic belt tensioner. It may be weak or stuck. You should also check the alignment of the pulleys with a straight edge. More than about a quarter inch of misalignment can be enough to cause a problem (an eighth of an inch if pulleys are spaced close together!).


If the old belt is still intact and has not broken or come off its pulleys, note how it is routed BEFORE you remove it. If you cannot find a belt routing decal in the engine compartment or under the hood, draw a picture of how the belt is routed. Or, take a digital photo for reference in case you forget.

You can also find belt routing diagrams (for a fee) on Vehicle Manufacturer Service Information Websites or at

NOTE: A serpentine belt will usually go on only one way. If the belt does not seem to fit (not long enough or too long), and the replacement belt is the same length as the original, the belt is probably misrouted. Recheck the routing diagram and try again.

In some instances it may be possible to install a serpentine belt the wrong way. If this happens, one or more pulleys will rotate in the WRONG direction, affecting the operation of the alternator, water pump, A/C compressor or power steering pump. This can cause major problems.

Replacing a serpentine belt can be tricky on many front-wheel drive cars and minivans with sideways (transverse) mounted engines because belt accessibility is limited. There may be little room between the pulleys on a transverse-mounted engine and the left fenderwell. On some applications, you may have to disconnect and remove an engine mount to replace the belt!

To release the automatic belt tensioner, you may need a special tool designed for this purpose.

If the engine does not have an automatic belt tensioner, but uses a manual adjuster or bolt, a belt gauge should be used to adjust belt tension to specifications. A belt that is too loose may slip or come off its pulleys, while a belt that is too tight may overload accessory drive bearings or the belt itself, causing premature belt or component failure.

If you are trying to fit a serpentine belt to a custom application or an engine that did not originally have A/C but has an A/C compressor or other belt-driven accessory now, the fitment guide on this website can help: Dayco Fitment Guide. Click on the Serpentine Belt tab, then enter the belt length and number of ribs to find out what belt fits the application.

StretchFit serpentine belt


To save money, auto makers have eliminated the automatic tensioner for the serpentine belt on some late model vehicles. Older applications include 2004 and up Mazda MPV & Tribute, 2005 & up Ford Escape and Taurus, 2007 & up Chrysler Sebring, Dodge Stratus and Dodge Nitro, some 2008 and up GMC and Chevy trucks, and 2008 and up Hummer H3.

On these vehicles, the serpentine belt has to be stretched over the last pulley when it is replaced. The trick is to route the belt as far as you can, then start it partially over the last pulley. You then rotate the engine by hand to finish pulling the belt over the pulley into place.

Gates has a special tool for this purpose that makes the installation much easier. For more information about StretchFit serpentine belts and their replacement, Click Here to view Gates instruction sheet.

One important point to note about StretchFit belts is that they cannot be reused if they are removed. They are designed to stretch ONCE and that's it. If you try to reuse one of these belts, it won't maintain tension and will likely slip or come off its pulleys.

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