Why is hydrolock incredibly dangerous for car engines?

During the rainy season, especially in a tropical country like Vietnam, flooding in major streets is not unfamiliar. This poses a potential risk for hydrolock, especially for hatchbacks or sedans with low ground clearance and engines.


Hydrolock is a common phenomenon that occurs when liquid enters the combustion chamber, causing the engine to stall. Since liquid is difficult to compress (unlike the typical air and fuel mixture), the piston in the cylinder cannot push down to complete a cycle, resulting in the engine shutting down.

So what causes hydrolock? The first and most common reason is water entering the engine’s air intake system. Driving on flooded streets poses a significant risk of this phenomenon, especially for vehicles with low air intakes like sedans or hatchbacks. Additionally, water can enter the combustion chamber through a damaged or cracked head gasket, also known as a blown head gasket.

Why is hydrolock extremely dangerous for car engines? 001-rolls-royce-ghost-flooded.jpgDrivers need to be proactive and alert when participating in traffic, preferably avoiding any “swimming” when possible.

The extent of the impact of hydrolock on the engine depends on several factors, such as the operating condition of the engine when water enters. If the driver is running the engine without load (when the vehicle is stationary but the engine is still running), the engine will shut down when hydrolock occurs and is usually unable to restart through normal starting procedures. This is the “gentle” case and least harmful to the vehicle.

Unfortunately, if hydrolock occurs at high engine RPM, the consequences become more severe. Depending on the depth of the water and the positioning of the engine’s air intake, water can enter one or several cylinders. In some cases, if only one cylinder is affected, the vehicle may still be able to run for a short distance because the remaining cylinders provide enough power. However, at high speeds, the engine will typically abruptly shut down.

The consequences in such cases are extremely dangerous. The water prevents the piston from moving along the cylinder but still withstands the thrust force from the camshaft, causing the con rod to bend and damaging the bearings and crankshaft. In severe cases, the engine block may even crack, requiring a complete engine replacement. The cost of repair in these situations is significant, and even if the engine does not need replacing, the latent danger of rusting in the cylinders and engine components always threatens stable operation of the vehicle, not to mention the impact of water on electrical parts.

Therefore, drivers need to be proactive and alert when participating in traffic, preferably avoiding any “swimming” when possible. For current ordinary family vehicles, a water height of 20-25cm is a safe level that can be overcome. In unavoidable situations where water must be crossed, maintain a calm mindset, apply gentle acceleration in first gear, avoid sudden throttle increase, and use the clutch (for manual transmission vehicles).

Try to be vigilant and immediately turn off the engine if any abnormalities are detected, minimizing the amount of water entering the engine. Specifically, do not attempt to start the engine again unless it is certain that all water has been expelled from the combustion chamber by removing spark plugs and fuel injectors. In such “gentle” cases, water leaking out of the cylinders can usually be observed, and then the vehicle can resume normal operation. If uncertain about the condition of the vehicle, it is best to find a way to push the vehicle to a higher and dryer location and call for roadside assistance to handle the situation, avoiding further damage to other engine components caused by water.

quangnguyen (forum.autodaily.vn)