If you spend any time working on your car then you know that you have to, occasionally, top off or change the transmission fluid. But is it safe to do this yourself or are you risking a major fire by doing so? The good news is that if you take sensible precautions, dealing with transmission fluid is reasonably safe and you are unlikely to set any major blazes, and here’s why.
Transmission fluid can catch fire, but it is defined by OSHA as a combustible liquid and not a flammable liquid, due to having a flashpoint greater than 199.4 degrees Fahrenheit. The flashpoint of transmission fluid is between 302 and 383 degrees Fahrenheit (150 and 195 Celsius).
So, lets take a look at the reasons why transmission fluid is not technically a flammable liquid, even though it can catch fire. We will also look at how this affects safety when working on your car.
Also read: What Makes Something Flammable?
Table of Contents
Can Transmission Fluid (ATF) Catch On Fire?
Yes, transmission fluid can catch fire, though under most common circumstances – it won’t.
Transmission fluid doesn’t burn as easily as say lighter fluid or gasoline and that means it has to be heated quite a bit before it can light on fire.
But as Thaine Morris tells Quora, it’s entirely possible all the same;
“Yes, it is light mineral oil. I had an F350 Ford truck and had the transmission rebuilt while the engine was being rebuilt at about 200,000 miles. The transmission shop didn’t get the front seal installed properly. Under a heavy load, it popped out, dumping fluid on the hot exhaust crossover pipe. The fire was above the side windows. I was in a dirt field so I drove the truck in circles until the fluid was almost gone, the truck would not pull itself and the fire was almost out, grabbed the fire Extinguisher, jumped out, and put the fire out. I saved the truck but can’t recommend the experience. Yes, transmission fluid can and did catch fire.“
At What Temperature Will It Ignite?
Transmission fluid can catch fire at or above 300 degrees, as that is the estimated flashpoint. When a liquid is heated up to or above its flashpoint, that means that it is releasing enough vapors to catch fire.
But for this to happen a spark or other ignition source must be present.
Because the flashpoint is above 199.4 degrees Fahrenheit, it is labeled by OSHA (Occupational Safety and Health Administration) standard 29 CFR 1910.106 as a non flammable liquid.
Transmission fluid will auto-ignite (spontaneously catch fire) at around 400 degrees Fahrenheit. Auto-ignition means it can catch fire at that temperature without an external ignition source.
That’s pretty hot and as we’ve already noted – it’s not likely to occur under ordinary circumstances.
However, it’s worth noting that welding or grinding can easily produce byproducts that are hotter than this and see transmission fluid catch fire – so, try to keep the two separated.
It is also good to understand that if the fluid ends up in a mist or spray – it may ignite at a much lower temperature than 400 degrees, so try to avoid this whenever possible.
Also read: Is Diesel Fuel Flammable? Yes and No…
What Happens If It Is Burnt?
If the transmission fluid overheats in the transmission, it will pick up a burned smell and this is the moment that you should call a mechanic and book your vehicle in for a service because this isn’t good for it.
The main symptoms of burnt transmission fluid are the scent of smoke/burning, transmission fluid leaking from the transmission and it is darker in color than the usual red, and you’ll be having some problems shifting gear.
It is possible for transmission fluid that leaks from the transmission to end up on a hot surface in the engine and for it to catch fire.
Also read: Is Power Steering Fluid Flammable?
Can It Start A Fire?
Yes, transmission fluid can start a fire. The most likely scenario for it to cause a fire is when it leaks from the transmission onto your engine.
(Though it is unlikely that it will catch fire when you’re topping up the fluid in your vehicle.)
So, it’s very important to follow the proper process for filling your transmission with fluid and to occasionally inspect the transmission and the fluid to ensure everything is in working order.
Transmission Fluid Flash Point
The flashpoint of transmission fluid is between 302 and 383 degrees Fahrenheit (150 to 195 degrees Celsius), depending on the type of transmission fluid.
Again, these are higher than the temperature you will find in the normal day-to-day operation of your vehicle and workshop, but they are achievable by certain activities. It’s best to try and keep potential heat sources and sources of sparks away from the transmission fluid.
Also read: Is Antifreeze/Coolant Flammable? Beware…
Can I Put Transmission Fluid In A Hot Car?
Yes, you can put transmission fluid in a hot car. In fact, you should put transmission fluid into a car with the engine running.
(Though it depends on your definition of “hot”, it would be a bad idea to put transmission fluid into a car that was already on fire, for example).
The right process is for the engine to be running but idling, with transmission set to park and your parking brake on.
See why in this video:
This is because transmission fluid expands when it’s passing through a hot transmission. If you add the fluid to a cold car to the top, then when you turn the car on, the fluid will expand and there will be nowhere for it to go – this will lead to a broken transmission and fluid leaking over the engine.
Transmission fluid can catch fire but is not technically a flammable liquid. The flashpoint point of transmission fluid is around 300 degrees Fahrenheit and that means that transmission fluid is a combustible liquid, not a flammable liquid.
If you weld or grind, then you can easily hit this number and thus, it pays to take some simple safety precautions like those outlined above to ensure that you don’t burn down your workshop or ruin your car rather than get it back up and running perfectly again.