Signs of a Cracked Engine Block

Signs of a Cracked Engine Block
Dusan Petkovic/Shutterstock

The typical engine has more than 200 parts subject to the wear and tear of life on the open road. You may be familiar with failure points on common engine parts, such as the starter, head gasket or intake manifold. But a cracked engine block could also be the culprit for some engine issues you may experience.

A cracked engine block is not a common problem. But being armed with this knowledge can help you eliminate or diagnose the issue.

What is an engine block?

An engine block houses all of the combustion activities of a modern car engine. It also provides passage for cooling and lubrication fluids.

During normal operation, pistons move up and down thousands of times a minute as the crankshaft spins. All of this mechanical intricacy must be properly cooled and lubricated. All of this happens in the engine block.

This durable component is typically constructed of a metal alloy and built to withstand the heat cycles that occur within a modern engine.

Cracked engine block symptoms

The engine block is the foundation of a vehicle’s engine. Once the block is compromised with a crack, fluids no longer remain where they should be. The internal combustion process is no longer contained within the cylinders.

Once you have a cracked engine block, you’re likely to see one, a few or even all of these symptoms.

Visible crack in the block

Upon inspection of your engine, you may notice a visible crack. Sometimes this does not reveal any other mechanical problems. You may not see any fluid leaks, either. However, it’s usually only a matter of time before the crack spreads and causes serious engine problems.

Poor engine performance

In order to create power, an engine uses a series of small explosions contained within the cylinders of an engine. Containing this energy is known as compression, which allows an engine to produce power.

A cracked engine block can cause a loss of compression in one or more cylinders. Drivers will notice an immediate reduction in engine performance because one or more cylinders are not functioning. This is, in effect, like running on three out of four cylinders if you drive a four-cylinder car.

Depending on the severity and location of the crack, this condition can render your vehicle inoperable. A mechanic will run a compression test to determine if this is an issue.

Engine overheating

Engines with a cracked block frequently overheat because they lose coolant. Because there are channels within the block that contain engine coolant, any crack within the block can cause a leak.

White or blue smoke

If you have a crack in your engine block, and the crack is between cylinders, you can have a variety of smoke colors coming out of your exhaust pipe. Typically, if coolant is leaking into your combustion chambers, the smoke will be white. If oil is leaking into your combustion chambers, the smoke will be blue.

If you have an exposed external crack weeping coolant or oil, smoke may also come out from under your hood.

Rough idle

An engine is balanced to provide a shake-free ride both while underway and at rest. Once a vehicle loses compression in a cylinder, a vehicle with a cracked engine block will often experience a rough idle. A rough idle can be felt in the passenger compartment and will register on the tachometer as well.

Typically, the computer on modern engines tries to accommodate for the lack of compression by varying the engine speed in an attempt to maintain balance. But this is seldom successful and very noticeable.

Oil in antifreeze

If you have a cracked engine block allowing engine oil into the cooling channels, you will notice a milkshake-like substance in your vehicle’s radiator or overflow tank. This is a direct result of oil and antifreeze mixing.

There are other conditions that can cause oil to get into the antifreeze, such as a blown head gasket, but if you see oil in the antifreeze along with other conditions noted here, you may have a cracked engine block.

Antifreeze in oil

Depending on the location of the crack, you may check your oil between changes and notice a milkshake-like substance on your dipstick. Much like getting oil into antifreeze, antifreeze that leaks into oil will also cause a milkshake appearance.

Antifreeze is not up to the task of lubricating engines. It can cause major engine damage just by being present where the engine oil should be. Again, if you notice a milkshake-like substance in your oil, you have a major problem.

Low coolant levels

If you regularly maintain your fluid levels in your engine and you notice your coolant level dips below the recommended level, a cracked engine block may be weeping antifreeze out of your engine.

Sometimes cracks can be so small the coolant evaporates before hitting the ground underneath your vehicle, making the problem elusive to track down and repair. Coolant level loss of a quarter-inch every three months is considered normal, especially on older engines. Anything more than that could be cause for alarm.

What causes a cracked engine block?

A cracked engine block can be caused by multiple factors, including everything from poor maintenance to manufacturing defects. Because an engine block is designed to be durable, the conditions that cause the crack tend to be quite extreme.

Poor maintenance and overheating

One of the main causes of a cracked engine block is poor vehicle maintenance.

A well-maintained vehicle will remain lubricated and cooled under a variety of driving conditions. Infrequent oil changes, improper cooling system maintenance and general neglect can cause an engine to overheat. Once extreme heat is applied to metal, the metal can expand and crack.

Extreme cold weather

In extreme cold weather conditions, a vehicle’s engine coolant can freeze. Coolant is designed to stay liquid at freezing temperatures—that’s why it’s also known as antifreeze. But those capabilities have limits, especially if the coolant is not rated for extreme temperatures. If the coolant freezes, the expansion of the frozen material inside the engine can cause a crack.

In addition, extreme cold temperatures can negatively affect many types of engine alloys, causing them to become more brittle and prone to cracking.

Performance upgrades

If you’re an enthusiast, you may consider upgrading your engine with forced induction. These components, known as turbochargers and superchargers, are designed to force-feed incredibly dense air into an engine’s combustion chamber. This condensed air mixes with gasoline and is ignited by the spark plug, producing a larger and more violent explosion than a standard engine.

An engine designed from the outset with a turbocharger or supercharger is built to handle the forces of forced induction. However, adding one of these devices to an engine not designed for it can cause the engine block to crack because of the added stress.

Manufacturing defects

Although rare, manufacturing defects can cause an engine block to crack without any other conditions present. This is typically because of an alloy not properly treated to withstand heat or other flaws in the engine manufacturing or casting process. Recently, the eighth generation Honda Civic was subject to investigation and subsequent lawsuits for this exact problem. Running a vehicle recall check may reveal if this is a problem for your vehicle.

Can you repair a cracked engine block?

The short answer is yes. The real question is whether you’re capable of performing this complicated repair on your own.

Repairing a cracked engine block entails stripping the engine of all its attached components and often means disassembling parts of the engine to get to the crack. Once your engine is disassembled, you need to repair the crack. There are commercial sealants available from companies like Belzona or Blue Devil. Otherwise you have to weld the crack.

Unless you’re an accomplished mechanic, this is a job better left to the professionals.

Cracked engine block repair costs

A cracked engine block is an expensive and time-consuming endeavor. It can cost thousands of dollars and have your car off the road for anywhere from a few days to a few weeks.

If your vehicle has a cracked engine block, your options are to either repair the block, replace the block or replace the entire engine.

Engine block repair

If your mechanic says your engine block can be repaired, this is likely the cheapest option. However, an engine block repair is not always practical or cost effective. It really depends on where the crack is on the block.

2014 Honda Civic Engine Block Repair: $2,800-$3,200

Engine block replacement

Rather than repair the engine block, replacing the entire block is the route many owners and mechanics decide to take. This is less risky than simply repairing the crack. However, most replacement engine blocks are used, not new. There’s no way to tell if the donor block was well-maintained.

2014 Honda Civic Engine Block Replacement: $3,500-$3,700

Engine replacement

Replacing the engine on your vehicle may seem like a worst-case scenario, but this also means you can cover any other potential defects your engine may have as a result of the cracked engine block. For example, if your engine cracked because of overheating, there’s a good chance other components in your engine are also damaged.

2014 Honda Civic Engine Replacement (rebuilt engine, made in Japan): $5,500-$6,000

The used engine often comes with a warranty from the shop and typically arrives already rebuilt from an off-site facility that specializes in this type of work. Although this is the most expensive option, it is the most comprehensive: A new engine can extend the life of your vehicle by several years.

About Bumper

At Bumper, we are on a mission to bring vehicle history reports and ownership up to speed with modern times. A vehicle is one of the most expensive purchases you'll likely make, and you deserve to have access to the same tools and information the pros use to make the right decisions.

About Daniel Russo

Daniel is an automotive writer and motorsports enthusiast based in sunny Southern California. After studying journalism at San Francisco State, he found his passion for connecting some of the best automotive brands with their enthusiast customers. Daniel has been published by Consumer Affairs and has handled communications for the legendary Laguna Seca Raceway for the automotive Mecca of the city of Monterey, CA.

Disclaimer: The above is solely intended for informational purposes and in no way constitutes legal advice or specific recommendations.