Is Motor Oil Flammable?

by Synthetic Oil | Last Updated: March 7, 2022

Did you ever wonder about the accuracy of those movie scenes where a pool of oil ignites at the drop of a cigarette? This is assuming that motor oil is highly flammable. The good news is that you can breathe a little easier while pouring engine oil into your car because you are going to learn all about the flammability of motor oil and how to handle and store it properly today.

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Is Motor Oil Flammable?

No, according to OSHA, motor oil is not flammable. OSHA has defined a flammable liquid as one that ignites or has a flashpoint below 199.4 degrees F (93 degrees C). Motor oil is not flammable but combustible, and it requires a very high temperature to catch fire. In other words, motor oil has a flashpoint of 300-400 degrees F (150-205 degrees C), depending on the kind of engine oil it is.

Other combustible liquids and substances include diesel fuel, kerosene, phenol, paint thinner, naphthalene (used in mothballs), hydrazine, and formaldehyde.

Why is Motor Oil Not Flammable?

Time for a bit of a chemistry lesson. Flammable liquids, such as gasoline and various alcohols, often have shorter changes of hydrocarbons. These molecules will easily release vapors into the air, and since there are trillions of molecules in a liquid, there is a lot of vapor. Those vapors are what catches fire at a lower temperature.

Motor oil, on the other hand, is a denser substance than gasoline. There are long chains of molecules holding the substance together. Oil actually is a mixture of hydrocarbons, not a specific set like flammable liquids. This means that there is more carbon in a molecular chain in oil than there is with flammable liquids.

Okay, that all sounds very confusing, right? Let’s simplify it: Oil combusts because it needs a higher temperature to weaken the bond between those molecules. When that happens, vapors are released all at once, causing the combustion to occur.

At What Temperature Does Motor Oil Catch Fire?

The brand of motor oil you use determines the flashpoint. Some are higher than others. On average, engine oil ignites around 400 degrees F.

Here is a video of someone testing out the flashpoint of motor oil:

The final conclusion of the video finds that motor oil has a flashpoint of around 419 degrees F (215 degrees C).

However, there is one important thing to note. Unlike flammable liquids that release vapors at room temperature, motor oil does not produce vapors unless heated. This means that it will not catch fire unless it has reached a certain temperature—its flashpoint.

What About Synthetic Motor Oil?

Designed with temperature resistance in mind, fully synthetic motor oil is even less likely to combust than conventional motor oil and synthetic blends. That said, there is always a risk of combustion if the synthetic oil reaches a high enough temperature.

Just how high, you ask? Most synthetic motor oils have a flashpoint of 450 degrees F; premium synthetic motor oils, however, have flashpoints as high as 700 degrees F (371 degrees C)!

This is actually beneficial to the engine. Imagine that you are driving through an acrid, sweltering desert. Normal motor oil may start to produce more vapors at this point, but synthetic motor oil won’t. Now, this does not mean a car with conventional motor oil is going to explode when it gets too hot inside. It merely means those molecule chains mentioned earlier deteriorate at a much faster pace.

To put it simply, shorter molecular chains have less viscosity than longer ones. Since engines are built with ventilation in mind, this increased level of vapors from conventional motor oil does not pose much of a risk. The only thing you will have to expect is a loss of motor oil volume.

That is where this situation can go bad rapidly. Less oil volume means more friction, which means more heat. Your engine will most likely seize up before it ignites, however.

Synthetic oil does not have this problem, promoting the longevity of your engine, even in more extreme weather conditions.

Will Spilled Oil Catch on Fire?

Yes, spilled motor oil can catch on fire. However, this is not because motor oil is flammable—it is due to combustibility. For example, if the oil that spilled was to pool somewhere exceptionally hot, there is a chance it would ignite. Because of this, you should never drive a car that has been leaking oil.

For starters, your engine will be low on oil, get hotter than average, and may burn the oil left inside.

Best Ways to Store Oil

Sure, engine oil might not be flammable like gasoline, but that doesn’t mean it won’t catch fire. Keep in mind that most flames reach temperatures beyond the flashpoint of oil easily. Should oil come in contact with such heat, it will burn.

This means that you need to be attentive to how and where you are storing oil:

• Provide adequate ventilation. Sure, oil gives off a limited amount of vapors as it gets warmer. While smaller containers of oil are not much of a danger, large amounts could pose a risk of ignition if too much vapors buildup. Prevent that by storing oil somewhere with decent ventilation.
• Keep oil away from ignition sources. If there is flame being used anywhere, move the oil at least 10 yards or 3 meters away from that fire.
• Know how to clean up oil spills properly. Sawdust, kitty litter, and sand are highly absorbent and will prevent leaking oil from spreading. If a lot of oil spills, however, you are going to have to speak with a professional crew with containment facilities.
• Keep oils separated from other combustible and flammable liquids. Storing incompatible liquids near one another is asking for trouble. For instance, you should never place flammables next to oxidizers. If you are low on storage space, use shelf dividers and safety cabinets.

Keep in mind that engine oil is a pollutant, so you will need to store and dispose of it correctly. Do not spill the oil outdoors. Take any old oil to the appropriate waste facilities or station nearby. They will take the oil, even if it is full of kitty litter or sawdust.

How to Deal With an Engine Oil Fire

In the event that your motor oil does catch fire, you should know how to handle the situation. While not flammable, motor oil can ignite easily; when that happens, it is a Class B fire.

Class B fires include flammable liquids, such as gasoline and paraffin. Although engine oil is not classified as a flammable liquid, it is grouped into the same category because of the measures required to extinguish the flames. All Class B fires must be extinguished without water. In fact, dousing an oil fire with water will only make it worse. The flames will burn taller and hotter, and the fire will spread more easily.

In order to put out a Class B fire, you will need a Class B—carbon dioxide—fire extinguisher. The carbon dioxide smothers the oxygen feeding the flame, forcing the fire to die out. If you do not have a Class B fire nearby, you will have to call the local fire department for aid.

Conclusion

So is motor oil flammable? While engine oil has not been classified as a flammable substance, it can be ignited easily when heated beyond its flash point of 350 degrees F. Proper storage and use are necessary to keep engine oils from igniting. Remember to wash away spills, too. That way, you won’t have to worry about any random fires.