The function of a serpentine belt is very simple: it transmits engine power from the crankshaft to the driven accessories. Typically, those would be the water pump, the alternator, the AC compressor, and the power steering pump. Some engines have fewer components, while others (such as diesel engines) have more.
The serpentine belt is held in constant tension, allowing it to maintain its grip on the accessory pulleys with the help of a belt tensioner. The operation of replacing a serpentine belt is essentially pivoting the tensioner away and slipping the old belt off, then positioning a new one in its place and releasing the tensioner.
In most cases, it’s an easy operation. Labour is commonly about a half-hour, give or take, on most passenger vehicles and gas-engine trucks. Some diesel engines with a multitude of accessories and difficult access can take as much as 2.1 hours.
Cost of Serpentine Belt Replacement
Below are some of the serpentine belt replacement cost examples for some vehicle models using the average shop labour rate of £70 for non-OEM and £100 for factory shops an hour:
- The 2010 Chevrolet Malibu with a 2.4-liter engine — Labour in this case is 0.7 hours, with a non-OEM belt costing £10 or £25 at dealer prices. The total job cost would be about £60 at an independent shop and about £75 at a dealership.
- The 2007 Volkswagen Jetta with a 2.5-liter engine — Here, labour is one hour, a workshop replacement belt is about £10, or an original belt is about £35. The total job cost would be about £80 at an independent shop or £105 with dealer parts.
- The 2012 Ram 1500 with the 5.7-liter engine — Labour charges here would be 0.4 hours. A non-factory belt is about £15 while a factory belt runs at around £35. The total job cost would be about £45 with the aftermarket part or £65 with the original part.
- The 2008 Ford F-250 with a 6.4-liter diesel engine — Here, labour (by book time) would be 2.1 hours. With a dual alternator option, a non-factory belt is about £35 or £70 through a dealership. The total cost of the job is about £180 at an independent shop or £220 at a dealership. This would be on the costly end of the spectrum.
Of course, the cost of replacing the serpentine belt for both the parts and labour varies everywhere — from region to region and shop to shop. And it should be added that these costs are for the main or primary drive belt.
In some cases, vehicles will use more than one serpentine belt. Usually, the non-primary belt will be smaller and less expensive.
In most cases, if the primary belt is being replaced, it will be recommended to replace the secondary belt as well. The labour time is either included with the main belt or sometimes a small amount will be added to the cost.
How Serpentine Belts Fail
The construction of a serpentine belt is basically rubber over a strong fabric backing. Rubber has very good grip and resilience when it’s fresh, but it hardens and loses those properties as it ages.
Its useful life varies, but inspection at 5 years or 90,000 miles is a common recommendation. On a serpentine belt, the common sign of age-related failure is slipping on the pulleys, which is noticeably noisy. Most often, that’s when a belt gets replaced.
In other cases, the belt doesn’t slip or make noise, but the rubber can start to crack across the ribbed section. It’s a good idea to replace it then.
Belts can also come apart, the fabric backing can tear and shred into the pulleys as the engine spins. Usually, that only happens after the belt has begun to crack. Hence, it’s a good idea to replace a cracked belt.
What Else Can Go Wrong?
The belt tensioner is usually checked when the belt is off. These have an internal spring (or sometimes, an oil-charged mechanism) that holds the belt in tension and should be checked for smoothness of motion and even tension.
As the tensioner works, it must move with any irregularities in the other pulleys, and this constant motion can cause wear in the tensioner housing. This can be checked for play or damage with the belt off.
While the belt is off, it’s a good idea to spin the pulleys of the accessories (and any idler pulleys) to verify that the bearings are smooth. Sometimes a failed belt is caused by a failing bearing, and sometimes what is taken for belt noise turns out to be noise in something driven by the belt. It’s not always possible to verify a problem prior to removing the belt.
Another thing that can go wrong is pulley alignment. If the pulleys aren’t aligned on the same plane, the belt can jump a rib, wear on its edges, or make noise.
Most pulleys will naturally align perfectly if installed correctly, but bearing issues can cause them to misalign. On the harmonic balancer, sometimes the bonding of the outer pulley to the inner machined core can fail, and that also causes a misalignment.
Pulleys can also become contaminated. If there is a leak that has gotten onto the belt, it can leave gummy deposits or even fragments of the old worn belt lodged in the pulley grooves.
It’s always a good idea to check these and clean as necessary to avoid further problems. And, of course, address leaks to prevent a recurrence.
Stretch Belts
This is a type of serpentine belt that is becoming more common, mostly as a non-primary belt on several makes of vehicles. Unlike the conventional serpentine belt, it has a synthetic rubber compound over an elastic core.
The easiest way to identify a stretch belt is that it uses no belt tensioner but uses its own elastic properties to maintain tension.
Stretch belts usually don’t crack or wear as much as a conventional serpentine belt. Sometimes, they have a specification for rib depth, which can be measured with special tools, and the casing can be examined for integrity.
A stretch belt requires a special tool to install and is usually considered “single-use” due to the ease with which it can be damaged. If a stretch belt has to be removed, it is usually recommended that it be replaced.
The lifespan of a stretch belt is estimated to be about the same as that of a conventional serpentine belt. Hence, the usual recommendation is to replace both of them at the same time when servicing a primary serpentine belt on an engine that also has a secondary stretch belt.