What’s that high-pitched whistle coming from my car?

What's that high-pitched whistle coming from my car?
Rob I have a 2004 Volvo XC90 AWD T6 and when the engine is cold, there is a high-pitched whistle for about the first half-hour of driving. If I take my foot off the accelerator to let the car coast, I hear the high-pitched whistle. If I accelerate, the sound either disappears or it’s very faint. Within the first half-hour (when the engine warms up), the sound disappears. I took it to the dealership but it hasn’t been able to come up with an answer. This all started about one year ago. Ken Anderson, Victoria, B.C. I know your patronize is having a bad time with this Ken, but this is easier than it sounds. The symptoms you describe have diagnosed the problem for us.

This is a classical subject of an intake system “ vacuum ” leak. The tip-off is the warm-up period combined with the restrict side. Vacuum, or more accurately, low coerce, is created inside the consumption system of flicker ignition engine. The reason is the accelerator plate. With the strangle closed, air trying to enter the intake ducting to the cylinders, is restricted. This restriction creates a very low pressure ( or vacuum in lay address ) which provides a mean to accept fuel from the fuel injectors and take this mix into the combustion chamber. We need to understand that atmospheric pressure differentials solve in the stick to manner : no matter what the medium – breeze, body of water, oil, etc. – the meaning will constantly move from an area of high pressure to broken pressure. That is, the “ vacuum ” created inside the inhalation system of your Volvo is not actually pulling outside vent in, the outside breeze pressure ( atmospheric pressure ) is pushing vent into the consumption organization. In a by rights serve induction system, which seals out all extraneous air, there will be no randomness or whistle. The strait you are hearing is air leaking across a damaged gasket or a heave sealing surface. With the accelerator closed, or in deceleration mood, the manifold pressure is identical low and if there is a leak anywhere in the induction system that should normally be sealed, you will hear the ( very coarse ) pennywhistle. Opening the strangle to accelerate increases the manifold blackmail bringing this pressure closer to atmospheric pressure. If this pressure differential gear gets close to being equal ( it will never be wholly adequate ), the whistle will stop or lessen.

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The deepen to the noise once the engine warms up suggests that a gasket coat is not mated properly. The heat of the engine expands the metals and plastics that make up the consumption system, thereby changing the relationship between the offending engine parts, which reduces or eliminates the whistle all in all. This could be a damaged gasket or alloy surface and as the coarse alloy used in generalization systems is aluminum, it is easily damaged if careless work is performed in this area. This brings me to a couple of points :

  1. You mention that this has only happened within the last year. Have you had engine work done in this time frame? If work has been done on or around the intake system, it’s possible that something could be damaged.
  2. Is the dipstick fully in its installed position? Fuel injected engines measure every little bit of air entering the engine and the Positive Crankcase Ventilation (PCV) system exposes the crankcase to this intake manifold pressure. The dipstick tube is essentially a hole leading to the crankcase. If the dipstick isn’t fully installed, air leakage past the stick can sometimes cause this whistling effect.

Have your shop try this the future time you take the car in, Ken. Leave it overnight. When the technician starts the engine the following dawn, have him or her squirt water at every gasket seam and connection decimal point in the intake system. If the whistle is caused by an consumption leak, the water will temporarily seal the leak and the noise will stop for that blink of an eye. This is a cheap and promptly method to check for “ vacuum ” leaks, but unfortunately this is followed by the expensive separate – the compensate. however, if the shop has performed a repair this past year, you should be able to strike a “ grace repair ” with the shop – if it wants to keep you as a customer. Send your auto maintenance and repair questions to globedrive @ globeandmail.com

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Category : Car Brakes