, Salem, MA


January 26, 2013

Auto Scanner: Vacuum leak could be causing whine in GMC

Q: I have a 1998 GMC Sierra K1500 with 168,000 miles. It has a low-pitched whine like a blower motor might produce, but it is not the blower motor. Under the very slightest acceleration, in drive or neutral, it goes away. It is not affected by engaging/disengaging the A/C compressor. I have replaced both the belt tensioner and the idler pulley to no avail (both were well on the way out). The alternator was replaced about 10,000 miles ago with one that was rebuilt for Delphi. The water pump (Airtex, I believe) is about 30,000 old, and the power steering pump is original but does not whine under load. This whine is hard to hear outside of the cab with the hood open. It is really annoying in traffic. Should I remove the serpentine belt altogether and see how it sounds? Any thoughts?

A: I would not be surprised to find a vacuum leak under the hood that is causing this whine/hooting noise. The engine vacuum is the highest when the vehicle is idling. A slight change in the engine load, such as putting it into gear or raising the RPM, will indeed change the vacuum. One common area of noise that you describe is the vacuum rail that is bolted to the exhaust manifold. There is a little check valve on the line that can make just the kind of noise you describe. It may be helpful to smoke the engine to also find the leak.

Q: I own and love my 2005 Ford 500 Limited AWD with 3.0 engine and recently noticed the heated seats work fine and then don’t work at all for a period of time, then work again. Each seat seems to be independent. Example: Driver’s side will work but not the passenger side. The problem is intermittent but mostly negative, and more often they don’t work. Not sure where to start and wonder if this is something I can try to repair, or does it need to be brought to the dealer? Hoping I can troubleshoot myself, being a 75-year-old on a fixed income. Any idea what the cost would be?

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