Engine Block: Function, And Symptoms of a Cracked Engine Block

What is an Engine Block?

In an internal combustion engine, the engine block is the structure which contains the cylinder, cylinder sleeves, coolant passages, and other components.

This is where the crankshaft spins, and the pistons move up and down in the cylinder bores, fired by the fuel combusting. On some engine designs, it also holds the camshaft.

In an early automotive engine, the engine block consisted of just the cylinder block, to which a separate crankcase was attached. Modern engine blocks typically have the crankcase integrated with the cylinder block as a single component. Engine blocks often also include elements such as coolant passages and oil galleries.

A typical engine block unit is made up of a number of cylinders, depending on the type and specification of the engine model being built, and it will include cylinder walls, coolant passages, and cylinder sleeves.

engine block


As a central element of an internal combustion engine, alongside the cylinders, the engine block brings together the crankshaft bearing, and for water-cooled engines, the cooling jacket. The auxiliary units needed for the operation of the engine are also generally attached to the engine block.

The purpose of the engine block is to support the components of the engine. Additionally, the engine block transfers heat from friction to the atmosphere and engine coolant.

Materials and design

Engine blocks are normally made from one cast part. Materials used usually include cast iron, spheroidal graphite iron, and lightweight metals (predominantly aluminum). For larger engines, the engine block is separated into two or more cast parts. In this case, the crankcase cylinders are most frequently produced separately.

Its metal construction gives it strength and the ability to transmit heat from the combustion processes to the integral cooling system in an efficient manner. Aluminum blocks typically have an iron sleeve pressed into them for the piston bore, or a special hard plating applied to the bore after machining.

The block was originally just a block of metal holding the cylinder bore, the water-cooling jacket, the oil passages, and the crankcase. This water jacket, as it’s sometimes known, is an empty system of passages, circulating coolant in the engine block. The water jacket surrounds the engine’s cylinders, of which there are usually four, six, or eight, and which contain the pistons.

When the cylinder head is in place secured to the top of the engine block, the pistons move up and down within the cylinders and turn the crankshaft, which ultimately drives the wheels. The oil pan sits at the base of the engine block, providing a reservoir of oil for the oil pump to pull from, and supply the oil passages and moving parts.

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Types of Engine Block

The following are the types of engine blocks:

  • V Engine Cylinder
  • Inline engine cylinder block
  • Opposed engine cylinder block.

1. V Engine Cylinder

It is the popular engine cylinder type and is widely used nowadays. In this configuration, the engines are arranged in two rows.

The two rows are set at an angle to each other. The angle V is kept small, usually 15° to 20°, because with a larger angle the balancing of the engine becomes more difficult. This type of engine is rather difficult to balance with counterweights on the crankshaft.

The crankshaft has only two cranks, with connecting rods from opposing cylinders in the two rows being attached to the same crankpin.

Every two connecting rods are attached to a single Crankpin. Different kinds of V engines are, for heavy vehicles V16, V8s, and for small motorcycles V4s is used as the cylinder block.

2. Inline Engine Cylinder

The cylinders of the in-line engine arrange in a single line. The vehicles which have inline engines work very smoothly. Therefore, they are mainly used when high speeds are required.

The automobiles which have such type of engine block run smoothly. Inline engines are employed for passenger cars.

3. Opposed Engine Cylinder/Boxer Engine Cylinder

The Boxer engine is basically a flat-pressed V engine. These cylinder blocks consist of two rows of two cylinders, each facing each other. This design is also known as a pancake engine. This requires very little headroom so the engine compartment can be very compact.

The Volkswagen engines have this type of arrangement of 4 cylinders. It is air-cooled and is mounted at the rear of the car. This boxer engine cylinder is also used on Porsche and Subaru, and some other higher engines.

What Causes A Cracked Engine Block?

While there are a number of problems that can result in a cracked engine block, most involve excess heat, which is usually caused by an issue with coolant. When this occurs, the overheated portions of the engine expand, while the cooler areas do not. This, in turn, can result in the placing of stress on the block, which can then cause a crack in the engine to form.

Water pump failure can also cause cracks to form in an engine block, as the water pump can stop coolant from flowing through the system as intended, which can then cause severe overheating. Alternatively, casting failure during the injection molding process can cause an engine block’s mental to be thinner in certain areas. Once the heat is applied to these areas, thin cracks can form.

Common Signs of a Cracked Engine Block

It is uncommon to have a cracked engine block. The cylinder head(s) usually crack and start causing problems long before the block does. But there are instances where a block can crack, resulting in some of the following symptoms.

1. Smoke from Under the Hood

There are coolant passages that run through the engine block. A crack in the block may cause the leakage of coolant from the passages into one of the engine’s cylinders. The burnt coolant on the engine’s cylinder causes combustion, resulting in the white smoke/steam coming out of the vehicle’s exhaust pipe.

2. Coolant or Oil Leaks

If you notice a small or large puddle under the car and its oil or coolant, then it is not a good sign. An oil leak can most likely happen from an oil filter, drain plug, or anywhere with oil flow, including a channel within the cylinder block. A cracked engine can cause an internal or external coolant leak.

3. Engine Overheating

On your car’s dashboard, there is the engine temperature gauge connected to the coolant temperature sensor. You must keep an eye on it while you’re driving. When an engine block is cracked it results in a coolant leak (either internal or external) and prevents the proper circulation of the coolant through the engine. And as a result, the engine can start to heat.

Under normal circumstances, the needle on the gauge doesn’t show an increase in the temperature until the engine has time to warm up. During summer, this might happen within a couple of minutes while in winter it could take ten minutes of driving to show the rise in the temperature.

Most engines run at between 85 and 100 degrees Celsius. And anything that is considered too hot for the motor will be shown as the red range on the gauge. So, if you see the needle in this area, know that the engine is overheating. Immediately, pull over and switch off the car to allow it to cool.

4. 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.

5. 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.

6. Coolant-Oil Intermix

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

7. Illuminated check engine light

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.

How To Drain Coolant from Engine Block?

Flushing out accumulated dirt and other forms of build-up from the cooling system will help your engine to run more smoothly for longer. For many cars, it may never be necessary to flush the engine block – it’s only vehicles that aren’t driven for an extended period or go a long time without oil changes that might need a full flush out.

The basic steps to flush a car engine block are:

  • Remove the lower radiator hose and catch the draining coolant in a bucket.
  • Remove the top radiator hose and flush the system out with a normal hose.
  • Continue until the water runs clear out of the bottom of the engine.
  • Refill with coolant and reattach the radiator hoses.

The exact process will differ from vehicle to vehicle, so consultation with your vehicle manual will be essential when it comes to performing a flush of the cooling system.

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Cracked Engine Block Repair Cost

A failure in the engine block will leave you stranded and more often than not facing a huge repair bill (at least $1,200, probably more).

The cost of repairing a cracked engine block can vary considerably depending on the garage you visit, the severity of the crack, and the car you drive.

The technique used to repair the crack can also affect the total and you may have to weigh up the sense in repairing it when it may be more cost-effective to buy a new engine or even a new car.