Crankcase Filter – Symptoms Of Clogged Filter

Crankcase Filter – Symptoms Of Clogged Filter

Are you noticing problems with oil leaks coming from the side of the engine and a significant drop in performance? If that is the case, then you are at the right place because you are probably dealing with a bad crankcase filter, this is why we will try to help you out solve your problem.

Having a problem like this can be a really frustrating thing to deal with. Namely, this component is really important when it comes to the proper work of your engine. The engine will perform quite poorly whenever there is a bad filter in your engine.

And what is worth noting is that this problem is mostly affected by diesel engines. More precisely Cummins, Powerstroke, or a Duramax. If you have a problem like this then you definitely have one of these three types of engines. Not that there are no other diesel engines in the US but these are the most popular ones that have the biggest market share. This is why we will focus primarily on these engine makes.

First, we are going to cover what is crankcase filter is and learn more about the basics and its function. After that, we are going to cover the crankcase breather blocked symptoms and learn what can you expect when you are dealing with this type of problem. After this, we will cover the diagnostics process as well as the replacement and the costs involved in this work. So, if you want to learn more about how to solve this problem, follow along.

Crankcase Breather Filter

Now first, let’s cover some of the basics and learn what a crankcase filter really is. I bet that there are a ton of people reading this article who are not into cars and want to learn some of the basics.

Knowing the basics is a good starting point in understanding more complex stuff such as the function of this component and as well as the symptoms that it will produce when it fails. So, let’s get into it.

Before we learn more about the filter, we need to understand what is a crankcase first. What is a crankcase and why it is so important?

The crankcase is the compartment in the center of the engine block where the crankshaft is located. Basically, the crankshaft is mounted to this crankcase and it rotates inside it. Thus, allowing the engine to produce power.

But as you probably are aware, engines are not sealed inside and engines need to breathe. The block has to breathe in order not to fail prematurely. And if you own a car you are probably aware of the PCV system.

This PCV system is one of the most essential systems in your gas-powered engine that allows proper ventilation inside the crankcase. Diesel cars on the other hand do not have these systems since they do not produce sufficient vacuum. This is why they are only using a crankcase breather filter.

This is a special filter that is mounted on top of the valve cover and allows the extra pressure inside of the crankcase to be re-routed into the intake manifold and help the engine breathe better. But what this breathing means when it comes to the crankcase filter? Let’s further explain this in the following chapter.

Why The Crankcase Breather Filter Is So Important?

So, why is this crankcase filter so important? Well, this filter is important because as we mentioned previously it allows the excess gas to escape into the atmosphere.

If you didn’t know, when the crankshaft spins inside of the crankcase, it moves the pistons up and down.

As the pistons are moving up and down the piston rings collect some of the air that is inside of the combustion process and move it down into the crankcase.

This situation is also known as a blowby. So, imagine that these pistons are constantly collecting fumes into the crankcase and this is not regulated. If this type of work continues for a long time, your engine will probably be destroyed.

And we are serious about this, the pressure that will be built up inside of the crankcase will be so large that will try to escape somewhere and if the filter is clogged up, this pressure will blow some seals around your engine and cause major problems. Or possibly, even crack the block and cause a catastrophic engine failure.

This is why you need to understand the importance of the Cummins ISX crankcase filter. And frankly, for a cheap crankcase filter, you don’t want to take your chances and potentially ruin the engine in the process.

A ton of diesel owners are not aware of these filters and this is why we needed to clarify some things so, you better understand why this filter is so important and needs to be replaced on your engine. But what is the right interval to replace this crankcase filter? Let’s elaborate more on this in the following chapter in detail.

Crankcase Filter Replacement Interval

Now let’s discuss more about the replacement interval of the crankcase filter, when this filter should be replaced on your truck?

Well, if you have just purchased the truck and you are not aware of its service history. Then we would recommend you replace this filter as soon as possible. Immediately after purchase, you should make a small service on the truck and replace all the essentials.

Namely, the engine oil and filter, air filter, fuel filter, crankcase filter, etc. All these components are expendable and they have to go in order for you to avoid some permanent damage to be done to your engine if you keep on driving it like this.

On the other hand, if you own the truck for a really long time and you have never replaced this filter, then you should replace it.

The 6.7 Cummins crankcase filter should be replaced every 67,000 miles. If you delay this replacement, then you risk some of the symptoms that will often develop if this filter clogs up completely and doesn’t allow the pressure to be released.

Also, for the best performance possible, we would recommend you replace this filter once a year. Especially if you have a work truck that you drive on a day-to-day basis. It is far better for you to do preventive maintenance than to repair stuff when it breaks down.

And when this filter clogs up there will be symptoms that are really challenging and easily could damage the engine in the process. And in the following chapters, we are going to cover them in great detail so you get a better perspective on what kind of problems could pop up when you have a problem with this crankcase filter.

Crankcase Breather Blocked Symptoms

Now as we covered the basics of the crankcase filter, let’s now cover some of the symptoms that you will experience when this component fails on your car.

Knowing the symptoms will help you out when determining if you have a problem with this component or not. This is why we will elaborate on every symptom in detail so you get the right perspective when it comes to tackling this issue on your truck, so let’s dive into the symptoms.

1. Check Engine Light

The first symptom that you will notice when you have a bad crankcase filter if you own 5.9 or 6.7 Cummins is the check engine light.

If you didn’t know, whenever this filter has some sort of a problem on a Cummins, the PCM will detect this problem and will throw the check engine light.

Then you will have to move on from there and diagnose this check engine light with an OBD2 scanner tool. With this tool, you will be able to get access to the PCM and all the codes that are stored in the system.

Crankcase Filter

When it comes to this problem specifically, you will get a code that is defined as P1507 – Crankcase Filter Restriction. This code tells you that there is something wrong with the filter and this filter is due to be replaced.

Or it could indicate a problem with the depression valve. So, you will need to check out this component as well if you have a Cummins. For the depression valve the code is P1506 but still, better check both of these components just to be sure. Now let’s move on to the next symptoms.

2. Oil Leaks

The second most common symptom when it comes to the 5.9 Cummins crankcase breather filter is the situation with the oil leaks.

Whenever you have a clogged filter, this is one of the most common symptoms associated with it. So, why is this the case?

Well, as we explained previously, whenever the pistons are moving up and down, they are dragging some fumes down to the crankcase and there is pressure buildup inside of the crankcase.

So, consequently, this pressure will have to escape from somewhere. And that place would probably be some gasket. The valve cover gasket, the head gasket, the oil pan gasket, and front and rear main seals. All these components can start to leak whenever you have a problem like this with the clogged filter.

So, if you notice oil leaks from the side of the block, you should check if this filter is not clogged up. If it is, replace it before the problem becomes bigger. Also, fix the leaks on time before you start losing a ton of oil from the engine. And not to forget to top off the oil level after fixing these leaks.

3. Cracked Pistons

The next symptom of a bad crankcase filter that we are going to cover is the cracked pistons. So, why is this the case, why do pistons crack?

Well, as we mentioned previously, whenever you have a problem like this there will be an increased amount of pressure that will try to escape between the cylinder walls and the piston.

So, this increased pressure will put a ton of stress on these components, the higher the stress on these components the bigger the risk of cracking on the pistons.

You will not be able to see this symptom though. Unless the engine catastrophically fails and you notice this during disassembly. But still, this is one of the things that you need to worry about when it comes to the clogged crankcase filter. Now let’s move on to the next symptoms that could indicate a need for this filter to be replaced.

4. Oil In Turbine

Another symptom of a bad crankcase filter on a Cummins engine is the engine oil on the intake side of the turbo.

Whenever this filter is clogged up, the pressure will push the oil through your turbo and you will notice a big oil sludge inside of the intake side.

So, if you remove the intake hose, you will notice oil residue before the compressor of the turbo. This is a clear sign that your ventilation does not work well and you need to sort this problem out by replacing the crankcase filter.

What is good though is that your turbo will not get destroyed by this action. But still, there is a space of concern when it comes to this situation. That’s why you better replace the filter as soon as possible in order to avoid some permanent damage inside of the turbine. And when a turbo blows you can expect the bill to be really expensive. Now let’s move on to the next symptom.

5. High Idle

The high idle is another symptom that is closely associated with the crankcase filter CCV. This high idle will be present whenever this component is clogged up.

So, why is this the case, how this filter affects the idle speed of the engine? Well, this filter affects the performance of the engine because the pressure inside the crankcase becomes too big.

So, big that it disrupts the idle performance of the engine and makes it perform quite badly. The idle will be much higher than normal.

If a normal idle is about 800 RPM, with this type of a problem, you can expect the idle RPM to rise to 1,500 or even up to 2,000 RPM.

Frankly, this is too much, and not only an idle issue but all sorts of issues can rise from this. Namely, increased diesel consumption and also poor emissions from the truck. Now let’s move on to the next symptoms that are associated with crankcase filter

6. Decrease In Performance

The next symptom that we would like to cover is the situation with the decrease in performance. So, why will this be the case? Why the performance could drop whenever you are having a problem with the crankcase filter?

Well, imagine that you ate something and you are bloated all day. Your stomach hurts and this affects your problem-solving ability or physical ability to achieve tasks.

And so is the case with this filter, the gases are trapped inside of the crankcase and cannot escape. The engine has a high idle and basically struggles to run properly.

It will underdeliver when it comes to the performance and its work will be really bad. The truck will not want to pull as it used to in the past when the crankcase was breathing properly without any hiccups.

This symptom is a clear sign that you need to check the air filter, the crankcase filter, or the fuel filter since these components clog up and prevent the engine from working properly. They are cheap to purchase. So, you shouldn’t be a cheapskate when it comes to replacing these essential components. Now let’s move on to the last symptom.

7. Black Smoke From Exhaust

And the last symptom in our list of bad crankcase filter symptoms is the situation when you have black smoke coming from the exhaust.

In diesel engines to have black smoke when accelerating is completely normal to some extent. But in this case, when this filter is not in the best shape it is definitely not a normal thing. But why is this the case?

Well, as we mentioned there will be pressure inside of the crankcase when this filter gets clogged up. And this pressure will need to escape from somewhere.

Crankcase Filter

The only place for it to escape would be between the piston rings and the cylinder walls. And in this action, a little bit of oil will be able to get on top of the piston and ignite with the diesel.

This is frankly, the same situation as oil burning. But not because of bad piston rings but because of a bad crankcase filter.

This is why you need to dive deeper into solving this problem and learn how to diagnose if you are having a bad filter on your truck, in the following chapter, we are going to explain more about this procedure and how it is done the right way, so, follow along.

How To Diagnose This Crankcase Filter?

So, how you can diagnose this crankcase filter and determine if it’s bad or not? Well, this actually is very simple to do.

You can rely on the symptoms that we listed above. Especially the check engine light and the P1507 code if you are running a Cummins engine.

The next thing to check are oil leaks from the valve cover or the oil pan gasket and if there are leaks, one of the possibility is that you are having a bad filter.

But the simplest way to tell if you have a bad filter is to try to remove the oil cap while your engine is running.

Just start the engine and leave it to run and build up pressure inside of the crankcase. Then after five minutes or so, try to remove the oil cap from the engine.

If the oil cap is difficult to remove and whenever you remove the cap a ton of blowby pressure releases from the engine, then you definitely have a bad crankcase filter. Just go ahead and replace this component as soon as possible in order to avoid further damage.

Crankcase Filter Replacement

When it comes to replacing this filter, it is really easy to do. The first thing that you need to do is to locate this filter. On the Cummins, this filter is usually located on top of the engine below the plastic cover.

Remove the cover and remove the filter assembly. Then install the new filter and plug it back in as it was previously. Doing this job is dead easy and I seriously recommend it to you as a novice mechanic. Especially if you own a Cummins.

How the procedure is done, you can check in the video that we attached above.

Crankcase Filter Replacement Cost

But what about the costs, how much can you expect to pay to replace this crankcase filter on a Cummins engine?

Well, the filter is fairly cheap, costing about $100 in most parts stores. The labor will cost you between $100 and $150. Overall, you will not pay more than $250 for this job. If you do it at home, it will cost you half the price.

Facts: Crankcase Breather Filters for Cars and Motorcycles

  • The crankcase breather filter, also known as the crankcase vent filter (CCV), is part of a vehicle’s crankcase ventilation system, and it is found in internal combustion engines of certain vehicles, including vintage/muscle cars, race cars, motorcycles, and some diesel engines like the Dodge Cummins.
  • The crankcase system’s purpose is to release excess gas pressure by rerouting it back to the engine or releasing it to the environment.
  • The CCV filter removes oil particles and other debris in the gases while releasing excess pressure to the environment.
  • The CCV filter is located on top of the valve cover or the breather hose connected to the air intake.
  • Symptoms of a blocked CCV filter include high idle, oil leakage, and poor engine performance.
  • Oil leakage is a common sign of a blocked filter because when the filter is blocked, there is a high chance of pressure building up, leading to the gasket and seals blowing up, and oil leaking from the engine.
  • If you notice engine oil coming out of your crankcase breather filter, you may need to check your seals, as worn-out seals can cause oil blowback in the inlet valves, leading to a pressure build-up that pushes oil back to the inlet filter.
  • The cost of a CCV filter replacement varies depending on the car’s model and the material, mounting features, filter design, and other vital aspects of your CCV filter. On average, expect to pay between $60 and $180 for a professional to replace the filter.
  • It is essential to choose a CCV filter that can withstand the extreme pressure inside the engine and one that comes with quality filter components like baseplates and filter gaskets.
  • It is recommended to replace the CCV filter at least at the same time as when you replace spark plugs, as these breather filters can get dirty and clog up fairly quickly.


In this article, we have covered quite a bit when it comes to the crankcase filters. First, we learned what these components are, their function, and their importance.

Then we covered all of the symptoms that are associated with this problem and then we learned how you can diagnose and replace the filter at home using common tools.


Now let’s answer some frequently asked questions.

What Is Crankcase

The crankcase is basically the surrounding of the crankshaft. This is the center of the engine block on which the crankshaft is mounted and rotates when the engine is working.

What Is A Crankcase Filter

This is a special filter that is used on diesel vehicles. It has the sole goal of releasing the pressure gases from the crankcase. Purifying the gases in the process before they are re-routed into the intake manifold of the engine.

What Does A Crankcase Filter Do

This filter is filtering the blowby gases that are collected from the work of the engine. Then these gases are re-routed into the intake manifold of the diesel engine to burn. When the filter gets clogged up, it will start to develop symptoms.

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