Mercedes-Benz Serpentine Belt Replacement 3.0 Diesel Engine

Is your Mercedes-Benz engine’s squealing sound, A/C, and power steering not working correctly? Learn how to fix the problem by replacing the serpentine belt of your Mercedes-Benz.

This guide provides instructions on changing the serpentine belt on most diesel Mercedes-Benz vehicles, including the E-Class, C-Class, CLK-Class, ML, GL, R-Class, and Sprinter equipped with the 3.0 diesel engine, OM642. It is generally applicable to models that end with 320 CDI or 350 BlueTec. Replacing the serpentine belt on a Mercedes-Benz 3.0L diesel engine is relatively easy and takes about an hour.

Symptoms

Common symptoms indicating a problem with your Mercedes Benz serpentine belt include:

• Whistling or squealing sound in the front end of the engine.
• Wear and cracks in the belt.
• Components like AC and power steering are not working correctly.

What you will need

Parts

• Mercedes-Benz Serpentine Belt OM642

Tools

• E-10 Torx socket
• 17mm socket
• 8mm combination wrench
• Flat screwdriver

Procedure

Follow these steps to change the serpentine belt on a Mercedes Benz 3.0L engine.

Removal

1. Park the vehicle on level ground and let it cool down. If the engine is still hot, you risk getting burned.
2. Pull the hood release under the dashboard and open the hood. Secure the hood with the hood support.
3. Remember to disconnect the battery’s negative terminal every time you work with your serpentine belt to prevent accidents or damage to you and some of the vehicle components you are working with.
4. To disconnect the lower intercooler hose, use a flat screwdriver, slide the metal clip off, and then push it down and separate it from the upper hose. Once the hose is disconnected, you can remove the Torx bolts of the noise-damping hose using an E-10 Torx socket, but if it is not available, you can also use an 8mm combination wrench or 8mm socket. After removing the two bolts, one metal plate still holds the hose. Remove the screw, remove the metal plate, and pull the hose out.
5. Before removing the serpentine belt, take a clear photo or draw the belt’s routing pattern to the pulleys; this will serve as a reference when installing the new serpentine belt.
6. Removing the serpentine belt requires you to access the belt tensioner; remember, you do not have to remove the bolts of the tensioner because you are just replacing the belt. You need to use a 17mm socket and place it on the tensioner’s service bolt, push the handle down counterclockwise, and slide the belt off. You can now separate the belt from all the pulleys it serves.

Installation

1. Using the photo or drawing of the belt’s routing pattern you made earlier as a reference, start placing the belt on the pulleys. Ensure that the belt is seated correctly on each pulley because if not, the length of the belt may become a little bit short. It will not give you enough length when you try and place it on the tensioner. Place your 17mm socket to the service bolt, push the handle counterclockwise, and slide the belt in. Slide your fingers to each pulley to double-check if the belt is seated correctly.
2. Clean and install the noise-damping hose, place the metal plate properly, tighten the screw, install the upper and lower bolts, and tighten it to its specified torque.
3. Reconnect the lower intercooler hose and fix the metal clip to lock; push it down to ensure it is properly connected.
4. Install the battery if disconnected.
5. Start the engine and verify the fix.

How much does it cost to replace a Mercedes Benz serpentine belt? 

• The average cost to replace a Mercedes Benz serpentine belt at a repair shop is between $100 and 250. Labor costs are estimated between $80 and $150, while parts are priced between $22 and $90.

How often do serpentine belts need to be replaced?

• On average, the Serpentine Belt is supposed to be replaced every 60,000 to 100,000 miles, but you should always follow your car’s service manual for the replacement intervals.

After Installing the New Belt

• Double check the routing against your photo before starting the engine, and make sure the belt sits fully in every pulley groove.
• Make sure the intercooler hose clip is fully seated. A hose that pops off under boost causes a loss of power and a check engine light.
• Start the engine and watch the belt for a minute. It should run straight and quiet with the tensioner arm steady.
• If the squeal returns, check the tensioner and idler pulleys for noise or wobble.

If you get a limp mode or boost related check engine light after the job, a scan tool such as the YOUCANIC UCAN-II Pro reads Mercedes engine codes and live boost pressure on supported models, which makes a loose intercooler hose easy to spot.

Check these troubleshooting and repair guides for more help on your Mercedes-Benz.

Frequently Asked Questions

Which Mercedes models use the OM642 3.0 diesel?

It is used in models badged 320 CDI and 350 BlueTEC, including the E-Class, C-Class, ML, GL, R-Class and Sprinter.

How long does it take to replace the serpentine belt on an OM642?

About an hour for most DIYers.

Do I have to remove the intercooler hose?

Yes. The lower intercooler hose and noise damping hose come off to give access to the belt tensioner.

What are the signs of a worn serpentine belt?

Squealing or whistling from the front of the engine, visible cracks or wear, and A/C or power steering problems.

Related Guides

• Mercedes Benz OM642 3.0 Diesel Engine Alternator Replacement
• How to change Diesel Engine Oil on a Mercedes-Benz OM651 2.1L Easy DIY
• Mercedes-Benz GLK Diesel Check Engine Oil Level
• Mercedes-Benz ML, R, GL Class: Replace Serpentine Belt

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