Michael Fernie profile picture Michael Fernie 5 months ago 34
Blog

How Can Hydrolocking Occur, And Why Is It A Potential Engine Killer?

What we're about to tell you may make you think twice about driving fast through deep puddles

Remind me later
How Can Hydrolocking Occur, And Why Is It A Potential Engine Killer? - Blog

Anyone with a grasp on how an internal combustion engine works will know that fire, metal and water do not play well together. Turning your car into a steam engine can only ever lead to two things - a catastrophically large garage bill or a phone call to the local scrapyard to tow your pride and joy away.

Mostly caused by people attempting to drive through large puddles in the road or by unknowingly putting a car at risk through a cold air intake system, hydrolocking can be a firm nail in the coffin for any car. To help you avoid such a cataclysmic event, let’s take a look at the true causes and possible results of this traumatic ordeal.

How Can Hydrolocking Occur, And Why Is It A Potential Engine Killer? - Blog

Hydrolocking is when an engine either seizes or suffers catastrophic failure due to the ingress of a substantial volume of water in the cylinders. With an internal combustion engine effectively resembling a form of air pump, the internals are all designed to deal with the compression of air. Water on the other hand is virtually incompressible unless a huge amount of pressure is applied to it and even then it barely budges.

If water fills the combustion chamber, the rotation of the crankshaft will force the pistons upwards to try and compress the fluid. With the reaction force from the water being larger than the maximum stress the engine components can cope with, something has to give. If the engine is of small capacity and therefore doesn’t generate much force during reciprocation, the motor may simply seize up, grinding to a halt. This can also be the case if hydrolock occurs when an engine is simply idling rather than rotating at any great speed.

This is the least-damaging result, with the engine needing flushed by removing the spark plugs and turning it over to spit the water out. The engine should be fully checked, removing the inlet manifold and cylinder head to check for any further damage and to rid the powertrain of any residing water. Changing any gaskets that could have possibly been affected would also be a wise call.

Your favourite YouTube mechanic is here to spread his wisdom once again

The real damage occurs when a large volume of water makes its way into the cylinders, especially of a powerful engine with a decent capacity that is running at speed. The reaction forces involved will almost certainly break internal components, with the most common failure being the connecting rods.

The connecting rods can bend resulting in the need for replacement and an engine rebuild. Or they can fully snap, causing large shards of metal to bounce around the cylinders and down into the crankcase. Sadly, all this energy has to go somewhere. This can lead to literal holes being blown either upwards through the cylinder head or downwards through the sump. In those cases, the car will require an engine replacement, and that’s only if the owner feels the hassle is justifiable over scrappage.

Some warped connecting rods bent by hydrolocking. Image via 996 Revolution
Some warped connecting rods bent by hydrolocking. Image via 996 Revolution

The most common cause of hydrolocking is simply driving through high water. Many cars have the start of their intake systems near a wheel arch which will often have vents to eradicate large volumes of water. Driving through a large body of water can lead to the water surging up the intake, saturating the air filter and leading to the water entering the inlet manifold. Each revolution of the engine will have water cramming itself into each cylinder until the pistons cannot compress upwards any longer.

Leading on from this, the second cause of hydrolocking is through modifications that place the beginning of the intake system in a compromising position. Seeking a suitable area for a cold air intake, some petrolheads decide to place a cone air filter low in the corner of the bumper. This means it is in the line of fire when driving through any body of water that is only bumper height.

The guys from Mighty Car Mods messing around with cold air intakes
The guys from Mighty Car Mods messing around with cold air intakes

Head gasket failure can also lead to hydrolocking, with coolant entering the pistons rather than keeping to the coolant chambers that course around the engine block to eradicate heat. Head gaskets generally fail due to thermal expansion that is too quick for the gasket to deal with, forcing it to crack or split. Although there are different levels of failure leading to different outcomes, hydrolocking would occur when a severe failure has occurred at a point where the gasket separates the coolant passages and cylinders.

Another (very rare) cause can be an injector leak. An injector that is stuck open or is cracked can lead to the engine quickly becoming flooded with fuel. If you follow Adam LZ on YouTube, you’ll know that this happened to a drift car of his recently, with the intake manifold, cylinders and intercooler needing to be flushed of fuel.

How Can Hydrolocking Occur, And Why Is It A Potential Engine Killer? - Blog

Have you ever experienced hydrolocking? Can you think of an engine failure worse than water ingestion? Comment with your experiences below!