Apart from just driving the wheels through the gearbox, it also drives other crucial components like the AC compressor, your alternator, and a couple of pumps. A serpentine belt and a couple of pulleys transmit power from the crankshaft to these components, transferring mechanical power to turn them.
The correct name for the belt is a serpentine belt, but many people call it an alternator belt since the alternator is one of the biggest components it drives.
Regardless of what it drives, the belt won’t last forever, and you’ll have to replace it sooner or later. Ideally, replacing it should eliminate all the slipping and noises an old belt comes with.
You can guess how annoying it would be to still hear the squeal after installing a brand new belt to fix the problem.
Why is My New Alternator Belt Squealing?
If you still get the squeak after replacing any belt on your vehicle, be it the timing belt or the alternator belt, chances are that your new belt is too tight or too loose. Here is a look at what could cause such a scenario.
You Did Not Adjust Tension on the Alternator Pivot
Most vehicles have a pivoting alternator that you can adjust to get the perfect tension on the serpentine or aux belt.
The alternator pivots around a fixed lower bolt in such installations while the top bolt sits in a slot, not a round hole. The position of the bolt in this slot can adjust the aux belt tension or give the alternator perfect contact with a bigger serpentine belt.
- Loosen the bolt on the slotted upper hole
- Twist the alternator towards the belt to tighten it or a bit away to loosen it
- Tighten the bolt again to hold the belt in place
You can use a gauge to check that the belt is at the recommended tension or run the engine to confirm that the alternator runs at the same speed as the belt without squealing. Scroll to the section on how to check a belts tension for more.
Installing a Belt on Dirty Contaminated Pulleys
Alternator belts don’t work well with oil, coolant, or fuel leaks. If any of the pulleys are dirty and have grime on them, clean them first with a degreaser and let them dry before installing the new belt.
Clean pulleys will ensure your belt doesn’t slip. This is a simple and fast way to reduce the chances of a new belt squealing as soon as you put it on.
A Failed or Failing Belt Tensioner
After slipping on a new belt, you have to adjust its tension using some form of the tensioning system. The tensioner will then load the belt to its ideal tension once the engine is up and running.
Spring Loaded Tensioners
These passive tension systems create the right strain on the belt using a strong spring. If the spring loses its holding power or is misaligned, it won’t pull the belt to the right tightness around different pulleys.
A loose spring will make the belt tensioner play around as it runs around the pulleys. The serpentine belt will either pull off or misalign at intervals leading to a screeching noise.
If the spring is too strong and pulls the belt too tight, it could also scrunch up the belt around the pulleys leading to further noise.
A Hydraulic Belt Tensioner
While most vehicles have the simpler and hardy spring-loaded tensioner, others opt for hydraulic-driven belt tensioners.
A failed hydraulic tensioner is most prominent when your vehicle is idling and not creating lots of hydraulic pressure to work the tensioner. Apart from squealing, you will also hear rattling noise and perhaps see leaks on the tensioner.
A Problematic Idler Pulley or Tensioner Bearing
Notice those pulleys on the engine block that holds the belt but do not drive anything? These rollers are either idler pulleys or tensioner bearings.
Tensioners and idler pulleys are common in engines that use a single serpentine belt to drive all accessories and components that need mechanical power.
If one of the pulleys and tensioners fails and snags slightly, they will make a squeaking sound as the belt forces them to revolve. The same noise could happen if the bearings in other driven components are faulty.
The noise could also come from failing bearings in the:
- Alternator
- Power steering pump
- AC compressor
- Water pump
Use a stethoscope to narrow down the noise and identify the problematic component. Alternatively, get a mechanic to help you troubleshoot and identify the faulty component.
A Misaligned Belt or Pulley
With so many pulleys to thread your drive belt through, there’s the possibility of misaligning a belt, a pulley or connecting multiple belts incorrectly.
Different vehicles have different alignment and installation order recommendations. Consult your user manual and ensure that you install the belt in the correct order.
Even if you get the order right, the belt could still squeal if it is misaligned. Ensure that the grooves on the belt perfectly match those on the pulleys. This will make the belt run silently and give it a longer lifespan.
Installing the Wrong Belt
Using a smaller than recommended belt, a bigger belt, or a low-quality belt that isn’t strong enough could make a whirring noise. The same will happen if the groove patterns don’t match and your belt remains misaligned.
If the belt is still squealing after confirming that it is not too tight or too loose, you purchased the wrong belt.
The Belt is Just Cold
Very cold belts squeal way more. It will reduce the noise and even go silent when the engine runs and the friction warms it up.
How to Diagnose an Alternator Belt Squeal After a Replacement
While trying to fix all the above problems is a good way to sort all issues related to your serpentine belt preemptively, you can make things simpler and more precise using the following troubleshooting steps.
- Turn off the engine inspect the belt. Ensure that it’s perfectly seated and all the grooves are well aligned
- Turn on the engine, and with the belt squealing, spray it with some water or WD40. If the noise persists, the problem should be a bad pulley, tensioner, or driven component bearings. If it goes away, the belt is too tight, loose, or misaligned
- Get the engine idle and inspect if the tensioner and pulleys are running straight and not sideways
- Inspect individual pulleys to check if they have too much play. The pulleys can wiggle a bit, but too much play will throw the belt’s tension off, leading to unexpected slippage and the annoying squeal.
How to Use a Ruler to Check a Belt’s Tension
Generally, your serpentine and aux belts need to be tight enough to transfer power but not too tight to pull pulleys off alignment. As such, many engines don’t have a tension gauge.
If your vehicle has a tension belt monitor, you can use its readings to establish when the belt is tight enough.
- Use a ruler to measure between the two furthest pulleys in the assembly and identify the midpoint
- Pinch the belt between your fingers and move it back and forth
- If it is tight enough, you should get half an inch of play in both directions
- If you get more, you will have to tighten the belt
- If you get less, the belt is too tight, loosen it
While this is a standard for most vehicles, consult your user manual for specific instructions on how tight your serpentine belt should be. If the guidelines exist, they should override this generalization.
How Do I Stop My Aux Belt From Squealing?
The aux (auxiliary belt) drives the alternator and a few more components in engine setups that don’t use one long serpentine belt.
If your aux belt is squealing, chances are:
- It is too tight
- It is too loose
- It is misaligned
- You used the wrong replacement belt
- The bearings on related pulleys and the alternator could be failing
Follow the troubleshooting procedures we have listed above to narrow down the problem and identify what you should deal with to remove the noise.
Can I Still Drive With a Squeaky Serpenting Belt?
Driving the first few days after noticing the problem shouldn’t cause a problem. However, the squeal robs power off the belt, and it doesn’t drive the necessary components well.
This means you could starve your vehicle of crucial support ranging from:
- Electricity if the alternator isn’t spinning fast enough
- Coolant if you have a belt-driven water pump
- Cooling if you have a belt-driven fan
- AC when the belt can’t drive your AC compressor well enough
These shortcomings will result in problems like an overheating engine, overheating while idling, an undercharging alternator, and AC that doesn’t get cold.
Though some are mere nuisances, an overheating engine could lead to cascade failures affecting things like your head gasket and even the crankshaft position sensor.
Be wise. Sort out your serpentine or aux blets as soon as you hear them squeak. You’ll save money and time in the long run.
What Will Happen If My Alternator Belt is too Loose?
If your alternator belt is too loose, it will slip when the alternator is fully loaded. The slipping means the belt won’t transfer enough mechanical energy leaving your alternator spinning at lower than ideal RPM.
As a result, the alternator will not push out peak power, and the failure could lead to a drop in the 12V rail if your battery is already too low. Otherwise, it will force the battery to pick up the slack and could drain it if the problem persists.
Other than this, a slipping belt wears out faster since it encounters more friction. It will also rattle and squeak as it spins.