What Causes Hydrolock? A Quick Guide for Students in Auto Mechanic Courses


Water can be a terror for vehicles, unless it’s used as part of window washer liquid or engine coolant. It has the potential to cause destruction to expensive mechanical components, but it’s a substance which is very difficult to avoid. Puddles, and occasionally floods, form on the road surface and auto mechanics know it’s not worth the hassle to go splashing into them.

One of the problems caused by the intrusion of water into the engine compartment is hydrolock. This process causes varying degrees of damage, but at its worst, it can trigger the mechanical and financial pain of a full engine replacement. So let’s take a closer look at the problem, and how it can best be avoided by vehicle owners.

Watch out for Piston Damage when Assessing Hydrolock

Before we get into the causes of hydrolock, let’s first look at what’s involved in this type of mechanical failure. It all revolves around the pistons in the engine, which are an integral part of the combustion process. The pistons move up and down a cylinder, compressing a fuel-air mixture to get the vehicle moving. Water causes serious damage if it enters the cylinder, because it can’t be compressed. This creates tension which can bend and break the piston rods. Eventually the pistons stop on the upstroke, hence they ‘lock’ into place.

Those who studied in a mechanic certification program know that water can attack these pistons by entering the vehicle through the air intake. This is located directly behind the radiator grille, so it is in prime position to collect water if driving in wet conditions.

The Obvious and Rare Causes of Hydrolock to Be Aware of During Auto Mechanic Courses

Suffering water damage is just the first step in causing hydrolock. It is usually the actions taken directly afterwards that determines the scale of the damage. If the vehicle has been flooded while the engine wasn’t running, drivers should be advised to seek repairs without attempting to start the engine. Hydrolock also occurs while the vehicle is moving, however, like when a driver misjudges the depth of water on a particular road. Water may instantly get sucked through the air intake and into the cylinders, bringing the engine and vehicle to a halt.

There are other causes which don’t involve floodwater. A blown head gasket can cause engine coolant to enter the cylinder, while it can also become contaminated with liquid fuel if the injectors or carburetor are ineffective.

Keep the Engine Healthy with These Preventative and Repair Measures

Graduates of auto mechanic courses know that water damage is often unavoidable, but there are preventative measures which should be followed to ensure no long-term damage occurs. The cylinders must be given an opening through which to expel water, and this is done by removing the spark plugs from the engine. When the vehicle is started, the water is blown out of the openings. Further repairs will be needed, however, if leaking coolant is the root cause of the damage.

If the pistons have already been damaged because of hydrolocking, then the necessary repairs will be more extensive. As well as bent and broken pistons, water damage in the cylinders can crack the crankcase underneath. Repairing or replacing these components can be quite an expensive process, and a full engine replacement is often a more cost-effective option.

Hydrolocking may require a full engine replacement

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