A cracked engine block is a rare, but potentially serious, engine problem that can occur for a variety of reasons. Responsible for enveloping and securing the main combustion centres of an engine, an engine block is made to be highly durable and heat/cold resistant. However, engine blocks can, and do, develop cracks. There are some obvious signs of a cracked engine block.
Oil in Antifreeze
Engine antifreeze that has oil mixed in it is a classic sign of a cracked engine block and/or a blown head gasket, both of which can allow circulating engine antifreeze to mix with circulating engine oil. The engine block contains the small passageways through which oil and antifreeze circulate throughout a vehicle's engine. If an engine block crack develops in close proximity to these passageways, circulating engine oil can mix with, and pollute, circulating engine antifreeze. This condition can normally be verified when the engine radiator cap is removed and the condition of the engine antifreeze is inspected.
Antifreeze in Oil
Just as a cracked engine block can allow engine oil to mix with circulating antifreeze, the opposite can scenario can also occur: antifreeze can mix with circulating engine oil. This type of a situation only happens when an engine block has a severe enough or deep enough crack that allows the antifreeze to enter the engine oil passageways. Normally, antifreeze-contaminated oil produces a funny smell and/or visible smoke emanating from a vehicle's exhaust pipe, or cloudy, milky-coloured oil that can be visually spotted on the engine dipstick during a routine oil inspection.
Low Engine Compression
Engine compression, which is the end result of engine combustion, is housed within the engine cylinders, which are located within the main engine block. A cracked engine block can result in low engine compression if the crack is severe enough and/or deep enough within the engine block to pierce any one of the engine cylinders. At this point, normal engine combustion pressure is disrupted, which in turn, lowers engine compression and results in poor engine performance.
Engine smoke is often times seen in vehicles with cracked engine blocks. Smoke emanating from within an engine is normally caused by a severely cracked engine block; a crack severe enough to allow engine combustion and engine exhaust gases, which normally present as black and/or bluish grey coloured smoke, to flow directly out of the cracked portion of the engine block. These types of severe engine block fractures normally create severe engine performance problems, in addition to visible smoke.
Visual Crack in Block
Many times, a routine vehicle engine inspection will uncover a cracked engine block. If an engine is clean enough and free from excess dirt and/or grime, a visual engine inspection, which is often times performed during a routine engine tune-up or engine service, can spot engine block cracks that are severe enough to cause significant fracturing of the engine block casing material. Normally, large engine block cracks cause obvious engine mechanical symptoms, but in rare cases where no engine mechanical symptoms are produced, large engine block cracks can be spotted visually during routine engine maintenance.
Engine overheating can occur if a cracked engine block is severe enough to allow engine antifreeze to leak out of the engine, which causes engine temperatures to rise, and the engine to overheat. Engine antifreeze circulates deep within an engine block, in and around the main engine combustion chambers. Therefore, only severe engine block cracks, cracks that extend deep enough inside of an engine to expose the passageways through which antifreeze circulates, would cause engine overheating.