What is This White Stuff Under My Oil Cap?

Whenever we perform maintenance checks on our vehicles, we seldom open the engine oil cap. In most cases, we check … Continued

Whenever we perform maintenance checks on our vehicles, we seldom open the engine oil cap. In most cases, we check the level of engine oil via the dipstick on the side of the engine. The only time that we tend to open the oil cap is during a scheduled oil change. This often occurs every 5,000 to 10,000 miles, depending on the age, make, and model of our vehicles. Sometimes, we also top-off our engine oil in between oil changes. It is only during these times that we may notice a creamy, milky white stuff in the oil cap. This begs the question what is this stuff and does it spell trouble for my car?

What Is It?

Whenever vehicle owners see a milky oil cap, the very first thing that they think of is water or moisture mixing with the oil in the engine. This creates a milky white, creamy sludge on the oil cap and the surface of the engine oil port. This is true. However, because of the unique design of the modern combustion engine, water should never mix with the engine oil. Hence, when you notice this frothy white sludge in the oil cap, it should always merit your attention.

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Oil filler for the car engine

Possible Causes

We know that the white stuff forming under the oil cap is a mixture of engine oil and moisture or water. The natural question is how did it get there? Here are some of the most common explanations.

Natural Moisture Buildup

If you live in an area where it is damp and / or cold, there is a chance that moisture will begin building up right inside your car’s engine. If you take a look at your gas emissions, one of the byproducts is water vapor. What this suggests is that you will always have water vapor or moisture in the engine. However, as the engine warms up to its optimum working temperatures, it can help remove moisture buildup through the process of evaporation.

A milky oil cap can develop if you do not drive your car long enough so that it reaches its engine’s optimum working temperatures. If the engine is not hot enough, then it will not be able to evaporate the moisture inside the engine. This leads to the accumulation of the white stuff under your oil cap.

As such, if you are the type of driver who only uses his car for about 5 to 10 minutes at a time, there’s a chance that the engine will not reach working temperature to facilitate evaporation. The same is true if you are driving your car at a snail pace. Compare this to driving 60 MPH for at least 30 minutes on the highway and you will not have any issues with a frothy buildup under the oil cap.

It is also possible that you have a worn-out or damaged oil cap seal. If there is a break in the integrity of the cap’s seal, then it is possible for moisture to enter.

Poor Car Cleaning Habits

Car owners who are in the habit of using high-powered pressure washers in cleaning their engine bay are also increasing the risk of a milky oil cap. High-pressure water spray can force water through the different connections in the car’s engine. This can include the area under the oil cap. It is also possible that water can enter through the air filter housing, the power steering cap, and the engine oil dipstick. The use of degreasers applied in high-pressure form can also exert the same effect.

When this happens, you are increasing the risk of forming a frothy sludge under the oil cap. If the engine bay requires cleaning, it is best to use low-pressure water spray. It is also important to avoid spraying engine seals such as those found in the valve cover.

Blown Head Gasket

The first two causes of milky oil cap are somewhat benign. However, if you have been driving your car in such a way that you optimize its operating performance and still have this problem, then something more dangerous is the possible culprit. The same is true if you’re taking good care not to introduce moisture into the engine during washing. In such cases, there is only one possible explanation why there is a buildup of white frothy sludge under the oil cap: you may already have a blown head gasket.

The job of the head gasket is to make sure that the engine cylinders are able to perform their function in an optimal manner. The gasket forms an airtight seal between the engine’s cylinders and the engine block. It ensures maximum compression so that your engine will be running in a smooth manner. Another important function is to prevent engine coolant or engine oil from entering the cylinders.

If the head gasket gets blown or damaged, engine coolant can leak into the combustion chamber or the passages of the engine oil. It is the latter that causes the milky oil cap.

One good way to check for this is by evaluating your engine oil dipstick. Run your engine until it has “warmed up” to its operating temperature. Check the exhaust if you notice white smoke. Now check the engine oil dipstick. If beads of moisture are present on the dipstick, then you may already have a blown head gasket.

Of course, there are other manifestations of a blown head gasket. You will also see engine coolant leaking below the engine’s exhaust manifold. You may also notice bubbles in the engine coolant overflow tank or the radiator itself. The spark plugs can also develop problems. Your engine will also start overheating.

You can have your engine cooling system pressure tested. This will help confirm if the milky oil cap you see is one of the telltale signs of a serious problem in your head gasket.

If you notice a milky white stuff under your oil cap, it could only be normal condensation that will go away the moment you drive your car. However, it can also be a sign of a more serious problem so it’s best to have it checked by a mechanic.

Sources:

  1. Milky, Frothy Engine Oil: Should I Worry? – Yummy Mummy Club
  2. What Causes Moisture Build Up Under My Truck’s Oil Cap? – It Still Runs