When engine compression is low, your car may not run as smoothly as it should. In fact, you may even experience symptoms like poor gas mileage and difficulty starting the engine. It’s important to understand what causes low compression so that you can get your car fixed and running like new again.
In this article, we will discuss the most common causes of low compression in an engine and how to diagnose and fix the problem.
Table of Contents
How Does An Internal Combustion Engine Work?
The four strokes of an engine are intake, compression, power, and exhaust. All four strokes happen in just two revolutions of the crankshaft or one cycle of the piston (up and down).
The intake stroke of the piston starts at the top dead center (TDC). The crankshaft pulls the piston down to draw air and fuel into the cylinder through the open intake valve.
Next, both valves close, and the piston is pushed back up to TDC by the crankshaft to compress the mixture of air and fuel. This increases the temperature of the mixture, making it more combustible. During this stroke, the Spark Plug fires, igniting the mixture and starting the power stroke.
The power stroke is where the piston is pushed down by the expanding gases of the burning air/fuel mixture. This provides the power to turn the crankshaft and ultimately move the vehicle.
Finally, both valves open, and the piston is pulled back up to TDC by the crankshaft to push out the exhaust gases. This is how an internal combustion engine works!
What Happens if Gases Aren’t Properly Compressed in Combustion Chamber?
If gases aren’t properly compressed in the combustion chamber, they can cause several problems. The most common problem is that the engine will run too lean, leading to engine damage.
Additionally, improper compression can cause the engine to overheat and potentially catch fire. Finally, it can also cause the engine to backfire or stall. These problems can be avoided by ensuring that the gases are properly compressed in the combustion chamber.
What Different Engine Compression Issues You Might Face?
There are several different types of low engine compression issues that you might face, these include:
- Low Engine Compression, In One Cylinder
- Low Engine Compression, In All Cylinders
- No Engine Compression In One Cylinder
- No Engine Compression, In All Cylinders
- Low Or Zero Readings, In Two Adjacent Cylinders
Causes of Low Cylinder Compression
Many different things can cause low compression in one cylinder. The most common culprits are:
- Leaking valves
- Worn Piston Rings
- Excessive carbon buildup
- Broken Valve Spring
- Blown Head Gasket
- Broken camshaft
- Bent pushrods
- Broken Timing Belt or Chain
- Hole in Piston
- Bad Intake and Exhaust Valve
- Dropped Valve Seat
- Cracked Cylinder Head
Let us explain these causes a bit:
1. Leaking valves:
If the valves are not sealing properly, compression will escape from the cylinder, causing low compression.
Valves can leak for many reasons, including:
- Worn or damaged valve seals
- Damaged or bent valves
- Worn valve seats
- Excessive carbon buildup on the valves
If a valve is not sealing properly, air will escape from the combustion chamber during the compression stroke. This will result in less pressure being exerted on the piston and thus less compression. Additionally, valves that are not sealing properly can also allow oil and other fluids to enter the combustion chamber. This can cause the piston to “hydrolock” or become seized due to the high pressure of the fluid.
2. Worn Piston Rings:
Piston rings are responsible for sealing the combustion chamber and providing a surface for the piston to ride on. Over time, piston rings can become worn or damaged, causing them to lose their ability to seal properly. This will allow compression to escape from the cylinder, resulting in low compression.
3. Excessive carbon buildup:
Carbon buildup on the valves and pistons can cause low compression. Carbon build-up will prevent the valves from sealing properly, allowing air to escape from the cylinder during the compression stroke. Additionally, the carbon build-up can cause the piston rings to become “stuck” in their grooves, preventing them from sealing properly.
It is important to use high-quality fuel and keep the engine clean to prevent carbon build-up. Additionally, regular tune-ups will help to remove any existing carbon build-up.
4. Broken Valve Spring:
A broken valve spring can cause low compression in one cylinder. The valve spring is responsible for holding the valves closed during the compression stroke. If the spring is broken, the valves will not be able to seal properly, allowing air to escape from the cylinder.
5. Blown Head Gasket:
A blown head gasket can lead to low engine compression for a few reasons. First, if the head gasket is damaged, it may no longer be able to create a seal between the cylinder head and the engine block. This can allow combustion gases to leak into the cylinder, which reduces the amount of pressure that builds up during the combustion process.
Additionally, a blown head gasket may also allow oil to leak into the cylinders, lubricating the piston and rings and preventing them from sealing properly. As a result, the engine will not be able to build up enough pressure to compress the air/fuel mixture.
6. Flat camshaft:
A flat camshaft can also lead to low engine compression. The camshaft is responsible for opening and closing the valves during the intake and exhaust strokes. If the camshaft is damaged, it may not be able to open the valves properly, which will prevent air from entering the cylinder during the intake stroke. This will result in less air being available for the combustion process, which will lead to low compression.
Additionally, a flat camshaft may also prevent the valves from closing properly during the compression stroke. This will allow air to escape from the cylinder, resulting in low compression.
7. Bent pushrods:
Pushrods are an integral part of the engine, transferring the force from the camshaft to the valves. Without pushrods, the engine would not be able to function.
Pushrods are connected to the camshaft at one end and the valves at the other. As the camshaft rotates, it lifts the pushrod, opening the valve. When the valve is open, air/fuel mixture can enter the cylinder. Once the pushrod has opened the valve, it returns to its original position and closes the valve. This process repeats itself repeatedly, providing power to the engine.
Bent pushrods can cause low engine compression for a few reasons. First, they can prevent the valves from closing all the way, which obviously reduces compression. Second, bent pushrods can also throw off the engine’s timing, leading to reduced power and efficiency. Finally, bent pushrods can cause vibration and other issues that can damage engine components.
8. Broken Timing Belt or Chain:
The timing belt or chain is responsible for synchronizing the movement of the pistons and valves. If the timing belt or chain breaks, the engine will no longer be able to function properly. The pistons and valves will no longer be in sync, which can cause a host of problems.
One of those problems is low engine compression. When the timing belt or chain breaks, the valves will no longer be in sync with the pistons. As a result, the valves may not close properly during the compression stroke, allowing air to escape from the cylinder. This will lead to low compression and reduced power.
The timing belt or chain is an important part of the engine, and it should be checked regularly for wear and tear. If it breaks, it can cause a lot of damage to the engine.
9. Hole in Piston:
A hole in the piston can also cause low engine compression. The piston is responsible for moving the air/fuel mixture into the cylinder during the intake stroke. If there is a hole in the piston, it will allow air to escape from the cylinder during the compression stroke. This will obviously lead to low compression and reduced power.
Wear and tear is the most common cause of holes in pistons. Over time, the piston will start to wear out and develop weak spots. Eventually, those weak spots will turn into holes.
Overheating can also cause holes in pistons. If the engine overheats, it can cause the piston to expand. This can lead to the piston breaking or developing weak spots that turn into holes.
10. Bad Intake and Exhaust Valve:
The intake and exhaust valves are responsible for letting air in and out of the cylinder. If they are not functioning properly, it can lead to low engine compression.
A few different things can cause the intake and exhaust valves to fail. The most common is simply wear and tear. Over time, the valves will start to wear out and become less effective.
Another common cause of valve failure is carbon buildup. Carbon can build up on the valves, preventing them from opening and closing properly. This will obviously lead to low compression and reduced power.
11. Dropped Valve Seat:
The metal valve seat is the part of the engine that the valves sit in. If the valve seat becomes loose, it can fall out of position and cause low engine compression.
When a valve seat drops, it allows the valves to move around and not seal properly. This can cause the valves to leak and not compress the air properly. In some cases, dropped valve seats can also cause the valves to hit each other and bend. All of these problems lead to decreased engine performance and fuel economy.
12. Cracked Cylinder Head:
A cracked cylinder head can also cause low engine compression. The cylinder head is responsible for sealing the cylinders and keeping the air/fuel mixture in. If it cracks, it can allow air to escape from the cylinders, leading to low compression.
There are a few different things that can cause a cylinder head & cylinder walls to crack. The most common is simply overheating. If the engine gets too hot, it can cause the cylinder head to expand and crack.
A cracked cylinder head can also be caused by a manufacturing defect. In some rare cases, the cylinder head can be defective and crack when it’s installed on the engine.
What are the Symptoms of Low Engine Compression?
The most common symptoms of low engine compression include:
- Loss of Power
- Low Fuel Economy
- Car Won’t Start
Let’s see these symptoms in detail:
One of the most common symptoms of low compression in an engine is misfiring. If your car is misfiring, it means that the air/fuel mixture is not being compressed properly and is not igniting properly.
Misfires can also be caused by other problems such as a dirty air filter, bad spark plugs, or a faulty ignition system. If your car is misfiring, it’s important to have it checked out by a mechanic to diagnose the problem.
2. Loss of Power:
Another symptom of low engine compression is a loss of power. If your car is losing power, it means that the engine is not able to generate enough force to move the car. This can be caused by a number of different problems, but low compression is one of the most common.
3. Low Fuel Economy:
If your car’s fuel economy is low, it could be due to low compression in the engine. When the engine is not able to compress the air/fuel mixture properly, it uses more fuel than it should. This can lead to a decrease in fuel economy.
4. Car Engine Won’t Start:
Low engine compression can cause starting problems for your car. When the engine’s compression is low, it means that there is less pressure in the cylinders, which can make it difficult for the engine to start.
How To Carry Out a Compression Test?
Compression testing is a relatively simple process that can be carried out with a few tools. You will need:
- A compression tester
- A spark plug socket
- A ratchet
- An extension
Here’s how to carry out a compression test:
Step One: Remove all of the spark plugs from the engine. This will allow you to access the cylinders more easily.
Step Two: Insert the compression tester into the first cylinder.
Step Three: Use the ratchet and extension to turn the engine over until the needle on the gauge stops moving. This will give you a reading of the compression in that cylinder.
Step Four: Repeat this process for each of the remaining cylinders.
Step Five: Compare the readings from each cylinder on the compression gauge. If they are all within a few psi of each other, the engine is in good condition. However, if one or more cylinders have significantly lower readings, then there may be a problem with that cylinder.
How To Fix Low Engine Compression?
One of the most common causes of low engine compression is a leaking head gasket. If your head gasket is damaged, it will lower the overall compression of the engine. A blown head gasket is often caused by overheating, so if your engine has been running hot, this may be the problem.
Some temporary engine restoration treatment products are available that can temporarily seal a blown head gasket. These treatments are only a stopgap measure, though, and should be followed by a more permanent repair as soon as possible.
If your engine is low on compression due to a leaking piston ring, you may be able to fix the problem by simply replacing the rings. This is a fairly easy repair that can be done at home with the proper tools.
Other possible causes of low engine compression include damaged valves, bent pushrods, or a cracked cylinder head. Whatever the case, you will need to replace that particular part to fix the leakage.
In some cases, low engine compression can be fixed by simply topping off the oil. If your oil level is low, it can cause the engine to run less efficiently and lower the overall compression. Adding more oil will often fix the problem and restore normal engine operation.
Low engine compression can be caused by a number of different problems, including a blown head gasket, flat camshaft, bent pushrods, broken timing belt or chain, hole in the piston, bad intake and exhaust valve, dropped valve seat, broken exhaust valves, and cracked cylinder head.
Low engine compression can be a serious problem that can lead to decreased performance and fuel economy. If you suspect that your engine has low compression, it’s important to have it checked out by a mechanic as soon as possible. In most cases, low compression can be fixed with a relatively simple repair.
Frequently Asked Questions
Are there any temporary fixes for low compression?
There are a few ways to temporarily improve low compression in an engine. One way is to use higher quality oil. Another way is to add an aftermarket oil additive. These can help to improve the seals and rings in the engine, which can lead to better compression.
Finally, it’s also possible to use a higher octane fuel, which can help to prevent knocking and improve overall engine performance. However, these are only temporary fixes, and it’s important to have the engine professionally checked as soon as possible to identify any underlying issues.
What is the price of a compression tester?
There is no definitive answer to this question, as the price of an engine compression tester can vary depending on several factors, such as the brand, model, and features. However, you can expect to pay anywhere from $30 to $200 for a quality engine compression tester.
What are the consequences of running your car with low compression?
One potential consequence of running your car with low engine compression is decreased fuel economy. When your engine’s compression is low, it means that less of the air/fuel mixture is being ignited in the cylinders, which can lead to incomplete combustion and wasted fuel.
Additionally, low engine compression can also cause your car to run rougher and idling to be more difficult. In severe cases, low engine compression can cause engine failure. If you think that your car might have low engine compression, it’s important to take it to a mechanic as soon as possible for diagnosis and repair.
What will be the cost of an engine overhaul?
The cost of an engine overhaul will vary depending on the type of engine, the extent of the damage, and the labor costs associated with the repair. However, it is typically a very expensive repair that can range from $1,000 to over $3,000. Therefore, it is important to consult with a qualified mechanic or automotive specialist to get an accurate estimate of the repairs before having any work done.
How long can you drive your car with low engine compression?
You can drive your car with low engine compression for a short period of time, say a few hundred miles, but it is not recommended to do so for an extended period of time. Low engine compression can cause your car to stall and may damage your engine. If you must drive with low engine compression, be sure to keep your speed low and avoid hard acceleration.
What is the average lifespan of an engine?
There is no definitive answer to this question as it can vary based on a number of factors, such as the type of engine, how well it is maintained, and the operating conditions it is subject to. However, most engines have a lifespan of around 100,000 hours before they need to be replaced or rebuilt. However, there are certain cases in which engines have had a life of over 1,000,000 miles as well. But, ultimately, it really depends on the individual engine.
What are the misfiring codes for an engine?
There are a few different codes that can indicate an engine misfire, including P0300 to P0312. These codes all indicate that the engine is having difficulty igniting the fuel correctly, which can lead to a loss of power and decreased fuel efficiency. In some cases, an engine misfire can also cause increased emissions.