Oil Sludge Causes, Symptoms, And How To Tackle It!

Oil Sludge Causes, Symptoms, And How To Tackle It!

March 27, 2023 0 By CarGuy

Have you noticed some sludge development in your engine oil and you want to learn more about the oil sludge causes? Well, if that is the case, then you are at the right place because, in this article, there will be a lot to cover.

Doing your own research when it comes to a problem with your car is the way to go, always. Always do thorough research before you jump to a conclusion about a certain problem since the problem is not obvious as it might seem. People think, hey I will replace the engine oil, it might sort out the issue.

Well, in some cases, it could actually get things worse if you have extreme clogging in your engine and this could basically clog up all the important passageways and prevent oil flow, increasing the oil pressure to the roof. But more on that, we are going to elaborate in this article.

First, we are going to learn what is oil sludge in general and whether is engine sludge bad. Then we will cover the symptoms, as well as the oil sludge causes, and see more about what could cause this problem. Then, we will cover the diagnostics and how to sort out the problem as soon as possible. So, if you want to learn more, follow along.

What Is Oil Sludge?

Now before we learn more about the oil sludge causes, let’s take a look at what is oil sludge in general. As you probably assume, there are people suffering similar issues and are really new to cars. So, we need to further elaborate more on what is oil sludge in general.

So, what is oil sludge? Well, oil sludge is a gel-like substance that is found in your ICE also known as an internal combustion engine. Wherever is oil, there could be oil sludge.

You probably know what engine oil looks like, it is a brown greasy fluid that basically lubricates the internals of the engine. And this fluid has an equal consistency. This is known as oil viscosity. So, there is a 5w40, 0w20, and so on.

And what happens when you have sludge, is that the engine oil gets contaminated. And this fluid does not keep the same viscosity. The viscosity changes and creates sludge and it also looks pretty disgusting.

This contamination of the engine oil is caused by different factors that we are going to elaborate on in the following chapters when we will discuss the oil sludge causes. The important to note about the sludge is that this sludge can be consistent and also inconsistent.

So, what this means is that the sludge can be present across all the engine oil, or there could be chunks of sludge somewhere around the engine sitting. And this is the important piece of the puzzle that later on we are going to elaborate on more in-depth. Now let’s take a look at a different topic before we learn the oil sludge causes and that is whether this sludge is bad or not.

Is Engine Sludge Bad

So, we learned what is oil sludge and how it is represented. Now before we dive into the oil sludge causes, let’s discuss whether is engine sludge bad or not.

And the short answer is yes, it is pretty bad. This is one of the situations that you definitely don’t want to happen inside your engine.

We are saying this because whenever there is sludge development inside of the engine, there is engine damage as well.

It could be overheating, or it could be damage done to the camshafts, rod bearings, piston rings, and cylinder walls. All, these components can take a toll when the engine is running on sludge instead of proper engine oil.

Contaminated oil is probably the biggest cause of death to an engine besides overheating. So, this is why you should take this problem seriously and whenever you notice sludge, you need to make sure that you sort out the problem as fast as you can in order to avoid permanent damage to the engine.

We are saying this because if you push this engine like this for a really long time, you could basically thrash your engine in 10,000 miles or so. That’s why learn the oil sludge causes as well as the symptoms. And precisely that we are going to elaborate on next.

Engine Oil Sludge Symptoms

Now let’s cover the symptoms before we dive into the oil sludge causes. Knowing the symptoms is always a good idea because there are a lot of people reading still unsure whether they have an oil sludge problem or not. So, let’s cover the symptoms in the following chapters.

1. Oil Light On

The first and most probable symptom that you will get whenever you have an oil sludge problem is the oil light on. The oil light will turn on and you will get information that something is wrong.

Oil Sludge Causes

And what is bad is that whenever you have this symptom, you don’t know that you have oil sludge. It is only visual information that something is wrong with your engine oil and you need to check. The more important is the following symptom which we are going to discuss before we cover the oil sludge causes.

2. High Oil Pressure

The most important symptom whenever you have oil sludge is probably the oil pressure gauge. And specifically, whenever you have a problem with oil sludge, you basically have a very difficult oil flow.

So, whenever the oil flows really hard, the pressure will increase. The normal oil pressure is somewhere between 20 and 60 PSI. But whenever there is an obstruction in the oil passageways like in this case, you will have high oil pressure.

So, if your oil pressure is always 60 or higher, you definitely have an obstruction somewhere in your engine and you need to do an oil change. But should you do an oil change if the problem is too big? More on that, we will cover it in a bit after we discuss the oil sludge causes.

3. Oil Thick In Consistency

The next symptom in our list is the situation when you notice the sludge. Let’s say that you do an oil change or you checked the dipstick and you noticed that there is a sludgy mess around the dipstick.

This is a dead giveaway that you have a problem with sludge. Usually, engine oil at normal temperatures should be relatively thin, and if the engine is hot, it should be even thinner.

So, if you notice that the engine oil is extremely thick and almost black, or some really light brown color, it is important that you react immediately in order to solve the problem on your car. But more on that, we will cover in a bit after we discuss the oil sludge causes. Now let’s cover the last two symptoms.

4. Engine Is Overheating

The next symptom in our list before we cover the oil sludge causes is the situation when your engine is overheating. But why is this the case?

Well, this is the case because the engine has obstructed oil passageways. And if this happens, there will be less oil flow around the engine.

So, whenever you have obstructed oil flow, there will be hot spots and cold spots around your engine. Making the problem even worse because the metal is simply not exposed to the same temperatures.

And these poor thermals can irreversibly damage the engine and cause the head gasket or oil pan gasket to fail in the process and completely overheat the engine in the process. Oil flow is key when it comes to preventing engine damage from happening. But what are the oil sludge causes? More about the causes, we are going to elaborate in a bit.

5. Poor Fuel Economy

The last symptom that we are going to cover when it comes to engine oil sludge is poor fuel economy.

Whenever you have a situation like this in your engine, you just cannot expect the engine to be as fuel efficient as possible, the engine will require major work in order to resume proper working order. But more about that we are going to discuss more after we learn about the oil sludge causes.

Oil Sludge Causes

We covered the engine oil sludge symptoms, now let’s take a look at the oil sludge causes and see what is causing this problem in your engine.

We will cover all of the possibilities of why this could be the case. So, pay attention thoroughly because there will be a lot to cover on this topic.

1. Bad PCV System

The first and most common in our list of oil sludge causes is the PCV system. The PCV system is basically the positive crankcase system.

This is a very simple system that has the task to remove the pressure from the crankcase and divert these gases into the intake manifold in order to burn.

This is a really essential thing since there is a lot of pressure buildup inside of the engine, known as blowby. And a lot of engines failed or blew seals because this pressure couldn’t be relieved. This is why engineers have invented this system that works with the help of a vacuum.

When the pressure level is met, the PCV valve located on top of the valve cover will activate and release the gases into the intake to burn.

What happens is that sometimes this PCV valve can fail and cause your engine to run poorly and develop issues. And one of these issues is oil sludge development. So, if you have oil sludge and you are doing your maintenance correctly, checking the PCV valve first is the way to go. Now let’s continue with the rest of the oil sludge causes.

2. Coolant Contamination

The second in our list of oil sludge causes is oil contamination. So, what is oil contamination? Well, as we mentioned in the previous chapters, engine oil can be contaminated and turned into a sludgy mess.

One of the biggest contaminants is probably engine coolant. Engine coolant can be really detrimental to the engine oil. For example, the engine overheats and the head gasket fails. Then a little bit of coolant can sip into the engine oil and contaminate it. Slowly, it will turn the engine oil into sludge.

Another way oil can be contaminated is if water enters the engine. For example, if a car was flooded. This would basically turn the engine oil into sludge.

Other ways of contaminating the oil are metal contamination, metallic particles can combine with the engine oil and contaminate it. As well as some other materials like rubber or paper gaskets that are found around the engine. Overall, these are the major reasons for oil contamination and one of the most probable oil sludge causes, now let’s move on to the next possible cause.

3. Low Oil Level

Third, on our list of oil sludge causes is the low oil level. So, why the low oil level is one of the prime causes for this situation in your engine?

Well, the lower you run your engine, the more the engine is overworked. And when your engine oil is overworked, it starts to cook off. And eventually will burn.

Once the oil is burnt out and is all black, it will slowly turn into sludge and will start to stick around the engine and cause a sludgy mess. Now let’s continue to the next in our list of oil sludge causes.

4. Poor Maintenance

The next in our list of oil sludge causes is poor maintenance and negligence. There are a lot of people who are simply negligent and do not follow the recommended intervals when it comes to doing the oil change.

So, people change the oil at 15,000 miles or more, instead of changing the oil at 6,000 as it should be done.

So, every delayed oil change creates a problem, it will clog the oil passageways, it will start to clog the piston rings and they will eventually stop sealing well.

And lastly, it will start to damage your rod bearings and the engine will stop working. It will either spin a bearing or simply seize the crankshaft. Overall, after this type of damage, you can simply throw the engine in the trash can and replace it with a new one. Now let’s move on to the last in our list of oil sludge causes.

5. Bad Engine Design

And the last on our list of oil sludge causes is bad engine design. So, how a bad engine design could affect this problem?

Well, a poor design is not the prime cause of oil sludge. These engines have good oil flow in most cases. But what they do not tolerate is delayed oil changes as we mentioned previously.

So, with each delayed oil change, you will add more sludge and eventually completely clog up the oil passageways.

And eventually, when the oil sludge is too much, there will be increased heat and wear on the elements inside of the engine. That’s why we recommend that if you have an engine susceptible to creating sludge, it is best to do an oil sludge treatment. And more about that, we are going to cover more in the following chapter.

Oil Sludge Treatment

There are a lot of solutions that you can get to clean the sludge. Namely, products like Seafoam that a lot of people are using as you can see in the video below.

But the best cleaning method would be to flush the engine oil and then do a few flushes in a short mileage of let’s say 1,000 miles. This will hopefully remove most of the sludge and will wash the engine on the inside.

But this is not a solution for engines with extreme sludge. What can happen is that the sludge can enter the oil passages and completely seize them. This is why in these extreme cases, manual disassembly and cleanup will be needed. You can also try a special solution called BG Dynamic engine cleaner to remove this sludge. More in the video.

And the last solution is cleaning the block in a parts washer and then doing some machining work, and completely reassembling the engine. And this is a very time-consuming and laborious process.

Especially if it is a work truck. You can get a crate motor for $5,000 and replace this junk engine. That’s our two cents. If it is too expensive to fix, it is a better thing to go for something new. So, we covered the oil sludge treatment and the oil sludge causes, now let’s discuss the cost of doing all this work.

Engine Sludge Removal Cost

We covered the oil sludge causes, now let’s see the oil sludge removal causes. How expensive would be to remove the sludge from your engine?

Well, a Seafoam can cost less than $30. You can give it a try and see if it works. But remember, these solutions are a last resort.

A few quick oil changes to clean the engine will probably cost you a few hundred dollars. And this is a good thing. Also, if you are good when it comes to working on cars, you can try cleaning them manually. At least the engine heads.

But if you do this professionally at the shop with disassembly, cleaning, and machine work, this would easily cost you about $2,500 or even more. That’s why we recommend getting a crate engine instead of spending all this money on a sludgy mess.

How To Prevent Sludge In An Engine

We learned the oil sludge causes, now let’s take a look at how to prevent oil sludge in an engine. What you can do about this problem?

Well, what you can do about this problem is to do your oil changes regularly. Every oil and filter change is a blessing for your engine. That’s why never skip your oil changes and never leave your engine low on oil. This way, you will be sure that there will be no major problems.


In this article, we focused on the problem of oil sludge inside the engine. First, we learned what is oil sludge and whether or not this problem is serious.

Then we covered the symptoms of oil sludge, as well as the oil sludge causes. Then we learned what you can do about this problem, the causes, and how to prevent it from happening.


How Do You Stop Oil Sludge?

The only way to stop oil sludge is by flushing the engine oil on a more regular basis. The more frequently you do the oil changes, the less sludge will be and slowly all of the sludge will disappear. Even though some engine designs are susceptible to building sludge and there is hardly anything that you can do to prevent this from happening.

Can Oil Sludge Be Fixed?

Yes, there are washing detergents that you can use. You flush the engine oil with this new special oil that will wash the engine internals and once you drain it most of the sludge will be gone. You can also try to do more frequent oil changes. Cut the service interval for a few thousand miles and your engine will be a lot cleaner.

Can Frequent Oil Changes Remove Sludge?

Yes, this is a good tactic to remove sludge in engines that do not have a lot of sludge in them. If the engine has too much, you will have to use a special solution to remove this sludge since this debris is stuck to the engine internals, and is rather difficult to remove it by only doing an oil change.

What Happens If Your Oil Is Sludge?

There will be increased friction inside the engine. Engine oil lubricates the engine and dissipates heat out of the engine. When you have sludge, you will have an engine that will create friction and will wear out prematurely, and will also run hot because there will be nothing to dissipate the heat. So, removing the sludge is important if you want to have an engine that will be good in the long run.