5 Symptoms of a Bad Serpentine Belt Tensioner (and Replacement Cost)
When something goes wrong with your car’s serpentine belt tensioner, it can affect multiple systems and leave you wondering what’s happening under the hood. This small yet crucial part keeps your engine’s belt tight and running properly.
If you’ve noticed unusual noises, warning lights, or other strange behaviors from your vehicle, a faulty tensioner might be to blame. Read on to learn how to spot the signs of tensioner failure, what it’ll cost to fix, and whether you can continue driving until your service appointment.
What Is a Serpentine Belt Tensioner?
A serpentine belt tensioner is a component that keeps your vehicle’s serpentine or drive belt at the proper tightness. Maintaining this tension is essential, as it prevents the belt from slipping or making noise. Just as important, the serpentine belt tensioner ensures power transfers correctly from your engine’s crankshaft to other parts that need to run, like your alternator and power steering.
You’ll find your vehicle’s serpentine belt tensioner attached to the front of the engine, directly forward of the timing cover itself. As a general rule, this component sits in direct line with your engine’s crankshaft pulley and all the other belt-driven components (alternator, power steering pump, A/C compressor, etc.).
Serpentine belt tensioners are designed in a number of different configurations, largely depending upon the type of engine in the vehicle. The most common types are manual tensioners, spring tensioners, and hydraulic tensioners.
Manual tensioners require periodic adjustment of tension, while spring tensioners are spring loaded to maintain tension automatically. Hydraulic tensioners use pressurized oil to maintain adjustment and buffer changes in tension.
Related: Serpentine Belt vs Timing Belt (What’s the Difference?)
Signs of Serpentine Belt Tensioner Failure
The failure, or impending failure of a vehicle’s serpentine belt tensioner is often accompanied by one or more secondary symptoms, of varying severity. Quickly recognizing and reacting to these symptoms proves key when attempting to fix the problem and get your vehicle back to normal operation.
#1 – Consistent Squealing From Front of Engine Bay
Without proper tension, it’s normal for a vehicle’s drive belt to slip, producing a high-pitched squealing noise. This noise generally increases in volume under higher RPMs, such as when you accelerate or when the engine is working harder.
This squealing may be particularly loud when you first start your car in the morning or after it’s been sitting for several hours. This happens because the belt and components are cold, making proper grip more difficult.
While a squealing noise often means a tensioner problem, the belt itself could be the culprit even with a good tensioner. An old, glazed, or contaminated serpentine belt (from oil or coolant leaks) can also squeal despite proper tension.
To determine whether the tensioner or the belt is at fault, check the belt’s condition, looking for cracks, glazing, or contamination. If the belt appears in good condition but is still noisy, the tensioner is more likely the problem.
Read Also: 5 Causes of Idler Pulley Noise
#2 – Illuminated Battery Charging Light
As a vehicle’s belt slips from inadequate tension, rotational force is reduced to all other drive pulley-equipped components, including the vehicle’s alternator. As a result, charging issues can result, leading to the illumination of the vehicle’s battery light.
As a vehicle’s belt slips from inadequate tension, rotational force is reduced to all other drive pulley-equipped components, including the vehicle’s alternator. As a result, charging issues can result, leading to the illumination of the vehicle’s battery light on your dashboard.
This warning light is particularly concerning because your alternator is responsible for keeping your battery charged and powering all electrical systems once the engine is running. With insufficient belt tension, your alternator might not spin fast enough to generate adequate power.
You might notice this symptom particularly at idle or when using multiple electrical accessories simultaneously (headlights, wipers, heated seats, etc.). If you simply ignore it, the problem can progress to the point where your battery drains completely, causing your vehicle to stall unexpectedly or fail to restart after being parked.
#3 – Improperly Tracking Belt
In severe cases of imminent belt tensioner failure, it is not uncommon for a belt to begin tracking across all pulley faces at an irregular angle. This can even become bad enough that an engine’s belt is routed completely off one or more pulley faces, which can cause immediate loss of functions like power steering.
You can check for this symptom by visually inspecting your serpentine belt with the engine off. A properly functioning belt should run centered on each pulley, following a smooth path throughout the system. If you notice the belt riding toward the edge of any pulley, or see marks on the sides of the pulleys where the belt has been rubbing, your tensioner is likely failing to maintain proper alignment.
This misalignment creates excessive wear not just on the belt, but potentially on pulley bearings as well. If the belt comes off completely while driving, you’ll immediately lose power steering, alternator function, and potentially coolant pumping ability, which could lead to overheating and significant engine damage.
#4 – Abnormal Belt Wear
In the event of a failing belt tensioner, you might also notice that the engine’s drive belt begins wearing irregularly. If the same pattern of wear becomes quickly evident on a second drive belt, after initial replacement, further inspection of the vehicle’s belt tensioner will be necessary.
Normal belt wear appears as even, small cracks perpendicular to the belt length after many miles of service. Abnormal wear from tensioner problems might include glazing (a shiny, hardened surface), fraying edges, missing chunks of the ribbed surface, or excessive cracking that develops quickly.
These unusual wear patterns occur because the belt is either too loose (causing slippage) or too tight (causing excess friction and heat).
A good inspection practice is to twist the belt slightly to see the ribbed side and look for these wear indicators. If you’ve recently replaced your belt only to find similar issues developing again within a few thousand miles, the problem almost certainly lies with your tensioner rather than the belt itself.
#5 – Visually Suspect Tensioner Irregularities
If upon inspecting your vehicle’s drive belt and tensioner, you note points of concern related to the way your engine’s belt tensioner appears, there is valid cause for your concern. Spring tensioners often begin exhibiting noticeable rust stains or cracks extending from their bearing holes when failing, while hydraulic tensioners typically begin losing fluid to a noticeable degree.
You can perform a basic visual inspection by looking at the tensioner assembly with the engine off. Look for any fluid leakage around a hydraulic tensioner, which indicates seal failure. For spring-type tensioners, check for rust, which suggests moisture has compromised the internal components.
Another good test is to observe the tensioner pulley’s movement with the engine running (from a safe distance, without any loose clothing or items that could get caught). A properly functioning tensioner should maintain steady pressure against the belt with minimal wobble or vibration.
Excessive movement, a visibly bent tensioner arm, or unusual noises directly from the tensioner itself (grinding, clicking, or rattling) are all serious indicators that replacement is needed soon.
Serpentine Belt Tensioner Replacement Cost
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The cost associated with replacing a vehicle’s serpentine belt tensioner typically varies, depending on the make, model, and year of your vehicle. Nonetheless, such repair work tends to be relatively affordable in most cases, and can often be tackled as a DIY project if you have some mechanical know-how.
Generally speaking, you can expect to pay $150-$300 to have your vehicle’s serpentine belt tensioner replaced. Of this cost, approximately half can be attributed to labor costs, while the other half accounts for the purchase of a replacement tensioner. In most cases, you can find a replacement serpentine belt tensioner at virtually any chain auto parts store, with reasonable availability.
As mentioned above, if you’re looking to cut expenses where possible, you might consider replacing your vehicle’s serpentine belt tensioner yourself. Doing so can easily reduce the overall cost of replacement by approximately 50 percent, bringing the total expected cost of this project down to $75-$150.
If your vehicle has a spring-loaded belt tensioner, a serpentine belt tool set make removal and installation much easier.
See Also: Timing Belt Tensioner Replacement Cost
Is It Safe to Continue Driving?
Attempting to continue driving with a faulty serpentine belt tensioner is not advised, especially for lengthy periods of time. This component is designed to maintain optimal tension on your vehicle’s drive belt or serpentine belt, preventing it from slipping or becoming dislodged. Once a belt tensioner degrades to the point of failure, a number of troubling outcomes can result.
If you continue driving with a faulty belt tensioner, your engine’s belt may slip, break, or come off completely, causing immediate loss of power steering, battery charging, and A/C compressor function. Without proper battery charging, you could easily find yourself stranded and needing a tow.
If you don’t want to replace your vehicle’s faulty serpentine belt tensioner yourself, you should make an appointment with a trusted automotive service center as soon as possible. You should only drive the affected vehicle as far as necessary to reach the repair location.
What Causes the Tensioner to Fail?
A serpentine belt or drive belt tensioner can fail for a number of specific reasons. However, the most common culprit centers around standard wear and tear. Over time, the tensioner’s springs and bearings can wear out, putting increased strain on the entire tensioner. This, in turn, accelerates further wear, until failure ultimately occurs.
Another cause of serpentine belt tensioner failure is the misalignment of a tensioner pulley or that of various pulleys within the drive belt circuit. It’s critical that all pulleys/components driven by your vehicle’s serpentine belt are true to one another, in terms of alignment. If they are not, increased bearing wear and eventual failure will result.
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