Is Antifreeze/Coolant Flammable? Beware…

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In the middle of winter, we’ve all been grateful to use a bit of antifreeze to stop our cars from becoming locked up by the cold weather. But is antifreeze a sensible solution to the cold or are we risking something much worse when we use it? Is it possible that antifreeze might stop the engine from freezing but cause it to catch on fire, instead?

Antifreeze is flammable (both ethylene glycol and propylene glycol) according to the National Fire Protection Association (NFPA). It has a flashpoint of approximately 232 degrees Fahrenheit (111 Celsius) and an auto-ignition temperature between 950 and 1245 degrees Fahrenheit, depending on type and concentration.

Let’s take a closer look at antifreeze and it’s fire safety concerns. Here’s what you need to know. 

Your # 1 priority is keeping your family safe. As a firefighter, I recommend everyone has updated smoke detectors that don’t require battery changes, like these ones from Kidde, a fire extinguisher, like this one from Amerex, and a fire escape ladder if you have bedrooms above the first floor, I recommend this one from Hausse.

Also read: What Makes Something Flammable?

What Is Antifreeze?

is antifreeze flammable?

In theory, an antifreeze is anything that you can add to a water-based liquid that lowers the freezing point.

So, for example, water freezes at 0 degrees Celsius (32 degrees Fahrenheit), and an antifreeze might lower that to -10 degrees or 14 degrees Fahrenheit. This is a very useful property as it means you can use it in many circumstances to improve the operation of machinery or vehicles in cold weather. 

Water is, of course, very useful in vehicles and machinery because it’s cheap, cooling, and can be used to remove waste products from processes. The problem is that water is only useful between 0 degrees and 100 degrees Celsius (that’s 32 to 212 degrees Fahrenheit) because of the freezing and boiling points of water. 

Antifreeze allows for this range to be expanded and this is a useful property. 

Here is another explanation:

Also read: Is Diesel Fuel Flammable?

What Is Coolant?

Water and antifreeze can be combined to be used as a coolant. This is true in internal combustion engines, solar water heaters, HVAC chillers, etc., and in this instance, the objective is to ensure that not only will the water not freeze but it won’t expand to fracture the enclosure that it’s being kept in. 

A good quality coolant also has anti-corrosion and anti-cavitation agents that are added to the mix.

These are meant to prevent the circuit, through which the coolant will flow, from excessive wear due to the change in the viscosity of the fluid. 

In fact, while antifreeze is useful for preventing water from freezing up, its main purpose is to make water a more useful heat transfer fluid. This is true because not only does antifreeze lower the freezing point of the solution, but it also raises the boiling point (from 100 degrees Celsius/212 degrees Fahrenheit to 129/265 degrees). 

The first coolant to be developed for use in vehicles was methanol but today, the most common coolants are ethylene glycol and propylene glycol.

In some diesel engines, you may also find propylene glycol methyl ether or glycerol being used. Glycerol is also popular, due to its low toxicity, as antifreeze in sprinkler systems for fire control. 

Is Antifreeze or Coolant Flammable?

Yes, antifreeze is flammable. This includes both ethylene glycol and propylene glycol.

In fact, according to JCM Machine & Coatings, there have been a fair number of engine fires that have been clearly caused by the auto-ignition of antifreeze within the engine. 

Their tests showed that a temperature from 650 to 750 degrees Fahrenheit is enough to cause this autoignition and no spark is required for this.  

They also state that the National Fire Protection Association (NFPA) has formally recognized antifreeze as a flammable liquid. 

Take a look here:

Coolant is a mix of antifreeze and water in a roughly 50-50 blend. Even with the added water content, the coolant is still flammable. 

Evidence shows that it remains just as flammable even with this mixture. We suspect that this is because the ethylene or propylene glycol easily evaporates from the solution and then condenses again nearby. 

However, the tests reported by JCM Machine & Coatings showed that the glycol vapor is even flammable when in the presence of water vapor!

So, we can conclude that it’s very flammable, indeed. 

Also read: Is Brake Fluid Flammable?

Can They Catch On Fire?

Yes, antifreeze will catch on fire.

It auto ignites (as we’ve already seen) in an engine at around 650-750 degrees Fahrenheit. 

What Is The Flashpoint?

The flashpoint of antifreeze, in closed cup tests, is around 232 degrees Fahrenheit (111 Celsius).

That means it’s not likely to catch fire in normal usage, but you should be careful of using antifreeze around naked flames or potential electrical sparks. 

Also read: Is Hydraulic Fluid Flammable? Yes and No…

What About Waterless Coolant?

Waterless coolant requires a special conversion in the cooling system, and it is a solution of a glycol-based liquid without any water.

The advantage of using this coolant is that it boils at 191 degrees Celsius (376 degrees Fahrenheit) which is higher than traditional antifreeze.

However, it catches fire at 650-750 degrees Fahrenheit in the engine in the same way as standard antifreeze. So, waterless coolant is still a fire hazard and can catch fire. 

How Hot Can Antifreeze Get?

Antifreeze or coolant mixtures are meant to be kept at around 160 degrees to 200 degrees and if the temperature is too low or too high – it can mean a problem with the engine.

However, to be precise – antifreeze can get as hot as 650-750 degrees at which point it auto ignites. 

What About RV Antifreeze?

Yes, RV antifreeze is propylene glycol and that means it’s the same as many other brands of anti-freeze.

It’s technically, “combustible” not flammable but we wouldn’t keep it near a naked flame or a spark. 

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