Piston Slap: Of bad guides and wasted wastegates

Carl writes:

My wife has a 2014 BMW X3 with a 2.0L turbo and 100K miles that has been dealer maintained since new. In the morning when first started, it sounds like a muted diesel engine. It’s difficult to tell if the sound is coming from the lower end or perhaps from solenoids/valves in the emissions system. The sound is more noticeable when cold, but it’s still evident when hot. The BMW dealer said the sound is “characteristic” for the engine. Some posting boards say to use a heavier oil than a 5W30 and the noise will go away. What are your thoughts?

Sajeev answers:

Hi, Carl. It’s generally a bad idea to use heavier oil unless there’s a variance of oil weights listed in the owner’s manual. Odds are the oil isn’t a problem here, as problems that surface upon startup but go away/get quieter as the engine heats up can come from other sources. I found two such things in my research. BMW’s N20 engines have known issues with their timing chain guides and the wastegate on the turbocharger. Both could be applicable here, which means we need to try to eliminate one or both of them.

Let’s tackle the timing chain guides first. Timing chain guides are known to rattle upon startup, and that’s not just a BMW N20 thing. (My 1995 Lincoln Mark VIII has been rattling upon startup for 15-something years and well over 100,000 miles; it’s clearly not the end of the world.) There was a recall on this a couple of years ago; you can learn more about this issue here. I highly recommend asking the dealership if BMW will pay for this repair, and they might make this happen easily since you’ve been giving them a steady flow of cash for regular maintenance items. That’s a much bigger deal these days when seeking goodwill repairs.

So, now let’s look at the possibility of a rattle from the turbo’s wastegate. Getting the dealer to address this might be harder, as I see no recall in the works for that. But when you put the affected parts on a bench, the problem becomes clear.

Although it’s a clear-cut issue, the repair can be dicey. You can adjust the wastegate’s linkage, but that might only be a temporary fix. Depending on how long it’s been loose, there’s a good chance the soft metal bushing that’s part of the wastegate system has worn out. A new bushing is needed eventually: Odds are yours has less play, as all that metal heats up from that toasty little turbocharger.

And apparently the new bushing comes in a nice little kit for your wastegate. Many different vendors sell them, and you can see one type of kit being installed here. These might be of varying quality, so discuss which kit is best with a local BMW-savvy technician who is well-versed in the issue.

It doesn’t have to be at a BMW dealership, but I wouldn’t be surprised if the dealer can do the job for a competitive rate, if you ask nicely for a discount since this is a known flaw. I bet they’ve seen this issue on turbocharged BMWs on a weekly basis, and they know the right bits to install. This is one time the dealer might be even better than an independent mechanic. Of course, that depends on the number of BMW-savvy mechanics around you (North America is such a diverse place, ain’t it?), but I’m digressing … Ask someone trustworthy and familiar with N20 engines about how they’d fix the wastegate rattle.

Be it a bad guide or wasted wastegate, I am pretty confident your problem will be found if you start here. Best of luck!

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