M52TU/M54 Serpentine Belts Explained

Two question I am often asked when it comes to the accessory drive of an M52TU or M54 engine are as follows:

  • Do I have a mechanical or hydraulic tensioner?
  • Do I have a centered or offset tensioner pulley?

This quick write up will hopefully make for a great resource for any existing customer of FCP Euro or anybody just casually scouring the internet for knowledge on what they need to order for their vehicle. BMW produced millions of these engines and were used in the E46, E39, E53, E85, E83 platforms in the United States. The good news is all of these engines use the same parts which makes for easy identification.

The serpentine belt drive system on these engines can be broken down between the accessory drive system and the A/C compressor drive system. The accessory drive system drives your BMW alternator, power steering pump, and water pump. The A/C drive system only drives the A/C compressor which is more or less not a critical system. Both the A/C drive system and the accessory drive system have their own tensioner. Only the accessory drive belt differs in the fact that it makes use of an idler pulley. The idler pulley is always an offset pulley in this application. Below is a photo outlining how the setup looks on the engine along with the components equipped:

The idler pulley on this setup will always be offset. The idler pulley is secured next to the alternator and uses one of the alternator mounting bolts. We list this pulley as offset so that it’s not confused with the tensioner pulley. The idler pulley looks like the following:

The accessory belt tensioner on M52TU and M54 engines can either be a mechanical tensioner or a hydraulic tensioner. How can you determine what your vehicle has? You will need to identify it visually. However, you can use either a mechanical tensioner or a hydraulic tensioner. Regardless of which tensioner you use the serpentine belt will be the same. BMW now only offers the hydraulic tensioner which is a superior design. However, you can still get the mechanical tensioner from INA. In the real world the mechanical tensioner is the most cost effective option but the only downside is it needs to be replaced as a whole unit. The hydraulic tensioner has serviceable components and the pulley itself can be replaced. Here is what they look like:

Mechanical tensioner:

Hydraulic Tensioner:

As you can see the hydraulic tensioner and mechanical tensioner look extremely different. You can usually identify which tensioner you have without having to remove any parts. Remember, you can use either tensioner as they will both bolt up the the engine block.

The only component that really has a drastic change believe it or not this the A/C tensioning system. The vehicles are either equipped with a 4 rib or 5 rib belt. On an M54 engines the belt change happens on vehicles produced from 9/2002 onward. The belt changes and so does the A/C belt tensioner. Both tensioners are noticeably different:

A/C belt tensioner used before up to 9/2002:

A/C belt tensioners used from 9/2002:

As you can see the belt tensioner design on the A/C serpentine drive system are very different before and after the production date split of 9/2002. If you do not know the production date of your BMW when ordering these parts you can confirm if it’s before or after the split by confirming what kind of A/C belt tensioner is equipped on your BMW. You can also confirm by looking at whether you have a 4PK or 5PK serpentine belt.

Here are the part numbers you will need on any M52TU engine or M54 engine built before 9/2002:


Here are the part numbers you will need on any M54 engine built after 9/2002:


FCP Euro also has a repair video we filmed on a 2000 BMW 528i which shows how to replace the belts, tensioners, and idler pulley. The process will basically be the same on just about any M52TU, M54, or M56 engine:



Vehicles this applies to:

  • E39 528i - From 9/1998
  • E39 525i
  • E39 530i
  • E60 525i - Up to 2005
  • E60 530i - Up to 2005
  • E46 323i
  • E46 323Ci
  • E46 325i
  • E46 325xi
  • E46 325Ci
  • E46 328i
  • E46 328Ci
  • E46 330i
  • E46 330Ci
  • E46 330xi
  • E53 X5 3.0i
  • E85 Z4 3.0i (2003-2005)
  • E85 Z4 2.5i
  • E36/7 Z3 2.8i (from 9/1998)
  • E36/7 Z3 2.3i
  • E36/7 Z3 2.5i
  • E36/7 Z3 3.0i
  • E83 X3 (2004-2006)

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Topics: BMW

About the Author: Gareth Foley
Gareth is the BMW Catalog Manager for FCP Euro and has been with the company since 2012. Gareth's BMW obsession started with a hand me down E39 528i when he was 17. From this car he learned how to do his own repair work while also learning more about BMW. When Gareth was at CCSU studying Marketing he had the opportunity to go to SEMA with the college car club. This is where he developed his love of the automotive industry. Since joining FCP in 2012 Gareth has sought out to develop one of the broadest and most accurate BMW replacement parts catalog. he can be reached at gareth1@fcpeuro.com