Cold Climate Oil Separator Issue

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Vehicles Affected

  • E85 Z4
  • E46 3 series
  • E39 5 series
  • E60 5 series
  • E53 X5
  • E83 X3


All of the above models equipped with the M54 engine could potentially encounter a cold-weather crankcase issue. Oil separator/dipstick guide tube blockage caused by moisture freezing within crankcase vent system. This problem occurs in regions with severe cold weather conditions, causing engine oil leaks, broken valve covers or even complete engine failure.


The cause of this is moisture collecting in the engine oil separator and/or dipstick guide tube. When the moisture freezes, it causes the oil separator to stick in either an open or closed position. If the oil separator is stuck in the open position, it may cause oil to enter the combustion chambers and cause the engine to hydrolock. If the oil separator is stuck in the closed position it can cause high crankcase pressures resulting in excessive oil leakage or broken valve cover.


The repair is to replace the oil separator and hoses with the new insulated style. Clean or replace the dipstick guide tube. Be sure to perform any other repairs that were caused by this issue; for example, leaking or broken valve covers. In some cases where extreme cold weather conditions cause the crankcase vent system to freeze again even with the insulated style, the new dipstick tube will have to be modified.

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