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What is an engine block & what does it do

What is an engine block (and what does it do)

An engine block - also known as a cylinder block - contains all of the major components where the combustion process takes place in a reciprocating engine. 

Usually made from an aluminium alloy (cast iron in older engines), it houses the cylinders and their components, the water cooling system and the crankcase. 

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. 

This water jacket, as it’s sometimes known, is supplied by the car’s radiator, which cools the water before it is pumped back into the engine block. 

Without cooling, the engine quickly becomes less efficient and would ultimately seize.

The water jacket surrounds the engine’s cylinders, of which there are usually four, six or eight and which contain the pistons. 

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.

When the cylinder head is in place (it secures to the engine block), together with the camshaft, 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. This reservoir provides lubrication for the engine’s moving parts and its level is checked electronically, via the car’s dashboard, or with the use of a dipstick, which is installed in the engine block. 

The engine oil should be changed at prescribed intervals - this is done via the sump plus, which sits on the base of the block, or by using a vacuum pump and a hose inserted through the dipstick hole. The oil filter should be changed at the same time.