When your car exhibits a rise in engine temperature as made evident by the temperature gauge in the console, a radiator test should be performed. External coolant leaks are relatively easy to spot with no special tools required, but internal leaks are a different story altogether. An overheating engine could be caused by many factors such as low coolant level due to leaks, faulty thermostat or a blown head gasket.
Check the engine bay for any leaks that may resemble the color of your engine coolant. Most leaks stem from cracked radiator hoses due to old age or faulty installation. Replace the hoses when necessary. Remember that a hot engine will produce an extremely hot coolant in the radiator. Take precaution when checking hoses, especially in a hot engine.
White smoke emitted from the tailpipe, brownish coolant in the reservoir, a change in color of the engine oil or a rise in level of oil could mean a head gasket failure or a faulty engine cooling system. This can be diagnosed by a radiator test or coolant pressure test.
A cooling system pressure tester is used to perform this test and is installed in place of the radiator cap. Take precaution when removing the radiator cap on a hot engine, because the pressure buildup could cause serious burns and scalds. Never remove the radiator cap when the engine is hot.
Another way to pressure test the radiator is performed by doing the following:
In extreme cases the cylinder might be filled with coolant and water. This situation is known as hydro lock or hydraulic lock, and could cause serious engine damage when left untreated. If this is the case, try to remove the spark plugs and check for accumulation of water in the cylinders. Removing the spark plugs will allow the accumulated mixture of water and coolant to escape through the spark plug holes.
A qualified mechanic should be consulted once a loss in pressure is observed in the radiator. A faulty head gasket will not only cause hydraulic lock but will corrode the various metal parts inside the engine, leading to more expensive repair bills.