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Monday, December 17, 2007

Tech Tip Fix: BMW Oil Consumption

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Tech Tip Fix: BMW Oil Consumption Issues on a 2001 BMW 325I 2.5L M54 Engine

by Dave Tidaback, WORLDPAC Assist European Specialist

In this example a 2001 BMW 325I with the 2.5L M54 engine was brought into the shop with a customer complaint of excessive oil use and oil warning light illuminated intermittently during cold weather driving.

Diagnostic Procedures:

  1. Check for excessive crankcase vacuum at idle.

  2. Normal expected values would be about 10 to 15 millibar, this is equivalent to 1/4 to 1/2 inch PSI of vacuum or 3 to 6 inches of water displacement using a slack tube manometer.

  3. BMW recommends using a slack tube manometer for measuring crankcase vacuum. This tool measures the displacement of water measured in inches and works well for measuring very low vacuum.

    A slack tube manometer can be made by using a piece of clear tubing and marking it in one inch increments then forming it into a "u" shape and fill it half way with water. Next, apply crankcase vacuum to one end of the tube. This can be done at either the dip stick tube or the oil filler cap, so an adapter will need to be made.

    NOTE: The dipstick tube will be the easiest to fabricate a connection for. The point here is that the vacuum test set up is sealed to dipstick tube or oil cap tightly so your reading is accurate. Normal reading is between 3 and 6 inches of water.

  4. The common cause for this condition is moisture accumulating in the engine oil separator, hose to oil dipstick guide tube or the orifice in the dipstick guide tube.

    In cold weather this moisture can freeze. When this occurs and the internal valve sticks in the closed position, a condition of high crankcase pressures resulting in valve cover leakage/breakage can occur.

    In cases where the internal valve sticks in the open position a hydro-lock condition could occur resulting in engine damage due to oil being aspirated into the intake.

    Customers should be advised to warm the engine prior to driving during cold weather conditions. In addition, 5w30 synthetic oil should be used in cold weather conditions.

    NOTE: In cases where oil has been aspirated into the intake and burned, catalytic converter and/or Oxygen sensor damage is a very real possibility.

  5. BMW Service Information Bulletin 11 08 03 addresses modifications necessary for cold weather conditions which cause the oil separator to stick due to moisture from blow by gases freezing inside the oil separator/crankcase breather or dip stick hose.

The Service Information Bulletin covers the necessary updated parts that can be installed for use in cold weather climates and will eliminate the moisture collection conditions that cause either oil to be drawn into the intake causing a blue smoke condition as the oil is burned or increase crankcase pressure causing oil to push out of the dip stick tube, oil filler cap area or engine gaskets.

Diagnosis revealed excessive crankcase vacuum was present during cold operation and the Crankcase Ventilation Valve/Pressure Regulator was replaced to cure the condition.

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