Blogs Car Info Our Show Deals Mechanics Files Vehicle Donation

BMW Engine Belt Failure


During a recent service of my 2002 BMW 540i (110K miles) the serpentine belt was replaced. Less than 2 weeks after this service the power steering pulley sheered off from the power steering motor. This caused the belt to fail, the engine to overheat, and other minor damage. I’m still waiting to hear if the engine block is okay after the overheat of the engine. My question is this: Could the replacement of the belt be related or the cause of this failure?

Yes, ti COULD be. If a new belt is tightened too much, it puts a lot of stress on the bearings of the equipment the pully is attached to, like your power steering PUMP… The bearing may seize and the pully can be pulled off the shaft or the shaft may break off. This does not happen frequently, but it does happen.

It is very common for an alternator bearing the fail if the tech has tightend the belt too much. There used to be a test for tightness; midway between the pulleys, push on the belt with your thumb; if you can push it down 1/2 inch, its about right. If you can’t flex it at all, it’s definitely too tight. Flex it a whole lot, and it’s too lose.

What about auto-tension devices that the mechanic is claiming prevents them from tightening the belt too much?

Docnick is right. One of the more frequent causes of early serpentine belt failure is that the belt was installed too tight. The excessive tension heats up the component bearings and causes them to seize. The power steering pump bearings were just the weakest ones in the link.

Some of the tensioners on a lot of different engines use a bolt to make adjustments to the tensioner itself. It’s a good system but not a perfect one. If the tensioner was adjusted too tight it could cause too much tension on the belt.

This car, like most others on the road, uses an automatic belt tensioner. There is no way it could overtightened.

For some odd reason it sounds like there was a problem with the power steering and this is behind the belt failure. It’s also possible the previous belt was failing or slipping due to this problem. New belt, better bite, so the better bite finished off the hidden problem.

The big issue here is continuing to operate the car with a broken belt. Shut it off when the temp climbs and you’re probably ok. Continued driving with the temp gauge pegged out WILL cause engine damage, no doubt about it. The only question is how bad.