What is this white stuff under my oil cap?

When you do your routine oil change, it is important to remove the oil cap. At this time, it’s wise to perform a quick inspection to ensure everything looks right. If you notice white stuff or milky oil under the oil filler cap, it’s possible there’s a sign of trouble, but it could also be harmless.

We will be breaking down the potential effects of milky-white substance. We also examine if it’s anything you need to worry about. 

Índice de Contenido
  1. What does it mean to have a milky or shiny sludge underneath the oil cap?
  2. Why White Oil Filler Caps Buildup
    1. 1. Moisture/Condensation Buildup
    2. 2. Poor Cleaning Habits
    3. 3. Head Gasket
  3. Solutions for white buildup under oil cap
    1. 1. Drive Longer
    2. 2. Keep your Engine Clean
    3. 3. Repair Head Gasket

What does it mean to have a milky or shiny sludge underneath the oil cap?

It is possible that the oil has become milky or white due to moisture. The liquid turns to a white, sticky substance that sticks on the cap. Water shouldn’t enter the engine or mix with the oil, so it should lead to a closer inspection, but you may not need to worry. 

There are legitimate reasons that water got into the engine that won’t lead to a major repair. A blown head gasket is the biggest problem and will require an engine replacement or rebuild. 

Why White Oil Filler Caps Buildup

1. Moisture/Condensation Buildup

You may find moisture in the engine's combustion chamber if your area is subject to cold or damp conditions. This condensation can be seen first by inspecting the exhaust. It will produce water vapor. 

Many people mistake a milky oil cap with a blown head gasket, which could be true, but the majority of times it’s just normal condensation.

This moisture must be removed naturally as the engine heats up. Once the engine runs at its optimal temperature, evaporation should take place. If you aren’t driving your vehicle long enough for the temperatures to rise this high, the water can’t be burned off. What’s left behind is an accumulation of white gunk under the oil filler cap.

2. Poor Cleaning Habits

Do you use high-pressure power washers for vehicle cleaning? You might find milky oil underneath the engine bay cap if you are using the same pressure washer that you used to clean the engine bay. 

The high-pressure spray can push water into the engine, where it doesn’t belong. The oil filler cap can be clogged if water is mixed with the oil. It can also get infiltrated the engine oil dipstick or the power steering cap. 

3. Head Gasket

This is the issue that no one wants. If you are sure that nothing external or bad practices aren’t causing the milky white substance, it’s probable that you are dealing with a blown head gasket instead. 

It serves a very important purpose. It’s designed to keep the cylinders behind an airtight seal for maximum performance. This seal ensures that the cylinders are able to carry out their usual duties. Additionally, it creates enough compression that the engine runs smoothly. The seal prevents coolant from leaking into the engine and oils from combining. 

When the head gasket is blown, the coolant can leak into the engine’s combustion chamber. The coolant can get into the engine's oil passages and build up in the oil filler caps. 

Check the oil dipstick to see if there is a burst head gasket. You can let the car run until it reaches the optimal operating temperature. You may also be able to inspect the exhaust at this point, as a burst head gasket can cause white smoke.

Take a look at the dipstick and see how it looks. You might have an oily head gasket if you only see engine oil. If you see moisture on your dipstick or milky oil on the cap of the oil, it is likely that the headgasket is the issue. 

You should also consider other symptoms of a blown header gasket during the troubleshooting phase. You could have coolant seeping from the bottom of your engine's exhaust manifold. Also, you might see bubbles in the coolant overflow or radiator.

If you keep having to refill the coolant but you can’t find a leak, this is also a top indication because the coolant is leaking internally. If left unchecked, the blown head gasket is going to cause overheating problems since the system isn’t working as it should.

RELATED: 7 Easy Steps to Check if Your Head Gasket Is Blown

Solutions for white buildup under oil cap

1. Drive Longer

If you can’t find anything mechanically wrong, the problem could simply be due to excessive moisture that’s not burning off. This is especially true if you aren’t taking long trips in your vehicle.

The engine temperature will not reach optimal levels if you drive only 5-10 minutes. Evaporation can’t occur, which allows moisture to build up in the engine. This is not only bad for your motor but also causes milky buildup.

The solution is simple and can even be enjoyable. Go for long car rides. You can drive a lot if you are going to be driving for more than ten minutes. Also, you want to drive at a faster speed wherever possible. You will get your engine to warm up quicker if you go 60 mph, compared with driving at 15 mph down back roads. 

2. Keep your Engine Clean

When you wash the car engine, you need to be careful that water doesn’t get into the motor. Before you start, make sure to inspect the oil cap seal. If it is damaged or worn-out, it won’t provide a barrier for moisture, so you should replace it. 

Once you’ve confirmed that the seal is in good shape, you want to spray down the engine bay with a low-pressure stream of water. However, you can use the pressure washer to clean your engine bay. But make sure that it is turned down. Additionally, take care that you don’t spray directly on the engine seals, especially around the valve cover. 

It is best to use a specially designed cleaner to scrub your engine with a brush. Once you’ve removed the grime and dirt, you can use a normal spray of water to simply rinse it off, thereby keeping it protected from the excessive pressure that’s not needed. 

3. Repair Head Gasket

If the head gasket fails, you don’t have a lot of options. Although some head gasket sealers may work, others say they are not recommended. Make sure to do some research before making any decisions. Of course, if you need a new head gasket anyway, it probably won’t do any more damage.

Depending on the type of vehicle you have, the cost for a new head gasket will be between $100 and $300. While this isn’t expensive, it’s the labor that could break the bank. It all depends on which vehicle you have and the place you are taking it to be repaired. You can easily spend between $750-$2,000.

The repair can be time-consuming, and you may not have your car until it is completed. If the vehicle isn’t worth this type of repair, it might be time to start looking for a new car instead.

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