The serpentine belt that drives the accessories on late model engines has an automatic tensioner that keeps the belt tight. The majority of people know the belts certainly are a maintenance item and at some point must be replaced. But many tend not to know the spring-loaded automatic tensioner that keeps a serpentine belt tight can also put on out or grow to be weak. This can trigger a variety of difficulties in case the tensioner isn’t replaced whenever a new belt is put in.

The automatic tensioner includes a coil spring inside that applies just the appropriate quantity of force against the belt to keep it tight. The tensioner also delivers just a little “give” so it may possibly absorb and cushion shock loads within the belt that occur if the A/C compressor clutch cycles on and off. What is far more, the tensioner automatically compensates for put on and keeps the belt underneath continuous tension.
serpentine belt tensioner exploded view

But practically nothing lasts forever, not belts and never automatic tensioners. The typical service life of a serpentine belt is about 60,000 miles or five many years. Once the belt nears the finish of its lifestyle, it might turn into cracked, glazed and noisy. Cracks about the underside of a serpentine belt are typical. However, should you see additional than three cracks within a three inch section on any one rib, the belt has already utilized up 80% of its intended life. Replace it now.

If an aging belt will not be replaced, it may break triggering a loss of drive torque to all of the engine’s accessories. When the water pump stops turning, the flow of coolant stops and the engine starts to overheat. Once the alternator stops turning, there’s no charging output as well as the battery begins to run down. When the power steering pump stops turning, the steering suddenly gets incredibly stiff and tough to steer.

All too normally, an outdated serpentine belt (or a broken belt) will be replaced by using a new one. But the automatic tensioner will not be inspected for making confident it really is even now working effectively and it is in superior affliction. This error can lead to rapid belt slippage, wear and repeat belt failures should the tensioner is weak or worn out.

Belt tension is important. As well very little tension may permit the belt to slip and squeal. Slippage also causes the belt to run hot and age prematurely. And should the belt is truly loose, it may come off its pulleys. A lot of tension on a belt may well overload the belt as well as the shaft bearings to the water pump, alternator, power steering pump and air conditioning compressor, probably primary to premature failures in these parts, too.

Belt tensioners had been very first made use of back while in the late 1970s. These early units have been fixed tensioners that essential manual adjustment. Then automatic belt tensioners arrived during the mid-1980s. The spring-loaded design eradicated the require for manual adjustments and assured suitable belt tension for the daily life of the belt. Because of this, the tensioner is often ignored when a belt is replaced. Even so, the tensioner must constantly be inspected when changing a belt for the following causes:

* Rust or corrosion can jam the tensioner housing and prevent it from rotating freely. A frozen tensioner cannot preserve proper belt stress. Corrosion is normally a end result of road splash, specially in locations wherever roads are heavily salted through the winter.

* Dirt or mud could also jam the tensioner housing.

* A loose or worn pivot arm can allow unwanted movement that leads to belt noise and misalignment. As time passes, this will increase belt wear and cause premature belt failure.

* A worn bushing inside the tensioner pulley could cause vibrations and noise. Should the bushing seizes, it might trigger the belt to snap.

* A weak or broken spring within the tensioner can not sustain correct tension and also the belt will slip. Springs shed tension as time passes from exposure to warmth.

* Cracks or harm to your tensioner housing or pulley arm may possibly reduce it from rotating smoothly and sustaining good belt stress.

Signs and symptoms Of the Poor BELT TENSIONER

Signs that ordinarily indicate an automatic tensioner has reached the end with the road involve:

* Belt slipping (on account of reduction of tension). View the tensioner arm motion whilst the engine is idling. There really should be a gentle arm motion as accessories turn on and off (such because the A/C compressor clutch engaging and disengaging). If the tensioner pulley does not move at all, the tensioner might be caught. You’ll be able to check for this later on using the engine off. Also watch for extreme chattering or tensioner arm oscillation although the engine is idling. This can be attributable to a worn damper in the tensioner. Excessive arm oscillation must be viewed being a warning sign that the damper has probably failed or is failing as well as the tensioner needs to be replaced now. If it’s not replaced, it may possess a hammering effect on nearby accessories resulting in the shaft bearings around the accessory to fail.

* Battery runs down (since belt is slipping and never turning the alternator quickly sufficient)

* Belt glazing (due to slipping). Any glazing (shine) around the underside of your belt signifies that the belt continues to be slipping. Slippage is usually brought on by not ample spring tension about the tensioner, a failing element bearing, contaminated pulleys or an elongated belt.

* Excessive motion or rocking in the tensioner pulley, or “belt flutter” if the engine is operating. What this means is the spring in the tensioner is weak and/or the bushing is worn. The tensioner needs to be replaced.

* Wobble in the tensioner pulley (or idler pulley). Wobble usually means the bearings are shot.

* Belt or tensioner noise. The tensioner should really be quiet when the engine is operating. Any squealing, rumbling, growling or chirping noises must be investigated to determine the trigger. A mechanic’s stethoscope may be used to pinpoint the supply of the noise. The probe must be placed against the bolt within the center on the tensioner pulley wheel to listen for bearing noise. The idler pulley(s) must also be checked as the bearings within this component can wear out, also. The same goes for every one of the engine-driven accessories (water pump, alternator, PS pump and A/C compressor).

* Pulley damage. Physical harm of any kind to the automatic tensioner pulley may possibly indicate extreme stress or physical interference. Should the pulley is broken, replace the tensioner assembly not just the pulley. If an idler pulley is damaged, examine the tensioner also since vibrations due to a bad idler pulley may perhaps damage the tensioner.


Check out the movement from the tensioner arm together with the engine off. Use a socket with a long take care of ratchet or breaker bar on the tensioner pulley center bolt to rotate the tensioner. There aren’t any specs for measuring the quantity of resistance featured from the tensioner spring, but when the tensioner features tiny resistance it might indicate a weak or broken spring. If it fails to move in any respect, the tensioner is jammed and has to be replaced.

View for looseness from the arm once the tensioner is rotated. The arm should really not wobble or twist. If it does, the tensioner bearings are worn as well as unit must be replaced.

Also note the position of your arm within the automatic tensioner. Numerous units have marks on the housing that display the standard variety the arm can pivot. When the place with the arm is outside these marks, it indicates a problem (the belt may well be as well extended or as well quick, or even the tensioner may possibly be jammed).

Note the put on pattern about the tensioner and idler pulley(s). Misalignment and bearing wear can cause the belt to track off-center. This will likely bring about the belt to wear rapidly. The tensioner and idler pulley bearings could be checked by removing the belt and spinning the pulleys by hand. All pulleys really should turn freely without any binding, roughness or wobble. Any binding, roughness or wobble implies these parts are terrible and have to be replaced.

Pulley alignment should really also be checked to generate confident there is not a mounting issue while in the belt drive system. Pulley alignment may be checked by putting a straight edge against the pulleys, or using a unique laser alignment tool designed for this function. Any side abrasion on the belt generally signifies there may be misalignment during the system. It will have to be identified and corrected just before setting up a new belt.
belt tensioner


Should the automatic belt tensioner has failed (and the engine includes a wide range of miles on it), it truly is in all probability a fantastic plan to change the idler pulley(s) on the same time. Why? As the shaft bearings on all the pulleys may have the identical amount of put on. If they’re reaching the finish of their services existence, replacing them now will restore the pulleys to like-new situation and decrease the threat of a breakdown on account of a belt or pulley failure.

Aftermarket automatic tensioners tend to be a much better replacement decision than an original equipment tensioner, primarily on older vehicle applications. Some OEM tensioners (Chrysler 3.0L, 3.3L and 3.8L, one example is) weren’t pretty robust and have expert a higher failure rate above the years. As opposed to only copy these OEM tensioner styles with their inherent flaws, some aftermarket companies have re-engineered their parts to overcome the weaknesses with the authentic design and style. Therefore, some aftermarket replacement tensioners may not search specifically the same since the authentic. But there is a cause why: these parts happen to be redesigned to outperform and outlast the unique parts they change.

A particular tool that could be essential when replacing a serpentine belt or automatic tensioner on the transverse-mounted engine in a front-wheel drive car is actually a specific serpentine belt removal tool. The tool has a extended, flat extension handle that allows a socket to be placed within the tensioner bolt so the tensioner in a tight engine compartment is usually conveniently rotated to relive strain on the belt. With out this tool, the task is just about not possible on some autos.

One thing else you may want is a belt routing diagram so the brand new belt may be effectively routed all around every one of the pulleys. Spend attention when you are eliminating the belt, and in the event the underhood decal that shows how the belt is routed is missing draw a picture (or consider a digital photo) which means you know in which the belt goes. Serpentine belts can be really confusing.
StretchFit serpentine belt


To conserve dollars, auto makers have eradicated the automatic tensioner for your serpentine belt on some late model automobiles. Applications contain 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 automobiles, the serpentine belt has to be stretched above the last pulley when it truly is replaced. The trick is to route the belt as far as you could, then start it partially in excess of the last pulley. You then rotate the engine by hand to finish pulling the belt in excess of the pulley into place.

Gates includes a distinctive tool for this function that makes the installation a great deal easier. For extra information about StretchFit serpentine belts and their replacement, Click Here to view Gates instruction sheet.