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Q: Engine making weird noises and revving

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When I start up the car, the engine revs up and makes this weird sound. It mostly does it when it is cold outside and not all of the time. The dealership has looked at it three times and can't find the problem. The vehicle also recently issued a loud shriek with the Engine light coming on. The AC has been acting up as well, with it coming out very low and high before eventually kicking in.

A: With these combination of symptoms, it soun...

With these combination of symptoms, it sounds like your car has a drive belt problem. When it is cold outside, there is more load on the belt on initial startup. In other words, the pulleys are harder to turn. When this happens, the power steering fluid is usually thick, the alternator is charging a slightly drained battery, and the AC compressor oil gets thick, too. The Check Engine Light might be a coincidence, but it may also help find the problem. The code will be stored even if the light is off now. The issue you mentioned with the AC is a strong clue as well. If the clutch is weak it may slip and make noise at first. When your heater controls are in the defroster position, or floor and defroster, this automatically commands the AC compressor to dehumidify the air. If the noise happens every cold morning, try leaving your heater totally off and see if the noise stops. If it does, then this could be one explanation for the noise. The belt itself could also be slipping - indicating a worn belt or tensioner. I would think that the dealer would probably have spotted this though. One more possibility is that the harmonic balancer has failed. The pulley that drives the accessories is connected to the crankshaft through a piece of rubber that’s bonded to each piece. The bond can break and it will intermittently slip, usually under heavy load or when it is raining. A qualified mechanic, such as one from YourMechanic, can come and inspect the related parts to determine what is causing your car’s strange noises.

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