I have milky white oil in the cooling reservoir. The vehicle in question is a BMW 318i and was bought 5 days ago.

What would be the most like cause?

  • Hi and welcome to mechanics.stackexchange. Your question needs a little clarification because it is hard to be understood. – kokobill Nov 22 at 7:35
  • What year is it? Other than the head gasket, a common point of failure on BMW motors that can cause oil and coolant to mix is the oil filter housing gasket. Are there any visible signs of oil leaking on the motor? Note, if the engine has been steam cleaned, I'd be suspicious as to why at this point. – Comintern Nov 22 at 16:36

Welcome to Mechanics SE! A white milky, mayonnaise like substance is indicative of oil and water mixing. This could be down to a failed cylinder head gasket or a failed oil cooler. I'm not sure if your car has an oil cooler but the first thing I'd do would be to have the engine either compression or leak down tested. Either of these tests ought to indicate the condition of your cylinder head gasket.

Textbook root cause nr. 1 would be a damaged head-gasket, other possible issues are:

  • Cracks in the engine head or, heaven forbid, the engine block.
  • Some issues with the oil heat exchanger (if equipped)
  • Issues with the transmission cooler (if equipped)

Either way this is something serious, I would try to rollback the purchase (if possible) or let someone fix the issue (costly).

  • 1
    You've been sold a car with issues @wahed, get your money back ASAP! – GdD Nov 22 at 11:26
  • @GdD that depends where the OP is located. In some countries, things are sold as is and no returns can be made once the sale is complete. It's up to the buyer to ensure what the buying satisfies their needs. – BossRoss Nov 22 at 14:51
  • He can try @BossRoss. – GdD Nov 22 at 14:58

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