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I own a 2003 BMW 3.0 X5 with 80,000 miles. Recently it was at the BMW dealer for service and I mentioned hearing a noise that appeared to be coming from the area of the serpentine belt. The noise occurs mainly at idle and seems to go away after the engine warms up. The mechanic’s write-up states: 79646 NOISY MECHANICAL TENSIONER INSPECTED VEHICLE AND HEARD NOISY BELT TENSIONER. QUOTED HYDRAULIC UPGRADE UNIT. CUSTOMER DECLINED AT THIS TIME. My question is – how difficult is it to replace the mechanical tensioner (with a new mechanical tensioner). Can I do this from the top of the engine, or does this also require accessing from the bottom of the engine? What parts would I need?
A
We do have the mechanical tensioner in-stock. The replacement is pretty straight forward. We’d recommend that you replace the idler pulley and the belt at the same time. Additionally, since you will have to remove the A/C belt in order to remove the main belt (unless you are ONLY replacing the tensioner, not the belt), you may want to service this belt and, potentially, the pulleys.The Bentley repair manual covers all of this in detail. Also the Spring 2007 Fast Times newsletter, which contains an article on replacing the water pump on a late-model 6-cylinder. This will give you an idea of how to deal with the belt and tensioner replacement. You do not have to get under the car unless you are replacing the belt and, therefore, have to remove the A/C belt. In this case, just remove the under-engine splash panel and you can access the tensioner for the A/C belt.
See our Serpentine belt and pulley replacement DIY video. Click HERE.
Bentley manual:
Mechanical tensioner for main belt (comes with pulley):
Idler pulley for main belt (with mech. tensioner):
Main & A/C belt:
Tensioner for A/C belt (mechanical w/pulley):
I have the EXACT same problem with my 2003 BMW z4. I too was told it was the tensioner bearing. Can you help me with the parts and labor needed?
For a 2003 Z4, the tensioner is of the mechanical type (for both the 2.5i and the 3.0i). BMW has discontinued use of the mechanical tensioner and is now installing the hydraulic tensioners. However, we do still have access to the mechanical tensioners, so that you do not need to do the retrofit to the hydraulic system (unless you wish to do so). We would recommend replacing the belt when you replace the tensioner, as the belt must be removed in order to access the tensioner. Additionally, the A/C belt must be removed in order to remove the main belt, so replacing the A/C belt would be wise.
Please check out our DIY video on replacing belts and pulleys.
Click HERE for belt and pulley DIY
The first generation Z4 (E85) also has a lower deflection pulley that runs in the place where the power steering pump would normally be (the Z4 uses an electrically boosted power steering system, instead of hydraulic fluid). Has it been verified that the problem pulley is not this one?
Click HERE for accessory drive belts
Click HERE for belt tensioners and pulleys
Click HERE for Z4 lower deflection pulley
Thank you for the information. I think I will get a second opinion to ensure it is the tensioner and not the lower deflection pulley. I based my conclusion on one opinion and the fact that my car does the EXACT same thing as the original post’s car (squeaks when the car idles and seems to go away after the car warms up).
If it is in fact the mechanical tensioner, what is the average cost for parts and labor. All the belts were changed last year so unless they look bad when we take them off, I should be OK there.
Again, thank you so much for the help!
Ashley
If the belts were replaced last year (but not the pulleys), the belts should be fine at this point. We would recommend replacing all of the tensioner pulleys, since you have to remove the belts to do so. You might as well start fresh with everything and then you won’t have to go into it again for a single pulley that needs replacement, at a later time. Additionally, a failed pulley can cause the belts to shred or come off and then you not only are dead on the side of the road, you may have a larger repair bill due to extra damage from the belts coming apart (like mine did yesterday, on the way to work, due to a seized A/C tensioner pulley).
So…. to recap … your Z4 has: on the main belt, a tensioner pulley (must replace the complete tensioner, since this is the mechanical type), an upper deflection (or idler) pulley and the lower deflection pulley that replaces the power steering pump pulley (on early Z4s with electric power steering). The A/C belt has just a tensioner pulley (mechanical type, again).
Labor will be about the same, no matter how many of the pulleys you replace, since the first step is to remove both belts anyway. I replaced both belts and both tensioner pulleys (which is all my M3 has) in about 1.5 hours …. in the parking lot, here. The parts pricing will be in the links in my previous reply. Please feel free to call our agents at 800-535-2002, if you would like assistance in figuring out just which pulleys you need.
Wow, thank you again…this has been a TREMENDOUS help!
Best wishes!
What size are the bolts that attached the hydraulic tensioner and idler pully to the engine on a 2001 325i (alt/water pump side)? When I tighten down on the bolt I have for a new idler pully, it tighens the pully and I’ve lost the bolt that attaches the hydraulic tensioner.
In the illustration, above:
#7 = M10×25mm – Allen head
#9 = M8×40mm – Hex head
#10 = M8×50mm – Hex head
#11 = M8×105mm – Hex head
#13 = M8×35mm – Hex head w/washer flange
We can order any of these bolts, if you cannot source them locally. Just give our agents a call at 800-535-2002.