Low Compression Symptoms

Low Compression Symptoms – How To Diagnose Low Compression?

Are you experiencing constant stalling on your engine and you are asking yourself if this is one of the low compression symptoms? If that is the case, then you are at the right place because there will be a lot to cover on this topic.

Being properly informed about a problem is a key thing in order to tackle this issue quickly and also quite cheaply. You don’t need to pay thousands of dollars on mechanics for what could be a simple diagnosis and repair of your engine.

That’s why you need to learn to troubleshoot and start doing your own research when it comes to topics like low compression and low compression symptoms that often can happen because of different causes. It doesn’t have to mean that the engine is done and you will need a new engine to fix the problem. And because of this, we are going to help you out with solving this problem on the cheap.

First, we are going to cover what is compression and why it is so important in an internal combustion engine. Then we are going to learn the causes for low compression and the low compression symptoms. Knowing the symptoms will tell you quite a lot about the condition your engine is in. Later on, we are going to learn the diagnosing process and also the repair process and how much it will cost you. So, if you want to learn more on this topic, follow along till the end.

What Is Engine Compression?

Before we delve into more complex topics like the low compression symptoms. Let’s first discuss some of the basics and that is what is engine compression in general. Understanding compression will help you out when it comes to properly diagnosing and solving the problem. If you think that you are well educated on the basics you can jump to the causes and low compression symptoms. If not, keep up with us for a little bit.

So, what is engine compression? Well, in simple terms engine compression is the ability for your engine to run. If there is no compression, the engine will not produce power and the engine will simply stop working.

Yes, but what does all this mean? It means that in each cylinder there should be a well enough seal so the compressed air doesn’t escape.

All pistons and valves need to be air-tight when it comes to sealing if you want a good engine performance. If there is no seal into the cylinder, this will produce something that is known as blowby.

The blowby is common on higher mileage engines. This blowby means that the air that is escaping through the piston rings and then enters the crankcase or escapes through the valves.

The more blowby the engine has, the poorer the engine’s performance will be. Eventually, the engine will stop working or will start to produce low compression symptoms that are really annoying to deal with. But more on that a bit later where we will discuss these symptoms in-depth and learn what are the most common ones when it comes to this problem with low compression.

Causes For Low Compression Symptoms

Now before we discuss the low compression symptoms, let’s first discuss the causes for low compression. Causes need to be understood first before we dive into more complex topics like the symptoms.

Low Compression Symptoms

There are a number of causes for this problem though. These causes can be really simple, and sometimes can be really complex things that fail and cost a ton of money to fix. But more in detail in the following chapters where we are going to elaborate on them in-depth and later we will cover the low compression symptoms.

1. Piston Damage Causing Low Compression

The first most probable cause for low compression symptoms is piston damage. The piston as you know is the component that is most stressed out when you go at high RPMs.

The piston is compressing the fuel and air mixture in the four-stroke process which creates energy and your car gives the ability to accelerate.

So, what happens is that sometimes these pistons tend to develop cracks, and sometimes even chunks of them fall down into the crankcase and even destroy the whole engine.

Whenever a malfunction happens into the system and there is mechanical damage created. The engine will start to perform really poorly with reduced compression and you will start to feel the low compression symptoms.

So, whenever the low compression symptoms happen, it possibly means that there is something wrong with the cylinders themselves and this problem needs addressing. Now let’s move on to the second probable cause.

2. Piston Ring Damage Can Indicate Low Compression

Another most common cause for low compression symptoms is the damage on the piston rings. So, why is this the case, what do piston rings have when it comes to compression?

Well, the main task of the piston rings is to maintain the compression of the engine in check. There are compression rings as well as oil rings on each of the pistons.

With continuous use, these piston rings tend to wear and sometimes even fail completely. Leaving you with low compression and facing low compression symptoms.

This happens in some engines that were poorly maintained and oil sludge has collected on the piston rings. Not allowing them to expand and move. Sometimes they can even break completely and fall into the oil pan.

Whenever this happens, there will be low compression symptoms that you will notice. But more on the symptoms later. Let’s first cover all of the causes when it comes to the low compression problem.

3. Cylinder Walls Wear When Compression Is Low

Another cause of low compression symptoms is cylinder wall wear. This is most common in cars that have bad rod bearings.

What happens is that the piston is losing its geometry whenever the rod bearings are worn. So, when the piston loses the geometry it likes to move around.

The more play in the rod bearings the more the piston is scrubbing the walls of the cylinder. Resulting in engine block damage.

Small wear for 100,000 miles is normal. But if there is a significant edge on top of the cylinder, then this means that this engine block has seen better days and is worn out.

The only way to return it to normal would be to do machine work on it and install bigger rings on the pistons. But more on the diagnosing and solving this problem we are going to cover later in the article after we finish the low compression symptoms.

4. Bad Valves Can Indicate Low Compression

Another probable cause for low compression symptoms is bad engine valves. So why is this the case?

Well, this is the case because the valves which are located on the engine head which is on top of the cylinders are also one of the main factors for maintaining compression in the engine.

The valves are accommodated on the valve seats. In order for a valve to have a proper seal, the seats have to be clean and sealed really well.

Sometimes valves would not seal well, this will result in poor engine work and poor compression.

Valves are known to burn and also some carbon buildup can happen on them and the valve seats, allowing some air to pass and make them not seal well. So, when it comes to repairs, this is the scenario you want. Because it is the cheapest to fix from the bunch. But more on that after we cover the low compression symptoms. Now let’s learn the last probable cause for this problem happening.

5. Blown Head Gasket Is A Cause For Low Compression

Another very common reason for low compression symptoms is the blown head gasket. But why is this the case?

Well, this is the case because the head gasket is a very integral component in your internal combustion engine.

The gasket material is making a proper seal between the head of the engine and the engine block. When this seal fails, everything starts to fall apart.

The most notorious problems are oil mixing with coolant, coolant burning, oil burning, and also low compression symptoms.

When the head gasket fails and this causes the engine to overheat. The temps are climbing and the engine head will bend a little bit.

This bend will allow some of the compression to escape from the cylinders. Attributing to the low compression symptoms that will often happen when the head gasket fails. So, replacing this head gasket will return the engine to proper working order.

This is also a relatively inexpensive repair in comparison to the block and piston damage that we have covered previously. But more on that after we cover the low compression symptoms.

Low Compression Symptoms

We have covered the probable causes for low compression. Now let’s discuss the low compression symptoms.

Low Compression Symptoms

As we already told you, these symptoms greatly depend on what is the real problem in your engine. And based on the symptom that you experience you need to come to a conclusion of what is causing this problem in your car. So, without further ado let’s dive into the low compression symptoms.

1. Check Engine Light Symptom

The first symptom in the list of low compression symptoms that we are going to cover is the check engine light that will often illuminate on the cluster whenever there is a problem with the compression in the cylinders.

As you know, modern cars are all computerized. The ECU is monitoring the work of the engine and adjusts the performance based on the values that it gets from the sensors.

Unfortunately, there is no sensor that is measuring the compression. But if there is bad compression, other sensors will be triggered and will show the check engine light message on the cluster.

If you diagnose this problem with an OBD2 scanner, you will most likely get a message that there is something wrong with the coils and other ignition components. Which in fact is not quite correct. But it is a good lead to dive deeper and diagnose the problem. Now let’s move on to the other low compression symptoms.

2. Engine Misfires Can Indicate Low Compression

The engine misfires are also very frequent low compression symptoms that happen in cars. The engine compression is basically the ability to seal. So, whenever there is no proper seal from the valves there will be unequal explosions inside of the cylinders.

A bad chain of explosions in the cylinders will result in engine misfires. You will notice how the engine will run rough on a particular cylinder and you will experience noises coming from the valve cover. These are the prime low compression symptoms

Another sign of misfires is the pops that come from the exhaust pipe. Whenever there are misfires the pops will be more and more noticeable.

This problem is most commonly caused by bad ignition coils or bad spark plugs. But it also can be caused by valves that are not sealing right. So, if you are sure that the ignition components are working fine, then you should focus on the valves and see if they seal well. Now let’s move on to the following low compression symptoms.

3. Engine Down On Power As A Symptom Of Low Compression

Another in the list of low compression symptoms is the engine being down on power. As you know, compression is the thing that makes the engine feel alive.

Without enough compression inside of the cylinders, the engine will simply produce less power than before when everything was sealing properly.

Imagine that one or more cylinders are affected and this will be quite noticeable if you run a straight-4 engine. If you run a V8 you might not notice this problem that much because there are many cylinders.

But in extreme cases, even V8s are vulnerable to low compression and when the compression gets that low, you will lose power and this will be a big problem because you will not be able to haul or tow stuff with your car. So, keep an eye on these low compression symptoms.

4. Engine Keeps Stalling Symptom Of Low Compression

Another in the list of low compression symptoms is the situation when the engine keeps stalling when under load.

The car might want to start and work smoothly. But as soon as you load the car or accelerate, the engine will shut off itself. This is one clear example of low compression symptoms.

This can also be caused by ignition problems, fuel delivery problems, or problems with the crankshaft positioning sensor. That’s why it is often advised for this symptom firstly to inspect the ignition and fuel delivery and then inspect the car for compression measurements.

Later on, we are going to explain how this problem is diagnosed, as soon as we finish with the low compression symptoms.

5. Engine Doesn’t Want To Start Can Indicate Low Compression

And the last in our list of low compression symptoms is the symptom when the engine doesn’t want to start but it keeps cranking.

This problem often can happen in cars with low engine compression. But what is most important it also happens on cars with a bad camshaft positioning sensor and other ignition or fuel-related issues. So, it is often to diagnose the car for these issues first since they are the most common ones.

Then you can move on to the other possibilities like low compression. When the engine doesn’t want to start and it has poor compression, it means that the engine is pretty much with very poor overall health and needs to be completely overhauled or replaced.

When there is no start issue, the problems are much greater than a bad valve or a blown head gasket. Usually, these are problems with worn bearings and piston rings that have too much play, and basically, the engine is not happy at all. It will not want to start and even if it does, it will shut off soon. So, beware of these low compression symptoms. Now let’s move on to the diagnosing phase and learn how you can diagnose this issue, quickly and effectively.

How To Diagnose Low Compression Symptoms?

Now since we covered the low compression symptoms, let’s discuss how you can diagnose low compression. What is good with this problem is that it can be easily diagnosed.

The only thing you will need will be a compression tester. This device is extremely simple with only a gauge that is connected to the cylinder through a hose. They are also really cheap and you can snatch one for a really good deal on Amazon or at the local parts store.

Then you can use this tool to measure the compression on each of the cylinders. As you know this tool is connected to the spark plug whenever you notice low compression symptoms. But before this, you will need to remove all the coils and the spark plugs that you want to test.

Then you continuously crank the engine until you get a reading. The reading greatly depends on the compression ratio. Diesel engines for example have a much higher compression than gasoline engines.

If you test a gasoline engine, the average compression of a good cylinder is about 100. It can go up to 120 if this is a high-performance car with a bigger compression ratio. Everything below 90 is considered to be a bad compression and means that this problem needs to be solved. But how you can solve this problem based on this measurement and the low compression symptoms? Well, that’s what we are going to cover next.

How To Fix Low Compression Symptoms

Now after we covered the low compression symptoms and the diagnosing process. Let’s discuss how you can fix the low compression on your vehicle.

What is useful to note is that this problem rarely could be solved by an owner. Meaning that this is not DIY-friendly work if you haven’t been doing this before.

If the block itself needs to be rebuilt, you will have to take your engine to a machine shop and let them handle this problem. They will machine the block and bore the cylinders. They will also polish the crankshaft and put everything back together.

Also, if the problem is because of the valves themselves, you will only have to take the engine head to a shop and perform a valve job. In some instances, it is often advised to go for a completely new engine head.

Because they are not crazy expensive and will definitely perform much better than a machined one. And hopefully, you will not experience low compression symptoms anymore. But what is the cost to fix the low compression symptoms? Well, that’s what we are going to cover next.

Cost To Fix Low Compression Symptoms

We elaborated on the low compression symptoms and how this problem is tackled. Now let’s discuss the costs involved in sorting this problem out. And frankly, they are not cheap.

In the best-case scenario if you only need to perform a valve job and replace the head gasket you can pay somewhere between the $400 to $800 range. And considering that a new engine head is about $1,000, going for new is much better sometimes.

Now the second probability is if the engine is worn out and needs an overhaul. This will be very expensive, you will highly likely be needed to pay between $2,000 and $3,000 to sort this problem out.

Low Compression Symptoms

And in these cases, if the engine is higher mileage, it doesn’t worth messing around with it when with slightly more money you can get a used engine that has good compression. So, if this is an engine that is dear to you and if you plan to install it in a classic, maybe it’s worth rebuilding. If not, go for a new one and never experience low compression symptoms again.

Conclusion To Low Compression Symptoms

In this article, we covered quite about the low compression symptoms. Fe first learned what engine compression is and we discussed the causes for bad compression. Which were the piston rings, valves, and other components inside of the cylinder.

Then we discussed the low compression symptoms. We learned that when the engine has low compression, the most common outcomes are poor engine work, lack of power, and inability to start.

Lastly, we focused on diagnosing and solving the problem. As well as the costs involved in properly solving the issue.

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