Can Rain Damage Your Car Engine?


Heavy rains are forecast, and the meteorologist warns drivers once again to avoid standing water on the roadway. But how dangerous can standing water be to a car? Sure, it might stall, but can rain damage your car engine?

Rain can damage your car’s engine if you drive through standing water. Modern engines are water-resistant, meaning they are built to make it difficult for water to get in. However, if water gets into the air intake, the engine can suffer significant and expensive damage. 

Driving through a rainstorm, taking it to the carwash, or even leaving the hood up won’t damage your car. However, a flooded engine can be ruined in no time. Read on to find out why you should avoid driving through standing water.

What Happens to a Car Engine if Water Gets In?

What happens to a car engine if water gets in depends on how much rainwater enters the engine. A car’s breather system can evaporate a small amount of liquid, but a significant amount can enter through the air intake or the ventilation system. These can cause the engine to hydrolock.

What is hydrolock? It is shorthand for a hydrostatic lock. Hydrostatic lock happens when water enters an engine’s cylinders in large quantities such that the pistons cannot complete their stroke.    

Under normal conditions, pistons compress air and fuel vapor to complete a cycle. However, they lack the power to compress water. Therefore, the first piston that is flooded stops abruptly, and the others quickly follow. At that point, the engine stops, leaving the driver stranded.

When your mechanic says your vehicle is locked up, they mean you have hydrolocked the engine.

Types of Hydrolock Damage

When water seeps into your engine cylinders at low RPMs, such as idle, your engine might suffer minor, repairable damage. If you are lucky, you might have a stalled engine that you can start once the water evaporates. Alternatively, you might have to have it towed to a shop where a mechanic can look at it. Worst case, you might need hydrolock repair.

As we have seen, if your car gets flooded, the engine can also hydrolock. The engine’s cylinders become flooded, and the car won’t start. In this situation, your engine needs to be drained. You should do this ASAP to keep corrosion at bay. That said, the engine might still be salvageable.   

If your engine is not idling, then a hydrolock can cause severe damage to the engine.

  • The pistons can bend the connecting rods 
  • The crankshaft can get damaged
  • The cylinder walls can fracture 
  • The pressure can blow the oil seals in the cylinder head 
  •  A connecting rod can punch a hole in the engine block – worst-case situation

This level of damage is difficult to repair. Besides, the repairs can cost you thousands of dollars.  Mechanics often opine that replacing a damaged engine costs less than repairing it.

Engine damage can also occur in three key components.  

Crankcase Ventilation System

The crankcase ventilation system is responsible for getting rid of unwanted gasses from an engine’s crankcase. Once the gasses accumulate, the only way to eliminate them is to vent them. However, if water blocks the vents, the gasses cannot be vented. So, water needs to be kept away from the ventilation system.  

Electrical Components

Besides the obvious electronic components found in vehicles, modern cars contain numerous computers to manage systems like the automatic braking system. The electrical system in modern vehicles is more water-resistant, but there’s also a risk that these components can get damaged by rain water.

Air Intake

Most car engine damage from flooding occurs when excessive water finds its way into the air intake. When this happens, water coming through the air intake blocks air release, causing the pistons to freeze and the engine to stall. This can lead to a hydrostatic lock (hydrolocking). 

What Should I Do if a Car Stalls in Water?

If your car stalls in water, the most important thing to do is stay calm. Your car might not be damaged beyond repair. So take stock of your situation and then decide on the best way to keep you safe such as killing the engine or reversing and backing out.

  • Shut off the engine. When your car is stranded in standing water, this is the best option. Kill the engine and call for a tow truck. The sooner you turn off your vehicle, the greater the chance you won’t damage the engine.
  • Reverse and back out. A foot of rushing water can push your car off the road. Thus, if you’re sitting in a strong current, don’t focus on potential engine damage. Instead, try to back out of the water slowly.

As soon as you get your vehicle to a safe spot, stop the engine to avoid further damage. Also, keep in mind that in the majority of cases, speeding through standing water will spray more water into the engine than driving slowly

How To Check for Damage 

To estimate whether the engine got damaged, check the watermark — the dirty water line on the side of your car. If water didn’t rise past the door’s bottom, the engine would probably have suffered  minimal damage or none.  

However, the closer water gets to the hood, the more likely that your engine has suffered significant damage, including water getting inside the engine. An insurance adjuster will typically total a car that has been submerged.  

If your car has been flooded, check out this video for some Life Hacks on how to save it:

Why Doesn’t a Carwash Damage a Car’s Engine?

A carwash doesn’t damage a car’s engine because the engine is water-resistant. This provides the lowest level of protection against water intrusion. Even though water may come into contact with the engine, it is rare for the engine to get damaged. 

That said, a car engine is not water-resistant. Let me expound on this.

  • Waterproof: A waterproofed item can be completely immersed in water. Few consumer items are entirely waterproof. Often, manufacturers will use waterproof and water-repellent as though they mean the same thing.  
  • Water-repellent: Water-repellent products are designed to keep water from penetrating an object. They do so by slowing down the rate at which water can penetrate. Cell phone manufacturers who describe their phones as water-repellent place time and distance qualifiers on their claims.
  • Water-resistant: This is the lowest level of protection. A water-resistant product is constructed to make water infiltration more difficult.  

Car engines are water-resistant, not waterproof. They can resist the water from a carwash. Indeed, engines are subjected to moisture from humidity that they burn off quickly. Some car owners periodically wash the car’s engine, ensuring they keep water away from areas like the air intake.

Bottom Line

Car engines are designed to handle everyday amounts of water, such as when water or snow gets sprayed into the engine well. However, car engines are not waterproof, and if water gets into the air intake, there’s a chance that the engine will hydrolock. To avoid the risk, do not drive through standing water during a storm. 

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