Causes and Solutions To A Milky Residue At The Oil Cap Gaskets

Causes and Solutions To A Milky Residue At The Oil Cap Gaskets

What Is The Yellow Stuff or White Sludge On My Oil Cap?

The yellow gunk which appears on your oil cap is normally caused by short trip driving. As long as you have checked the dipstick and have done a quick check of the valve cover inside comes out when it is clean, you will be in a position to eliminate any problem with the engine. So the yellow gunk should not be a cause of alarm as it is very normal after a short trip driving.

When you see moisture beads on your dipstick and some type of white smoke coming out of the exhaust of an engine which is warm, it can be an indication of a coolant of the head gasket leaking into the system of the oil which is not a good thing. In case it is condensation, then it will be minimal moisture seen in the system and heat can be in a position to help to burn it off.

Why Is My Oil Cap Milky? Main Causes?

Whenever you are performing maintenance checks on your car, you might omit to open the engine oil cap. In most instances, you can check the level of the engine oil through the dipstick on the engine’s side. The only time you could tend to open the oil cap is when you are scheduled for an oil change.

In most instances, this normally happens after every 5000 to 10000 miles depending on your vehicle’s make, age, and model. Sometimes you might just end up topping up your engine oil between oil changes. It is during such times that you might notice that your oil cap has a milky, creamy white stuff. This might lead you to want to know what it is all about and what could have caused it.

What Is The Milky Stuff On The Oil Cap?

Whenever you see your oil cap milky, the first thing that might come into your mind is that moisture or water has mixed with your engine oil. This normally creates creamy, white sludge on the oil cap and the surface of the engine oil port. Which is true. But because of the way the modern combustion engine is designed, it is very hard for the water or moisture to be able to mix with the engine oil. And thus, whenever you notice this white sludge on the oil cap, you will need to give it all your attention and find out what is causing it.

Causes Of The Milky Stuff On The Oil Cap

There are several possible causes of the milky appearance on your oil cap. In most instances, the white stuff which is forming under the oil cap is normally a mixture of moisture or water and engine oil. So the question you should be asking yourself is that, how did it end up there?

1. Poor Car Cleaning Habits

​If you have the habit of cleaning your vehicle using pressure washers which are high powered when cleaning your engine bay, then you will increase the chances of having a milky oil cap.The water spray at high pressure can force water through various connections into the engine of your vehicle. This could include areas which are under the oil cap. It is also possible that the water could be able to enter through the housing of the air filter, the power steering cap, and the oil dipstick of the engine.

The same effect can also be exerted when you use degreasers applied with a form of high pressure. Whenever this happens, you tend to increase the risk of forming white stuff on the oil cap. In case there is a need to clean the bay of the engine, you should utilize a water spray which is of low pressure. You will need to also avoid spraying the engine seals such as the ones which are found on the cover of the valve.

2. A Natural Build-up Of Moisture

​If you stay in a damp or cold area, chances are that moisture will be able to build up inside your vehicle’s engine. In case you observe your gas emission carefully, one of the byproducts will be water.This means that, at any given time, you will have moisture or water vapor in the engine of your vehicle. But as the engine warms up at its maximum working temperatures, it can eliminate the moisture build-up via evaporation.

Milky stuff on the oil cap will develop if you happen not to drive your vehicle for long enough and thus, it doesn’t reach its optimum temperatures to evaporate the moisture in the engine. In the process, it leads to a pile of white stuff under the oil cap.

So if you are the kind of driver who uses your vehicle for 5 to 10 minutes, at any given time, most likely the engine will not reach its optimum temperatures to enable evaporation to take place. The same is also true if you are a driver who drives your vehicle at very low speeds. If you can be able to drive your vehicle for 30 minutes on the highway at 60MPH, you will not have this issue of the frothy build up under your oil cap.

It could also be that your oil cap seal is either damaged or worn out. In case there is a break in the cap’s seal integrity, then it is possible that the moisture will be able to enter into your engine.

3. Blown Head Gasket

​If you have been driving your vehicle in such a way that the temperature has always been to its optimum and still find that there is a milky residue at the oil cap, then it could be something serious. The same applies when you have been taking good care to avoid introducing any moisture to your engine while car washing. If that is the case, the only explanation left for the white stuff on the oil cap is that the head gasket is blown up.

The work of the head gasket is to ensure that the cylinders of the engine are performing their function in a manner which is optimal. It is the one which forms a tight seal between the cylinders of the engine and the block of the engine. It makes sure that there is maximum compression for the engine to run in a manner which is smooth. Its other important function is to prevent the engine oil or coolant from making its way to the cylinders.

If it happens that the head gasket is damaged or blown, there is a possibility of the coolant to leak into the chamber of combustion or the engine oil passage. The latter is the one which causes the oil cap to be milky.

One easy way to check for this is by evaluating the engine oil dipstick. You can run your engine until it warms up to its temperatures that are normal for operation. Go ahead and check the exhaust and see if you will notice any white smoke coming out. Check the oil dipstick of the engine and if you see beads of moisture present on the dipstick, then it means you have a blown gasket and you have to replace it immediately.

When the gasket is blown, you can also be able to observe the coolant of the engine leaking below the exhaust of the engine manifold. You could also observe bubbles in the coolant of the engine overflow tank or in the radiator itself. It is also possible for the spark plug to develop problems and your engine will start overheating.

If the above happens, you can have the pressure of your engine tested. This will help you in confirming if the milky oil cap is a sign that your gasket is no longer working.


1. Can Leaving Oil Cap Off Damage Engine?
There is no harm in leaving the cap off. What could happen is that, if you are driving in a dust storm, there is a bit of dust which can get in but not enough to hurt anything.

2. Can I Take The Oil Cap Off When Hot?
Very possible. You can be able to add oil to your engine while it is hot. The oil which is cold is not going to hurt your engine which is hot. But it is advisable that you check your engine oil when the engine is cold before you start it.

3. What Are The Signs Of A Blown Head Gasket?
The signs include:

  • The coolant leaking from the exhaust manifold which is below
  • White milky oil cap
  • Exhaust pipe producing white smoke
  • No visible leaks but yet the coolant is lost
  • Engine overheating
  • Bubbles in the overflow tank or the radiator
  • Poor or lower power running engine

4. Is This Condensation Harmful? (White Stuff)
Determining the cause will determine if it is harmful or not. It is something which is very common. A weather change from one which is warm, to moist to cold or frost that is repeated (condensation) on the vehicle and regular high points of dew can be able to create moisture to form in the crankcase.

This might end up appearing as condensation in the system of the oil and under the covers of the valve. In most instances, cars are driven for a long period of time to enable the condensation to burn off.

This means that, if a vehicle is not driven for a longer period to reach its optimum running temperature to be able to purge out the moisture and those which mostly sit in the parking can end up accumulating moisture in the oil. When at the end you drive such a vehicle, there is some heat which is generated by the engine during the short drive then it cools. The moisture which is trapped then condensates on the part of the engine which is coolest, the oil cap and the valve cover. When you repeat the short trips, more and more moisture is left on these parts which are cooler.

If for sure what you are seeing in your engine is condensation, then there is nothing to be worried about. All you need to check is your dipstick and your exhaust.

If there are beads of moisture on your dipstick and the exhaust producing white cloud of smoke when the engine is warm, it could indicate that there is a leakage of coolant through the head gasket into the oil system which is dangerous. If that is the case, then you will need to take your vehicle to a professional mechanic for check.

To get the answers, you can use the coolant system pressure test. But in case you don’t see any moisture, on the dipstick and the smoke coming out of the exhaust of a warm engine is clean, then it could just be condensation. Just wipe it off the filler tube and cap and check it again after some few days. In case of it being condensation, then it will produce minimum moisture into the system and it can easily be burned off by the heat from the engine.

5. Why Is There No Oil On My Dipstick?

If there is no oil on the dipstick, you will need to add oil immediately. The amount of oil to add will be determined by the type of engine, age of your car, driving conditions and total mileage.

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