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Mercedes-Benz S420 Idler Pulley Replacement Costs
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5 Symptoms Of A Failing Idler Pulley
Here are five common signs that indicate idler pulley issues:
1. Chirping Or Whining Noise From The Engine
Engine noise due to idler pulleys can be attributed to three possible situations:
An Old Or Worn-Out Pulley: When the pulley starts to wear out, it may make a squeaking or chirping noise due to rubbing against the engine drive belt (sometimes called engine belt or accessory belt).
Pulley Slippage: Once the pulley is sufficiently worn out and starts slipping, you’ll hear a whining or squealing noise that worsens as the damage increases. Pulley slippage can lead to other issues like drive belt and alternator trouble.
Pulley Damage: A worn-out pulley will get damaged and form cracks after a certain point. In that case, you’ll hear an even louder and continuous squealing noise. It may eventually break apart and cause the serpentine belt to tear and break as well.
In other words, the noise from a failing idler pulley will increase as the damage increases. So, it’s best to have the part checked while the pulley noise is light.
2. Illuminated Check Engine Light
Generally, an illuminated check engine light won’t turn on to indicate a failing idler pulley. However, it may turn on due to the effects of a busted idler pulley. What triggers the check engine light?
A broken idler tensioner pulley can cause a displaced drive belt, leading to a series of other issues, including alternator failure. The check engine light would be triggered as soon as the drive belt slips off.
So, the check engine light could be a symptom of a damaged idler tensioner pulley.
3. Reduced Vehicle Performance
The idler pulley is a component of the serpentine belt system that drives important elements like the alternator, power steering (via the power steering pump), and water pump. That’s why a bad pulley will hamper a vehicle’s performance and needs immediate servicing.
Note: Some older vehicles have a separate fan belt and alternator belt rather than a single serpentine belt connected to all the engine accessories.
4. Visible Wear And Tear
A visual inspection of the engine belt, especially if you hear a chirping engine noise, can help you determine if you need an idler pulley replacement.
Look out for abrasions and scoring marks on the pulley or damaged pulley bearings. This wear and tear could eventually lead to pulley seizing or a pulley breakdown.
Alternatively, you could have a mechanic take a look at your engine bay if you suspect pulley damage.
5. Drive Belts Stop Working
A failed idler pulley can affect the rotation of the accessory belt and may even cause the belt to slip off and stop working. So how do you know when you have a faulty drive belt?
Most probably, the check engine light will be illuminated, and you’ll need to inspect the engine. Your car may have a stalled engine with an undone or broken drive belt. But even if the engine can run without the belt, it’ll overheat as the water pump will stop functioning.
How Urgent Is An Idler Pulley Replacement?
A failing idler pulley may affect your car’s performance and your ability to drive it. It can wear down the drive belt or let it slip out of place, creating a host of other engine and electric component problems.
So, it’s best to replace a failing idler pulley at the earliest, as prolonging the issue will only increase the costs and repair parts needed.
Tip: It can be beneficial to have the tensioner pulley, belt tension, and timing belt checked when getting an idler pulley replacement.
How Much Does An Idler Pulley Replacement Cost?
The total price to replace an idler pulley can range between $80 and $200. This range includes the cost of the new part as well as the cost of labor. Typically, the auto parts cost ranges from $40 to $90, and the labor costs about $40 to $110. Moreover, the cost also depends on the vehicle model and parts needed.
Here are a few examples:
For Toyota cars, an idler pulley replacement averages between $175 and $210. The parts can cost about $105 to $120, while labor costs between $80 and $90.
For Honda cars, an idler pulley replacement cost ranges from $253 to $321. The auto parts cost about $135 to $178, and labor costs between $118 and $143.
Tip: If the idler pulley is covered under warranty, you could save costs on the replacement.
4 FAQs About Idler Pulley Replacement
Here are answers to some common queries about idler pulleys:
1. What Is An Idler Pulley?
An idler pulley is a component of a vehicle’s drive belt system that helps the belt function properly. It works with the tensioner, helping guide the serpentine belt as it rotates at high speed.
It helps maintain enough tension to ensure that the belt runs smoothly and doesn’t come in contact with other parts of the engine.
In doing so, the pulley helps power some important engine accessories — including the alternator, AC compressor, and power steering system.
However, it can wear out and eventually need replacement because it’s in constant contact with a fast-moving belt.
2. When Should I Replace The Idler Pulley?
You may need to replace the idler after the car has crossed 100,000 miles. But it can wear down faster depending on one’s driving style and operating conditions.
Also, watch out for odd noises from the engine bay or other pulley and belt tensioner failure symptoms to know when it’s time to replace the part.
3. Can I Drive With A Bad Idler Pulley?
You can drive your vehicle with a bad pulley, but not for long. Depending on the pulley’s condition, the car may run for months or could break down in a few days.
However, driving with a bad idler pulley isn’t worth the risk.
If the pulley and the serpentine belt system are damaged, the belt could break or fall out of place.
This could cause:
A loss in the functionality of the alternator, water pump, air conditioning, and power steering pump
Overheating of the engine, and potential engine failure
So, it isn’t safe to drive a car with a faulty pulley. Calling an automotive mechanic immediately could help you save money on potentially more repairs.
4. How Can I Replace An Idler Pulley?
Here are the DIY steps to replace an idler pulley:
Park the vehicle and let the engine turn cold.
Disconnect the negative battery cable to cut power to the engine. Set the cable aside.
Use a socket wrench or ratchet to release the tension from the belt tensioner pulley, and remove the drive belt. Check the tensioner arm for any wear and tear — to see if it needs to be replaced.
Locate the idler pulley mounted at the front of the engine block.
Remove the retaining bolt (or idler pulley bolt) and then the old pulley. Keep the hardware that comes off with the pulley safe, especially the pulley bolt, as it needs to be reinstalled with the new pulley.
Install the replacement idler pulley and reattach the hardware, including the mounting bolt and any other bolt removed during the replacement.
Use a torque wrench to fasten the idler pulley bolt and the new idler pulley. Ensure the pressure setting matches the measurement specified in the vehicle’s repair manual.
Reinstall the drive belt or put in a new belt replacement if the old belt is worn out. Tighten the tensioner.
Reinstall the negative battery cable.
Note: Your vehicle may have different bolts around the drive belt or a different mechanism to release the tension on the drive belt. Moreover, idler pulleys are involved in many crucial functions of a vehicle. So, it’s best to leave its replacement to a professional mechanic.