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Engine Knocking When Switching to Mobil 1™
 
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Question:
Engine Knocking When Switching to Mobil 1™
I have a 1997 m3 BMW with 120k miles on it. I always used Castrol 20W-50. I switched to Mobil 1™ 0W-40 and my hydraulic valves are knocking. I had to pour out 7 quarts of fresh Mobil 1 and flush the engine. Installed 7 quarts of fresh Mobil 1 0W-40 again and valves are still knocking. I poured that oil out and went back to Castrol 20W-50. The knocking is gone. My problem is that I purchased about 40 quarts of Mobil 1 to switch all my BMWs but now I'm afraid I'll have similar problems on my others: m3, 328, 735 and 325. I have already lost 14 quarts of it and have a bunch more that I may have similar problem with. Please respond with a possible solution. Thanks Dr. Yudin PS. I emailed regarding this to you about a month ago and never received any response.
-- Igor Yudin, San Francisco, CA
Answer:
Mobil 1 0W-40 is fully approved by BMW against the BMW Longlife-01 specification, and as such, is appropriate for use in all BMW engines requiring that level of performance. We suggest you consult your owner’s manual or BMW service for the appropriate viscosity grade suitable for your model BMW. Different M3 model year engines can require different viscosity grades. Regarding the engine noise, moving to a slightly different viscosity oil may not solve this issue. We suggest you consult with your mechanic to ensure there are no underlying mechanical issues.
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