Have you ever topped your oil to find this residue?

Maintenance & Repairs, Preventative Maintenance, Services, Tips & Advice — By on February 11, 2012 9:02 pm

What is the yellow stuff underneath the oil cap?? No, it is not caramel custard that you’ve found – it is condensation build up in your oil that has not been relieved. *Moisture is a natural occurrence in most modern day gasoline engines so do not be too alarmed (* depending on where the vehicle is residing, moisture levels may vary). The “crankcase vent valve system” or PCV system (Positive Crankcase Vent) is designed to relieve the engine of pressure build up. This pressure contains oil vapour, in turn containing moisture which is residing in the engine oil. In warmer weather, this system will work flawlessly – in the cold it is susceptible to getting clogged.

The system tends to get clogged during the colder, winter months where the moisture would build up inside the hoses and valves and condense. This condensation builds up, and preventing the vent diaphragm from opening. The diaphragm inside the vent valve is actuated by intake manifold vacuum pressure, in other words – the more  you step on the gas the more the vent will open. The problem is, the amount of condensation built up is sometimes too great for any amount of intake manifold vacuum pressure to relieve itself and the pressure then builds up in the valve cover and crankcase. The valve cover gasket, and oil filter housing gasket may both blow out causing an oil leak due to varying pressure in the engine.

Replacement of the hoses and valve in the crankcase vent valve system is the only way to fix the problem, but what is to prevent this from happening again? Well BMW has designed a “Cold climate version” of this system that is to be installed at the time of repair. Long term we always recommend post repair guidelines. The guideline would consist of:

  • Warm up the engine upon initial start up, for at least 2-5min (especially if left outside, a few  extra would be in your best interest.
  • Stay on top of your oil changes! Bimmersport Automotive Inc recommends your oil changes to be done at a max of every 5mo/10 000km based on 2000km/mo.
  • Avoid constant short distance driving – if you know the engine will not even reach operating temperature before getting to your destination, try to avoid using the vehicle. Not everyone has big commutes, so offsetting the short distance driving with a nice highway drive a few times a week is good enough.


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