A cracked engine block is a serious problem that cannot be repaired permanently and indicates the need for replacement of the short block (the lower half of the motor) or the car itself (depending on the vehicle's age and value versus the cost of parts and labor). Although rare, cracks do occur and with few--if any--definitive signs. Apart from the appearance of a large, external hole, only inspection and/or disassembly by a qualified expert can determine with certainty whether your vehicle's block is indeed cracked.
Inspect the radiator and overflow reservoir. Radiator fluid is typically clear or bright green. Brown, murky radiator fluid or the presence of motor oil in the radiator and/or overflow reservoir can indicate an internal engine crack.2
Check the oil. Oil on the dipstick should range in color from burnt gold to dark brown. If it's gray in color or if water is present, the block may be cracked.3
Examine the engine block for leaks. A rust or coolant-colored stripe on the engine and/or steam coming from the block can be signs of a crack.