What Happens When Water Mixes With Oil In A Car Engine?

Engines are designed as finely tuned precision machines. So what happens if you mix water with oil in the engine?

Water Mixes With Oil In A Car 1 1 What Happens When Water Mixes With Oil In A Car Engine?

What happens when water gets into your car’s engine oil?

Engine oil and water don’t mix. Water can cause the oil to lubricate improperly, with can cause serious, long-term damage to the vehicle’s engine. This can include excessive wear, serious corrosion, or otherwise permanent damage to parts like the pistols and the rings that connect metal parts.

We’ve done lots or research and writing about cars, including working at a dealership for several years. We’ll introduce you to some good sources in regard to what happens to your engine when you add water to the oil.

What does oil do?

We are going to start this by discussing why oil is critically important to your engine. Oil has a series of functions in your vehicle’s engine, all of which basically keep it alive.

Friction and Wear Reduction

This is one of the biggest reasons to keep fresh, clean oil in your engine. Your engine is a bunch of moving metal that creates small and big explosions to make your car move forward. 

These explosions require proper timing and metal rods, cylinders, and pistons all moving in sync to give you the acceleration and control you need over your vehicle.

Oil flows into these areas and makes it possible for the metal parts to move smoothly and on time. Without oil, these parts will eventually (and probably rather quickly) develop poor timing and damage themselves while touching other pieces of metal while moving at high speed.

Clean the engine

Debris and junk can get into your engine block, even with proper filters for your air intake, oil filter, and other filters. 

Since your vehicle runs off heat and explosions, it is readily possible for debris, grease, and varnishes to form on surfaces. 

Oil is designed to help break these down and carry them away. This is also why your oil changes color over time, as it is absorbing tiny and some big particles that could otherwise interfere with engine operation.

Cooling the engine

While the motor oil isn’t exactly your coolant, it does the critical job of helping to move and absorb some of the heat caused by many moving parts and the combustion created within the engine.

The oil itself is formulated to only burn at a relatively high temperature.

What does water do to oil?

Given that oil has rather specific purposes in the harsh environment that is your engine, it is well formulated right out of the bottle to do just those things. This means that decades of scientific research have gone into both developing engines that are meant to last a while and provide better gas mileage than they used to – and that manufacturers know what to put in the oil to make it last longer.

Having water in your engine oil isn’t good. Water will dilute the oil and has the potential to make it to runny or too thick. 

A change in thickness, or viscosity, can have very bad consequences when the motor oil is unable to properly lubricate the engine – or clean it.

The engine is also designed to handle oil of a certain viscosity, and having motor oil that is too thick or too thin because of excess water can result in leaks, which are also a bad problem for an engine to have.

What happens to the engine with water in the oil?

A few bad things. Almost immediately, the engine can be damaged by not having the proper lubrication. 

By this we can mean the rods and pistons that work together to produce combustion can be quickly worn out, if not bent and destroyed. 

Second, and longer term, water getting into the engine can result in corrosion to metal parts that the oil itself was designed to protect. Corrosion within your engine is not good, and as the metal parts of the engine are much more likely to malfunction or simply break and leak if corroded.

Running an engine with oil in it will likely result in needing to replace lots of parts, if not just rebuilding the entire engine. Obviously, both of these options are time consuming and expensive.

Water Mixes With Oil In A Car 1 What Happens When Water Mixes With Oil In A Car Engine?

How does water get into the oil?

While the problem is not common, we’ll review a few reasons you might have water in your oil pan.

Flood waters or heavy rain

While your vehicle probably has an oil pan with a cover, it is still possible for water at high enough pressure to sneak into your vehicle’s engine during a flood. 

This isn’t all that uncommon during hurricanes. When larger hurricanes have hit the coasts of Florida, Texas, Louisiana, and Alabama, they have resulted in an influx of insurance claims – and dealerships clamoring to buy vehicles at auction because water isn’t good for cars and can cause oil problems as well as serious frame and brakes issues.

Accidentally pouring some in

People who don’t know much about cars could accidentally pour water into the motor oil container under the hood and dilute the oil this way.

Intentionally pour some in

This might be a difficult “prank” to pull off, but one could find a way to get under the hood of a vehicle (leaving it unlocked doesn’t help) and dump water into the oil. While obviously rather illegal, this prank would be difficult to catch. Lock your doors!

Can rainwater fall in through the hood?

The good news is that the answer is no. If you see a huge rainfall bouncing off your hood, you might feel better knowing that the hood and exterior of the vehicle are designed to repel water and let it fall off to the sides of your vehicle. Unless you have some serious holes in your hood, you are unlikely to have water get anywhere near the oil.

How do I know if there is water in my oil?

The challenge here is knowing. If you accidentally dumped water or coolant into your engine oil compartment, the problem is pretty obvious. If flood water reached up to the area around your engine bay, you’ll definitely want to do at least the following:

Check the oil

Open the hood and remove the dipstick from the oil compartment. Oil should have either a golden clear, or in some cases maybe a bit darker if you are in need of an oil change for other reasons. If your oil looks milky, runny, or excessively thick, you might have water in the oil pan and shouldn’t start the engine. The same goes for your transmission fluid. Check the transmission fluid. If it looks a color besides red, you probably have water in there.


Unfortunately if you do start your vehicle with water in the oil, you’ll start to hear it right away. The simple suggestion here is to turn your vehicle off and prepare to get a tow truck.

What should I do if I have water in the oil?

If there is water in the oil pan, your best option is to change the oil and filter. You should also remove all possible filters from the engine and let the entire vehicle dry in a warm place for a while.

If you don’t know how to change the oil and filter – or pull other filters, we strongly recommend taking the vehicle to a mechanic. Instead of starting your vehicle and potentially flooding the engine with water filled oil, it’ll be more than worth the money and time to just get the vehicle towed.

A mechanic or otherwise service department will have more of the tools and expertise to know when the engine is dry, and how to get any remaining watery oil out.

Generally speaking, if you even suspect that you might have water in the oil -don’t start the car. Have it towed or begin the process of drying the engine out right away.

Note that if your vehicle was in a serious flood, like from a hurricane, the engine isn’t the only part to worry about. You’ll want the vehicle to dry quite a bit before starting so that you don’t fry the electronics in your vehicle. This also assumes that your vehicle wasn’t already started and running when it got wet – if it was running, you might have a different set of challenges.

Does the engine have a way to filter out water?

Nope, the engine has an oil filter and a fuel filter amongst other filters, but these are mostly to keep out small debris. A small piece of nature or dirt can cause clogs and other problems in the rather small hoses and tubes that carry fuel and oil around. So yes, while you do have filters, they are more likely to be a sign that you have water issue than be able to help you at all.

How does oil get from the oil pan to the engine?

If you look under the hood of your vehicle, you’ll realize that the oil pan is most often mounted under the engine. So how does it defy gravity? The oil pump brings oil from the pan to the engine when needed. 

The oil pump can also be affected by water, but not in the same way. You are more likely to see a dashboard light and potentially the inability to start your engine if the oil pump is fried by water or plain wear and tear.

That’s to say that you can’t readily ‘check’ to see if your oil pump has water, as its an electronic component and might just need drying like the rest of the engine.

How do I prevent water from getting into the oil?

First, and you probably know this, but don’t put water in your oil. In some small engines, you have to mix oil and gas before starting the engine, but this definitely doesn’t apply to cars.

The best way to prevent water from getting into your car is to get your vehicle to higher ground, or even put it on a ramp or blocks.

We know this is might easier said than done, especially if you don’t even know how much water is coming or have a place to work, but it gives you a better chance at preventing serious water damage to your vehicle.

You might have seen photos from recent hurriances where drivers put the vehicle on the highest part of their yard (if they have a yard) on a ramp to put the vehicle several feet above potential flood waters.

Driving your vehicle through standing water also isn’t a great idea unless you have a lift truck or know exactly how deep the water is.

This presents not only a hazard for your vehicle – if the water current is strong enough to reach up to your car, it might also be able to drag you away if you try to get out. We don’t recommend driving through more than a few inches of water. Water on a street can be much deeper than you expect.

Otherwise, we can honestly say that water is simply a rather powerful force of nature. You might not be able to stop it completely, but you have a chance to “fix” it by letting the vehicle dry first.

When it comes to vehicle security and getting pranked with water in your oil, it helps to simply lock your car when you aren’t around to prevent someone from being able to open the hood. Many vehicles now come with a gas tank and hood release so that people can’t pour sugar or anything else into your gas tank, too.

How much water is too much water in the oil?

There isn’t a specific measurement for this. We certainly wouldn’t suggest just adding water to your oil to test it.

If you experience a bad enough flood that it reaches the oil pan, you should consider the entire oil pan compromised and proceed to both change the oil and dry out the entire vehicle.

Key Takeaways

  • Water mixed with oil in your engine is not good, and has serious potential to cause permanent engine damage
  • Oil is meant to lubricate and clean. Water ruins this ability
  • Test for oil in the engine by checking the oil dipstick and transmission dipstick for milky fluids or a change of color
  • Have the oil changed if there is any water in there
  • Don’t start the vehicle if you suspect there is water in the oil or transmission

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