How does an engine water hammer happen?

Why a many-kilometer detour of a flooded road is preferable to driving along it and how to avoid costly repairs after a car encounters a water barrier.

Heavy rains this summer in Moscow, the Krasnodar Territory , in Yakutia and in the Crimea brought a lot of problems to thousands of motorists. The owners of the cars that went under water “got” on expensive repairs. And those who were bypassed by the floods faced the risk of engine water hammer and its consequences. We will deal with the signs and causes of this phenomenon, and also find out how to avoid engine water hammer.

What is a car engine water hammer

Water hammer or water hammer is commonly called a pressure jump in any liquid-filled closed system. When we talk about it in relation to water, which, as is known from the school physics course, is considered incompressible or almost incompressible, this phenomenon can also be accompanied by the destruction of the system components, and also lead to its depressurization.

In a car engine, water hammer occurs in the cylinders and combustion chambers. Structurally, they are isolated from moisture. But when a large amount of water suddenly enters a running motor, a pressure surge occurs and an abrupt stop of the power unit with a characteristic shock, in which the parts experience huge loads and can fail. In the common people, they say about the water hammer “the engine took a sip of water.”

How does an engine water hammer happen?

Water can get into a running engine not only when overcoming streams, rivers and fords, but even when quickly driving through deep puddles or sections of roads flooded after heavy rains . It is sucked into the combustion chamber of the engine through a low-lying air intake. As a result, the pistons moving in the cylinders encounter an obstacle that prevents their normal operation.

When the cylinders try to compress incompressible water, the engine stops abruptly, during which its parts can be deformed or destroyed. During a water hammer, the car will shake violently, after which the engine will stall. For cars with a diesel engine, this phenomenon is even more detrimental, since the compression ratio and compression in such power units are higher than in gasoline ones. Therefore, higher pressure and loads destroy the motor faster and more strongly.

Consequences of a water hammer

The result of a meeting of a car with a  water barrier on the road can be both deplorable and insignificant, if you’re lucky. It depends on a number of factors. For example, on the amount of water that got into the motor. The higher the speed, the more moisture will be in the cylinders. And the higher the engine speed, the greater the load it will experience during water hammer.

Most often, during a water hammer, the following are deformed or destroyed:

  • crankshaft bearings,
  • crankshaft,
  • piston rings,
  • crank mechanisms,
  • camshafts,
  • timing chain or belt
  • cylinder head.

However, if the car that drove into the puddle simply stalled and the driver and passengers did not feel any impact, everything will probably work out. Sometimes electronics suffer from water, preventing the engine from starting. For example, the crankshaft position sensor. When it dries, the car can drive again. To find out if there was a water hammer, check the condition of the air filter. If it is wet, and there is no water in the case, then perhaps not everything is so scary.

What to do with water hammer

If, while driving through a  ford or a deep puddle , the car suddenly stalled and stopped abruptly, do not start the engine again. So you will only hurt him. Turn off the ignition and, in accordance with the traffic rules, indicate to other road users a possible breakdown of your car. After that, open the hood to inspect the power unit and find out if there was a water hammer. First of all, evaluate the condition of the air filter. If wet, remove it.


Inspect the engine for damage and fresh fluid leaks. If nothing is found, remove all spark plugs to make sure there are no drops of water on them. Finding nothing critical, “spin” the engine with the starter candles removed . If there are no extraneous knocks and rattles, put the spark plugs in place and slowly roll into the service on your own. Otherwise, go there, but already on a tow truck.

How to avoid engine water hammer

In order not to have to repair or completely change the engine after a water hammer, follow a few recommendations, the main of which is not to get into this unpleasant situation . Why should you avoid driving through fords or roads with dangerous flooding in a car with a low air intake. It is better to take a detour than to find out the cost of repairing a motor that has taken a sip of water.

Source: Moscow City News Agency

If there are no other options, move slowly through deep puddles, mindful of the location and height of the air intake above the road. Slow down in advance, even before contact with water. And pick up speed already when leaving the puddle. Pay attention to how and where other drivers pass – along the edges or in the center. Follow the path with the least depth.

In the case when the depth of the puddle is not critical, move along it with the rest of the cars. But do it smoothly and evenly so as not to overtake a water shaft launched in front of the bumper, which can overwhelm the hood and flood the engine. For the same purpose, keep your distance from cars in front and beware of waves from waves from oncoming cars. If you can’t part with them, it may be worth crossing the ford in turn.


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