BMW Internal Engine Diagnosis: Right About What’s Wrong

September 30, 2015 | By | Reply More

We’ve seen engines torn down when the real problem was in the ignition system, rod bearings replaced when a wrist pin was knocking, valve jobs done when a timing chain was actually at fault, oil pans removed because of a bad oil pressure sending unit, etc.  So, you’d better be very sure you’re right about what’s wrong.  Here, we cover the traditional basics, with a note on VANOS.

More and more, we’re seeing BMWs with hundreds of thousands of miles on their odometers that have “never had a head off.”  Chalk that formerly-impossible longevity up to several factors:  ever-improving designs and materials, better oils and filters, and a precisely-metered fuel mist that doesn’t wash the lubricant off the cylinder walls.

Still, human nature being what it is, and given the incredible number of miles people drive their beloved BMWs, you’re going to be faced with internal engine problems from time to time.  If it’s premature, chances are it’s due to neglected maintenance (who, me?), and sometimes a repair isn’t the right fix; replacement is.  Regardless, whenever you want to find out what’s going on inside that BMW engine, your diagnostic skills are going to be tested.  We hope the following will help you pass.

Comm, eyes, and ears

Nikolaus Otto

Nikolaus Otto, 1832-1891

As with all repairs, careful communication with the customer at the outset is of primary importance, and that’s especially so given the high costs involved in this kind of work.  What, specifically, is the complaint?  Rough idling, high oil consumption, noises, poor performance, and puddles of oil on the driveway are probably the most common symptoms of something amiss in the engine assembly.  Taking a test drive with the car’s owner aboard will help prevent misunderstandings.

An overall visual and auditory examination should come next.  You might see or hear something obvious, such as a crushed exhaust pipe, or a sludge-packed oil filler cap.  This is related to stepping back and taking a comprehensive, holistic view of the vehicle’s condition and “lifestyle” before you jump to any unfortunate conclusions.  For example, we remember having an OHC V8 in our shop with a low-power, rough-running complaint.  The car was in pristine condition otherwise, so we immediately engaged our standard diagnostic mode, neglecting to note the odometer reading.  After wasting quite a bit of time, we finally noticed the mileage – 243,000!  No mystery then that the nylon timing chain tensioning components should have disintegrated, putting valve/crank synchronization out of whack.  Lesson:  Look at the big picture.  Besides mileage, how was it maintained?  Has anybody else ever been inside that engine?  What kind of driving has it been subjected to?  Highway cruising takes a lower mechanical toll than commuting in stop-and-go traffic, or short hops.

A bulletin search is another crucial preliminary.  It would be embarrassing to miss a pattern failure.

The top diagnosticians we know have commented that getting as much information as possible from the full assembly prior to teardown gave them the best chance at locating and repairing


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Category: Engine Mechanical, the bimmer pub

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