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A cracked engine block is bad news—in the world of automotive repair, it’s one of the most serious (and costly) problems you might encounter. Sometimes, the issue is mistaken for a blown head gasket or cracked cylinder head because it can present many of the same symptoms. But unfortunately, a cracked block is far worse than either of those problems, as it usually means your car needs a new engine.

What is an Engine Block?

Your car’s engine block is an aluminum or cast iron casting that acts as the bottom portion of the engine. The block provides a foundation for the cylinder head(s) and other major engine components. Also, the block houses the crankshaft, pistons, connecting rods, and (in some cases) the camshaft.

The block and its internal components are often referred to as the “bottom end” of the engine. Meanwhile, the cylinder head(s) and related parts are considered to be the “top end” of the engine.

cylinder block of truck engine
The engine block provides a foundation for the cylinder head(s) and other major engine components.

Common Signs of a Cracked Engine Block

A cracked engine block is rather uncommon. Usually, the cylinder head(s) crack and start causing problems long before the block does. Still, there are instances where a block can crack, resulting in one or more of the following symptoms.

Note: Because other problems can present the same symptoms as a cracked block, you’ll want to perform a thorough diagnosis of the vehicle before performing any repairs.

White Smoke (Steam) From the Exhaust Pipe

There are coolant passages that run through the engine block. A crack in the block can allow coolant from those passages to leak into one of the engine’s cylinders, where the coolant is then burned during the combustion process.

As a result, you’ll see white smoke, which is actually steam, coming out of the vehicle’s tailpipe. You might also notice that the exhaust fumes have a sweet smell.

Coolant or Oil Leaks

A cracked engine block can result in an internal or external coolant leak. An external engine oil leak is also possible, depending on the location of the crack.

Engine Overheating

A cracked engine block can result in a coolant leak (either internal or external) that prevents the coolant from properly circulating through the engine. The engine can start to overheat as a result.

Rough Running and Misfiring

In some cases, a cracked engine block can result in a loss of compression that causes the engine to run rough and misfire.

Combustion Gases In the Cooling System

A cracked engine block can allow combustion gases to enter the cooling system. As a result, you might see an excessive amount of bubbles in the coolant before it begins to boil. You might also notice that the cooling system is under extreme pressure.

Coolant-Oil Intermix

It’s possible for a crack to develop between the block’s oil and coolant passages, resulting in coolant-oil intermix.

Illuminated Warning Lights

A cracked block can trigger the check engine light, low coolant level light, and the engine over-temperature light. If your car is equipped with a temperature gauge, you’ll also see it begin to climb.

Engine Block FAQ

What Causes a Cracked Engine Block?

Engine overheating is the most common cause of a cracked block. When the engine gets too hot, the block can crack as a result of thermal stress.

Also, the block can crack in freezing temperatures if the cooling system is filled with too much water and not enough antifreeze. As the water freezes and expands, it causes the block to crack.

Casting and design flaws can lead to a cracked engine block, as well. For example, eighth-generation Honda Civics (model years 2006-2009) are known for having a casting flaw that eventually causes the block to crack. Honda issued an extended warranty to address the issue.

How to Diagnose a Cracked Engine Block (Common Test Methods)

man use the wrench to remove a spark plugs from car engine
Which test method you choose will depend on whether you’re checking the block for an internal or external crack.

There are various ways you (or your mechanic) can check for a cracked engine block. Which test method you choose will depend on whether you’re checking the block for an internal or external crack. The most common diagnostic procedures include the following:

Visual Inspection

In some cases, you can spot a crack that’s leaking oil or coolant externally by performing a simple visual inspection of the block.

Cooling System Pressure Test

Usually, a block with an external coolant leak can be diagnosed by performing a cooling system pressure test. The method involves pressurizing the cooling system (with a dedicated pressure tester) to pinpoint the source of the coolant leak.

The video below demonstrates cooling system pressure testing:

A cooling system pressure tester can also be used (along with a borescope) to check for internal coolant leaks. The process involves first removing the spark plug from the suspect cylinder, then inserting the borescope into the spark plug hole. Finally, the cooling system is pressurized, and the borescope is used to check for coolant leaking into the cylinder.

Coolant leaking into the cylinder can point to a faulty head gasket, a cracked cylinder head, or a cracked engine block. The engine will need to be disassembled to determine the root cause of the problem.

Once the engine is apart, a machine shop can check the block for cracks using fluorescent dye and/or magnetic crack detection equipment.

Block Tester

A block tester—a device that contains fluid that changes color in the presence of combustion gases—can be used to detect a block that’s cracked internally. The tester is placed over the cooling system filler neck to check for the presence of combustion gases in the cooling system.

If combustion gases are present, the engine is suffering from a leaking head gasket, cracked cylinder head, or cracked engine block. The engine will need to be disassembled to determine the root cause of the problem.

The video below demonstrates using a block tester:

Can You Fix a Cracked Engine Block?

In the past, auto repair shops would occasionally fix a cracked cast-iron block via welding, gluing, or pinning. But these days, most professionals will opt to replace the block (or the entire engine) instead of repairing it.

How Much is a New Engine Block?

Replacing an engine block (or the entire engine) is a costly and labor-intensive repair. If you choose to have a professional do the job, you can usually expect to pay somewhere between $4,000 and $8,000. Of course, the exact cost will depend on various factors, such as the year, make, and model of your vehicle.

Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic.

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