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Friday, August 29, 2014

Doug's Domain

Doug Vetter, ATP/CFI

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June 5, 2004

Oil Service, Rattling Exhaust Fix

You know your car needs a lot of maintenance when, after a mere month or two, you start to "miss" seeing and chatting with your mechanic. But, given my 22000 mile per annum driving habit, it didn't take long to rack up another 4500 miles on the odometer and schedule a visit for another mid-cycle synthetic oil service.

(Image: Catalytic Converters)Over the last few weeks, I'd noted an occasional rattling in the exhaust while idling. The sound was rather faint -- so faint, in fact, that I had to be outside of the car with my ear positioned "just so" to hear it coming from the front half of the car. I figured either a heat shield bracket had broken, or -- worst case -- the catalytic converter core had started to disintegrate.

Fortunately, as I pulled up to my mechanic's bay to say hello, the car was kind enough to demonstrate the malady for him. As usual, his experienced ear didn't take long to confirm my suspicions. An hour later, my mechanic found me and told me that he'd found (and fixed) the problem.

BMW apparently uses a steel wool type of insulation packed between the catalytic converter and the associated heat shield. This insulation is also used at the attachment points of the heat shield to reduce heat transfer into the shield. In the case of my car, some of this insulation had fallen out due to simple wear and tear. This caused the shield attachment point to vibrate against the exhaust pipe and create that distinctive sound.

He outlined three typical solutions for this:

Yea, I know. A decidedly low-tech solution for a relatively high-tech car, but it's safe and it works (and, ummm, it's FREE).

Parts $36, Labor, $36, Total $86. Mileage: 97317.