If you check your oil and it has suddenly become milky white, foamy, sludgy, or light brown, then something may have gone majorly wrong. If there is an issue, you’ll probably notice milky oil, which tends to be thicker than regular engine oil, on the underside of your oil cap. Good engine oil develops into this milky mess when it is exposed to moisture, so on a basic level there is an indication that water or some other undesirable liquid has made its way into your oil system.
At worst, this could indicate a blown head gasket. The head gasket keeps your coolant system out of the engine’s cylinders. When it fails, coolant will make its way in and ultimately mix with your oil. Other causes include sludge, which forms in the crankcase when an engine stays idle for a long period and mixes with the oil, and operating a vehicle in a very humid climate. Driving through deep water can also cause this issue. If you have good reason to believe water has made it into your engine, don’t drive your vehicle.
Whatever the cause, milky oil isn’t going to do its job properly. If you leave it in there, it can impact performance, cause corrosion, and damage parts. You should consult a mechanic ASAP, determine the exact cause, and have it fixed. Once the cause is determined, the engine will need to be drained and flushed out before new oil is added.
