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Anyone else noticed 3.5L engine whine?

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monarchd's picture
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I don't know if I've just become hyper-sensitive to the sound, but I've noticed just lately a whine -- I'd almost think it was a supercharger, but of course the 350 doesn't have one -- related to engine RPM. Several octaves higher than the exhaust note, and much louder if I'm stationary with bonnet up (transmission in park or neutral).

I don't think it's related to high revs, because I've heard it as low as 2500. But, of course, I also tend to hear it mostly when there is something nearby for the sound to reflect back from (buildings, parked cars, etc). So it may just be that I started noticing it, but I'd also felt I should ask in case a problem is developing...

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redSLK's picture
Federal Way, WA
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2012 SLK350 Roadster
2013 E350 Coupe
350 engine whine

This sounds to me like the noise the electric radiator cooling fan makes. It will come on when you stop with the engine running and run for a while till the engine coling temp comes back down.

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Well, I don't think so. I've heard the fan many times -- actually thought it was some kind of turbine when I first started hearing and it feeling the vibration through the floor when it spins up to maximum.

But the really important difference is that the fan's action isn't linked to RPM. It will start and stop as necessary depending on engine temp or A/C activity. This sound is directly linked to engine RPM, and I can basically make it happen at will by changing throttle position to affect RPM. It's a mechanical whining shound that really makes me think more of the sound you'd hear from a supercharger or like turbo once it's spools... that sort of whine or resonance.

I've had suggestions on other forum that it could be the water pump, alternator, or a vacuum leak. Another suggested that resonance like that might be caused by fluid obstruction in the engine itself -- which seems less likely to me, but worth considering as a potential symptom.

So, I'm planning to take the car in and do a drive with a tech to see what they think. They might well tell me it's just in my head and ignore the sound... but when I started hearing it when accelerating and just at 2500 RPM I started to get a little concerned. If I'm pushing hard and the engine's up past 5000 RPM, then some engine whine/grunt might be expected.... but at 2500? Hmm...

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I have a 2006 C230 and have the same "whine". I believe it is coming from the alternator. The more electrical load the louder the whine. Before it got hot out I did not have this problem or at least it was not noticable. With the hot weather and AC running and with the engine fan on the alternator is under it's heaviest load. That is when the whine is unbearable.
I've addressed this with my local dealer and they claim ignorance. They tried to tell me it was the oil pump and that it was a normal sound.
I logged on to try to find an answer to the solution and say your post. I'm pretty confident it's alternator whine.

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David Brittain's picture
Folsom, CA
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2009 C300 4MATIC
whine/whistle

I have a 2006 C230 and your comments about the whines caught my attention. I have only 3800 miles on my C230 but it has had what I would describe as a whistle occassionally.

I usually start the car and then get out and open the garage door and let it warm up for a few minutes. While warming up, it will always make a brief whistling sound which lasts only a few seconds. I just related it to its normal warming up process.

It will also make the whistling sound sometimes when driving off, usually at about 20-25 mph and go away if I accelerate a little. I never really gave it much thought and I kind of thought it was related to the warm up and the cold air type intake the car has. In other words, I thought it was just making a little whistling noise as it sucked in air.

If any of you get any more info from your MB service techs please pass it on.

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David Brittain Folsom CA Sacramento Section

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OK. I brought the car in today for a technician to hear it and I totally wasn't hearing things or confusing it with something else. It turned out to be that the bearings in the upper idler pulley were beginning to fail, causing the friction and resonance I was hearing. They replaced the pulley and the noise is gone. Wonderful! And just to see how thorough the technician was -- I understand I lucked out and got a shop foreman, which always helps, here are the notes they entered into the computer to describe what work they performed.

Quote:
CUSTOMER STATES THERE IS A WHINE FROM THE ENGINE STARTING ABOUT 1500 RPMS. MOVING OR STOPPED. SEE ATTACHED EMAIL.
FAULTY, NOISY IDLER BELT PULLY BEARING
RUN ENGINE. VERIFY WHINE NOISE FROM ENGINE.. RACK VEHICLE. R&R GRAVEL SHIELDS. NOISE FROM FRONT OF ENGINE. TO ACCESS, R&R RADIATOR ELECTRIC FAN. USING STETHESCOPE, LISTEN TO WATER PUMP, ALT, POWER STEERING PUMP BEARINGS. NOISE FROM ONE OF THE IDLER PULLYS. R&R POLY DRIVEBELT. SPIN PULLYS. CANNOT DETERMINE NOISE. R&R IDLER PULLYS. SPIN BY HAND. UPPER IDLER HAS SLIGHT ROUGHNESS WHILE SPINNING. REPLACE IDLER PULLY. REINSTALL BELT. START ENGINE, NOISE GONE. REINSTAL RAD FAN. ROAD TEST.
I rather liked the touch of removing the pulleys to spin them to feel how they moved. :D But having this resolved in just one trip (and less than a day!).... priceless! :D :D

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JimDavis MTc320's picture
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Re: Anyone else noticed 3.5L engine whine?

Just addressed similar problem on 06 350 SLK with 12000 miles. Dealer found defective Idler Pulley Bearing. Replaced Sheave Pulley p/n 2722020819. Problem solved.

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