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Ask Your Question2000 BMW 740i
Question: what is causing this noise?
Question
when I start my car throughout the day I hear a heavy knocking sound underneath the valve cover on the drivers side for 3-4 seconds. The noise does not persist while I am driving, but it does start again when I start up the car at a later time. The oil has been recently changed, there is no check engine light, the engine is running good, and there is no sludge in the engine. I just bought the car on auction and don't know any services that were performed on the car prior to my ownership. what do you think is wrong with my car? Thank You Mike.
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Answer #1
patrick mannion from Greg Solow's Engine Room, January 24, 2009, 21:37Reply
MasterWhat you describe sounds like classic "tappet" noise. Your description of the noise only lasting for a while after starting the engine from a cold start condition. BMW have a service bulletin describing this problem and how to check to determine if the lifters are indeed bad. First and foremost I would drive the car and change the oil when it is hot. BMW insist on using 5/30W Synthetic oil, a lot of time lifter noise is attributed to to high a viscosity engine oil, If the engine oil viscosity is to high, the oil takes to long to reach the lifters on a cold start because it is "too thick:. I like a product called Risolene. Substitute it for one quart of engine oil. This product is high detergentcy, low viscosity and may clean out slugged or restricted lifters.
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