If you’ve handled engine oil and other automotive lubricants before, you may have wondered – is this stuff flammable? Especially when changing the oil on a hot engine, the thought crosses your mind. The good news is engine and motor oils are not extremely flammable. But under the right conditions, common motor oils used in cars, motorcycles, lawnmowers, boats, and other vehicles can indeed ignite and burn.
So is engine oil flammable? The short answer is yes, most standard motor oils are technically considered flammable liquids. But their ignition temperature is far higher than gasoline, ethanol and other fuels. The exact flammability depends on the oil’s flash point – the lowest temperature it gives off vapors that can catch fire with an ignition source present. Conventional and synthetic blends have flash points from 350°F up to 420°F. Higher performance synthetics designed for extreme conditions can have flash points over 500°F, making them much less prone to igniting.
In this comprehensive guide, we’ll cover everything you need to know about motor oil flammability, including:
- How flash point and fire risk changes between different types of engine oils.
- The reasons why motor oils contain flammable ingredients in the first place.
- Best practice tips for safe storage and handling of combustible lubricants.
- Non-flammable oil alternatives for specialized applications.
- And most importantly – what all this means in practical terms for your vehicle’s engine oil.
So let’s get right into it!
Table of Contents
Why Motor Oil Flammability Depends on The Flash Point?
The key characteristic that determines how easily a fluid like engine oil can ignite is the flash point. This is literally the lowest temperature at which the oil gives off enough flammable vapors to catch fire if there’s an ignition source present.
Gasoline has a very low flash point, around -45°F, which is why gas vapor is so easy to light with a match or spark. The flash point of motor oil is much higher, but still low enough for the oils to be labeled as flammable liquids.
By definition, a flammable liquid has a flash point below 100°F. Oil with a flash point up to 199°F is considered a combustible liquid. Both are regulated similarly for safe handling by OSHA and other agencies.
So what are some typical flash points for common motor oils?
- Conventional SAE 10W-30 oil – 350 to 400°F
- Full synthetic 0W-20 oil – 375 to 420°F
- Synthetic blend 5W-30 oil – 360 to 400°F
As you can see, there’s quite a range depending on the specific formula, but most fall in the 350°F to 420°F range.
For reference, here’s how motor oil flash points compare to other flammable fluids:
- Gasoline – -45°F
- Ethanol – 55°F
- Diesel fuel – 125-150°F
- Cooking oil – 585°F to 680°F
Engine oil needs a much higher temperature to vaporize and ignite than gasoline. But oils still fall into the flammable category, unlike cooking oils that have flash points above 500°F.
The difference between conventional and synthetic motor oils in terms of flammability is minor. Fully synthetic oils formulated for extreme high temperatures and racing applications can have flash points 100°F or more higher.
For everyday use in street vehicles though, both conventional and synthetic oils give off flammable vapors before reaching the 400°F range.
Next, let’s look at why these motor oils contain flammable ingredients in the first place.
The Flammable Compounds in Motor Oil – And Why They’re Added
When you think about it, why would an engine lubricant – that needs to withstand tremendous heat and pressures – be designed in a way that it could potentially catch on fire?
It may sound counterintuitive, but there are specific reasons why motor oils contain compounds that give them a relatively low flash point:
1. Petroleum Origins
Even though formulations vary, essentially all motor oils start with a base of hydrocarbon compounds derived from crude oil distillation. Smaller hydrocarbon chains with fewer carbon atoms tend to be more volatile and flammable. Yet they are important for fluidity and performance.
Most engine oils use a mix of paraffinic and naphthenic petroleum oils as the base stock. Synthetics and higher performance oils shift more towards polyalphaolefins (PAOs) which are less flammable, but made from petroleum feedstocks nonetheless.
2. Operating Temperatures
Motor oil needs a high boiling point and ability to maintain viscosity at high temperatures – like the 300°F plus found inside a running engine. But the base oil compounds that meet these criteria still have a flash point and flammability risk short of that operating temperature.
Detergents, antioxidants, anti-wear additives, viscosity index improvers and other performance packages blended into oils also influence flammability:
- Detergents increase flash point but can also raise volatility at very high temperatures.
- Some antiwear additives like zinc dialkyldithiophosphate (ZDDP) act as antioxidants, while others reduce flash point.
- Viscosity index improvers designed for high temperature stability degrade more easily, producing volatile byproducts.
Formulating a high quality motor oil means balancing flash point and fire risks against durability, sludge prevention and other performance factors. There are always tradeoffs with flammability being one of them.
Safe Practices for Handling Flammable Motor Oils
Now that you know why motor oils have a relatively low flash point, what does this mean in terms of safe handling?
The good news is taking some simple precautions will minimize any fire risks when working with engine oils:
- Keep oil tightly sealed in approved containers, away from any sources of ignition. This includes flames, engine heat, hot surfaces over 400°F, and sparks from tools or welding.
- Avoid storing large amounts of oil long term. The more volatile, flammable fractions can separate over time.
- Check for oil leaks which can soak into rags, cardboard and other absorbents. Dispose of properly.
Cautious Oil Changes
- Allow the engine plenty of time to cool before changing the oil, and drain the oil while it’s warm but not near operating temperature.
- Keep the work area clean and free of spills. Clean up any drips or leaks right away.
- Place drain pans and tools on concrete or dirt if possible, not on dry grass or brush.
Handle Rags and Absorbents With Care
Oily rags and other materials with motor oil residue generate heat as they oxidize, potentially igniting if the pile grows too large before disposal.
- Allow rags to dry in the open air before disposal, don’t bundle up oily rags in a pile.
- Consider placing rags in a metal bucket with water and detergent instead of letting them fully dry.
- Change out floor dry, cat litter or other absorbents frequently after spills.
Wear Protective Equipment
- Wear gloves, safety glasses and protective clothing if handling hot oils or used motor oil which contains more volatile compounds.
- Avoid prolonged skin contact with oils to prevent irritation. Wash up with soap and water after handling.
- Wear an organic vapor respirator when draining or emptying large volumes of oil.
Recycling & Safe Disposal
Never pour used motor oils down a drain, storm sewer or directly onto the ground or in waterways. Recycle it properly:
- Many auto parts stores, repair shops and waste management agencies accept used oil for recycling.
- Use approved containers and labels when collecting oil for recycling. Keep it sealed.
- Consider turning old oil into home heating oil if regulations allow through authorized waste oil furnace vendors.
By following these best practices, you can safely store and handle automotive oils as well as maintain and repair vehicles requiring oil changes. Taking sensible precautions greatly minimizes any fire hazards.
Now let’s look at some specialized oils engineered to be non-flammable.
Non-Flammable Alternatives To Engine Oils
For applications where any fire risk is unacceptable, such as turbines, compressors and hydraulic equipment, there are lubricant options formulated to remove flammability:
1. Highly Refined Mineral Oils
Hydraulic oils and some industrial lubricants undergo additional refinement like hydrogenation to produce a more stable mineral oil with a very high flash point over 550°F.
2. Phosphate Esters
Synthetic phosphate esters used in turbine engines and jet engine oils act as flame retardants. They degrade instead of sustaining a flame and have flash points over 500°F.
3. Silicone Oils
Inert silicone oils maintain excellent viscosity and lubricity up to 600°F. Their non-carbon structure gives them a flash point exceeding 575°F.
4. Vegetable Oils
Biodegradable vegetable-based oils like canola oil and sunflower oil offer good lubrication for light duty applications. Refining removes impurities to increase flash point above 600°F in most cases.
5. Synthetic Esters
Synthetic esters made from vegetable oils but molecularly-engineered for extreme durability provide the best of both worlds. Their stability results in flash points over 500°F. Popular in jet engines.
For specialized electric vehicle applications, even oils with flash points in the 500°F range may be avoided in favor of inherently non-flammable coolants and lubricants.
But for virtually all conventional street vehicle engines, the lubricant fire risk just doesn’t justify these specialty oils. Especially considering they come at a very steep cost premium.
The Bottom Line
To summarize everything we’ve covered about motor oil flammability:
- Yes, nearly all standard engine oils – including conventional and synthetic blends – have flash points in the 350°F to 420° range, making them technically flammable liquids.
- But this practical fire risk is very low during normal vehicle operation and maintenance.
- The minimal flammability ultimately comes from the refined petroleum base oils and additive packages required to meet engine durability demands.
- However, taking proper precautions when handling used oil or working around hot engines minimizes any real-world fire hazard.
So in your vehicle’s engine, motor oil works extremely well despite a bit of underlying flammability, especially when you follow safe handling protocol.
For specialized industrial applications where no flammability is acceptable, highly refined mineral oils or synthetic fluids offer non-flammable alternatives.
So in summary, while standard motor oil is technically combustible, the practical risks are negligible in engine operation as long as you take reasonable precautions when handling it – which we’ve covered in detail here.
Now you can feel confident that the conventional or synthetic oil in your vehicle poses very minimal actual fire hazards – despite what the technical flash point data may imply out of context.
Just use common sense when changing and disposing of hot oil, wear protective gear to prevent skin contact when handling large amounts of used oil, and allow proper ventilation in confined areas.
Following the simple best practices outlined here for storage, oil changes, rags, absorbents, protective equipment, and recycling will let you safely reap the benefits of quality motor oil in your engine.
I hope this guide gave you a full understanding about engine oil flammability! Let me know if you have any other questions.