What Is Engine Block?- Definition, Function, and Uses

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?

The engine block houses all of the major components that make up the bottom end of a motor. The block, which is also known as the cylinder block, 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 a camshaft.

Usually made from an aluminum alloy on modern cars, older vehicles, and trucks it was commonly cast iron. 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 bores, or a special hard plating applied to the bores after machining.

The block was originally just a block of metal holding the cylinder bores, the water-cooling jacket, 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.

Air-cooled motors, like the old VW flat-four, and the original Porsche 911 sports car motor, don’t really have an engine block. Much like a motorcycle motor, the crankshaft spins in engine cases, bolted together. Bolted to these are separate finned cylinder “jugs”, in which the pistons go up and down.

Related: What is Engine Piston?

Engine Block

Components of an Engine Block

The main structure of an engine typically consists of cylinders, coolant passages, oil galleries, crankcase, and cylinder head(s).

1. Cylinder blocks

A cylinder block is a structure that contains the cylinder, plus any cylinder sleeves and coolant passages. In the earliest decades of internal combustion engine development, cylinders were usually cast individually. Cylinder blocks were usually produced individually for each cylinder.

Following that, engines began to combine two or three cylinders into a single-cylinder block, with an engine combining several of these cylinder blocks combined.

In early engines with multiple cylinder banks such as a V6, V8, or flat-6 engine each bank was typically a separate cylinder block (or multiple blocks per bank). Since the 1930s, mass production methods have developed to allow both banks of cylinders to be integrated into the same cylinder block.

Related: What is Internal Combustion Engine?

2. Cylinder liners

Wet liner cylinder blocks use cylinder walls that are entirely removable, which fit into the block by means of special gaskets. They are referred to as “wet liners” because their outer sides come in direct contact with the engine’s coolant. In other words, the liner is the entire wall, rather than being merely a sleeve.

Advantages of wet liners are a lower mass, a reduced space requirement, and that the coolant liquid is heated faster from a cold start, which reduces start-up fuel consumption and provides heating for the car cabin sooner.

Dry liner cylinder blocks use either the block’s material or a discrete liner inserted into the block to form the backbone of the cylinder wall. Additional sleeves are inserted within, which remain “dry” on their outside, surrounded by the block’s material.

For either wet or dry liner designs, the liners (or sleeves) can be replaced, potentially allowing overhaul or rebuild without replacement of the block itself, although that is often not a practical repair option.

3. Cylinders.

These are the spaces where pistons travel. They are large in size and have precisely formed holes to create a seal with the piston. The size and number of cylinders measure the power and size of an engine.

4. Oil Passages or Galleries.

These allow oil to reach the cylinder head and the crankshaft.

5. Deck.

This is the top surface of the block where the head of the cylinder sits.

6. Crankcase.

This houses the crankshaft and is found at the bottom of modern engine blocks. Other components include engine mounts, core plugs, coolant, ancillary mountings, and faults.

Common problems with engine blocks

The engine block is designed to last the lifetime of the car, but sometimes something goes wrong. These are the most common engine block failures:

External engine coolant leak

Puddle of water under the engine? It could be caused by a holed hose or a leak from the water pump. Sometimes it’s more serious and the engine block itself could be cracked because of overheating or freezing.

Internal engine coolant leak

Usually caused by a faulty gasket allowing water to mix with the engine oil, symptoms are a drop in the coolant expansion tank and a creamy mayonnaise under the oil filler cap.

Porous engine block

Caused by contaminants during the manufacturing process, voids in the casting often cause no issues at all. Sometimes, though, they cause secondary issues with gaskets and a sealant has to be used to fill the void before a new gasket can be fitted.

There’s nothing you can do about a porous engine block, because it’ll have been faulty from the day it was moulded. Having said that, any leaks that may arise from a porous block will be minor and if they surface within the manufacturer’s warranty period the engine should be replaced free of charge.

A broken seal is classified as a wear and tear item, so won’t be covered by your car’s warranty. A gasket is a cheap item to repair, but labour – especially for a head gasket – will be costly because it takes a few hours to fix.

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.

#1. 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.

#2. 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.

#3. 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.

#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 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.

How Much Will Engine Block Repair Cost at a Garage?

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.