Have you ever been driving and had that “brake” warning light come on? If so, you know how heart-stopping that little light can be!
When this happens, you pull over immediately and give your brakes a little test, right?
They feel OK. At least I hope they do.
But are they? A quick look under the hood tells you that you are low on brake fluids. You find half a can of brake fluid in the trunk but who knows how old it is. Does brake fluid ever get old?
Maybe you decide to drive to your local automotive parts store and get a new can. That’s great but have you ever looked in an automotive shop and seen all the different numbers and brands?
Which are the best brake fluids to use?
What Is Brake Fluid?
Brake fluid is a hydraulic fluid that transfers the force you put on the brake pedal into amplified pressure. This pressure operates the wheel cylinders and pistons to slow the vehicle.
Most brake fluids are either glycol-ether or synthetic glycol. DOT5.0 is a silicone-based brake fluid that cannot be mixed with other types of brake fluid.
Does Brake Fluid Go Bad?
If that open can of brake fluid in the trunk or garage is more than a year old, ditch it.
If you aren’t sure about the age, you should probably toss it.
Brake fluid absorbs water from the air. That means it can make the brake lines rust and put water in the system when what you need is a hydraulic fluid.
My father’s trick was to write the date on the can, so he knew when to throw it out.
What is the Difference Between DOT3 and DOT4?
DOT stand for the Department of Transportation. The main difference between DOT3 and DOT4 is the boiling point of the fluid.
Most people never come close to reaching the maximum boiling point in their everyday commutes or grocery store runs. But it can happen on mountainous roads. This is why you must use the correct type of fluid that the manufacturer dictates.
Brake fluid is also prone to water absorption. Both DOT4 and DOT3 will absorb water. This is why you should discard any brake fluid that is in an opened container after one year.
If the container is still sealed by the manufacturer, it is safe to use. But you should throw out that old can of brake fluid that has been sitting in your garage for a few years.
DOT3 is more likely to absorb water than DOT4. You can always go up a number but should only use a lower number brake fluid in an emergency.
For example, if your car normally uses DOT3, it is fine to use DOT4 or even DOT5.1. But if your car calls for DOT5.1 and the only brake fluid available is DOT4, you can use it. But you should have the brake system flushed and the proper brake fluid replaced as soon as possible.
Does it Matter Which Brand of Brake Fluid I Use?
Like motor oil and gasoline, everyone has their favorite brands. Some brands offer special additives which offer a higher boiling point. They contain anti-foaming ingredients, or they are less prone to absorb water.
It is far more important that you use the correct DOT number for your car or use a higher number. Most vehicles have this information in their owner’s manual. Some have the minimum DOT number listed directly on the brake master cylinder reservoir cap.
If all else fails, you can google it. You will be sure to find this information about your exact year and model. You can also ask your local mechanic or call the dealership.
How Do I Choose Brake Fluid?
You may have heard old-timers say, “Brake fluid is brake fluid is brake fluid.” I know I’ve heard my dad say this, but this isn’t 100 percent true. When you hear this, they’re mainly referring to brands.
First, you need to know what type of brake fluid your vehicle uses. Each can of brake fluid has a number on it, such as DOT3 or DOT4.
Hopefully, you have your owner’s manual, or your cell phone and you can quickly determine which one your car uses.
On occasion, the cap to the brake master cylinder will tell you which type of brake fluid to use.
If you can’t find this information, don’t sweat it. The DOT3 brake fluid or DOT4 brake fluid is simply referring to the boiling point.
You will most likely never get anywhere close to the boiling point in everyday use. You may on certain types of roads. It’s important to find out and use the manufacturer’s requirement for your car.
For many years, there really was only one type of brake fluid. But cars have changed so much over the years that there are now brake fluids reading DOT4 and even DOT5 and DOT5.1.
What You Need to Know about Brake Fluid
There are 4 different types of brake fluid, each one with a different boiling point, and only one (currently) that is vastly different.
These four brake fluid types are:
That 5.1 number is very confusing. Many mechanics wish that the DOT had chosen another number. But it’s there and we must get used to it.
The main difference between all these numbers is the boiling point and all the numbers.
Except for 5.0 which are either a glycol based type of fluid. They can also be a synthetic version of a glycol based fluid.
DOT5, sometimes called DOT5.0 is a silicone-based fluid. It cannot be used or mixed with any other type. You can not use a different type if your vehicle says it needs DOT5.
Some manufacturers change the color to purple to prevent people from using DOT5 in cars that are not designed for it.
All other types, including DOT3, DOT4, and DOT5.1, should be a clear color or a light amber color. Similar to the color of clean motor oil.
If your vehicle has purple fluid in the brake master cylinder, you CANNOT use anything else but DOT5.
Likewise, if your vehicle has a clear or amber-colored fluid, DO NOT use a purple fluid.
You can use DOT4 in a car that uses DOT3, but only in an emergency should you use DOT3 in a car that has or uses DOT4.
Some Quick Facts about Brake Fluid
You don’t need to be a chemist to pick the best brake fluid for your car. All you need is a few facts.
- You can mix brands.
- Some people might tell you that you should never mix brands, but this isn’t true. It’s the DOT number that is most important. As long as you aren’t adding DOT5 when your car doesn’t have that already, you will be fine for a short time. If you mix Lucas DOT4.0 brake fluid with your Wagner DOT4.0 brake fluid, it’s OK.
- Is it OK to mix DOT3 and DOT4 Brake fluid?
- Even if you mess up and add the wrong type of fluid, you will be OK. Remember that as each number goes higher, the boiling point of the brake fluid goes up as well. So, if your vehicle has DOT4 in it right now and you accidentally add DOT3, it’s fine. This will mean that the brake fluid is now working at a DOT3 boiling point.
- What happens if I use the wrong brake fluid?
- If you later discover that you should have used DOT4, you can always get the brake system flushed and have the correct fluid added. I believe that driving with a bit of DOT3 brake fluid, rather than DOT4, is far better than being low on brake fluid.
- Why is the brake fluid I bought purple and the stuff in my car is amber?
- This is about the only mistake that matters. DOT5 brake fluid is made purple and all other DOT numbers are clear-ish or amber-colored. These two should not be mixed. DOT5 brake fluid is synthetic, the others are not. If you see purple brake fluid in your car, buy DOT5. If your vehicle has amber-colored brake fluid, buy DOT5.1, DOT4, or DOT3.
How To Change Brake Fluid
As simple as brake fluid is, the different numbers, colors, and use-by dates can be confusing. Especially if you only top off your vehicle one every three years or so.
Some find it easier to make a small tag and put it on the glove box door with the correct brake fluid type. Others like to mark the container of brake fluid with the date they purchased it. Just make sure you discard it after about a year!