motoring

A Quick Guide to Car Brake Fluid

March 24, 2021

What Is Brake Fluid?

Brake fluid is a hydraulic fluid used to apply pressure to the brake callipers and stop a vehicle. It makes it easy for drivers to brake without using extreme force to halt such a heavy, fast-moving object. The fluid also absorbs a lot of the action’s pressure, which reduces wear on the car and increases mechanical longevity.

Brake fluid is not an optional extra and without it, a car does not work properly. Without brake fluid in your brake system, you cannot stop your vehicle. With that vital detail covered, the next step is identifying which brake fluid to use.

Most cars will use DOT4 brake fluid or DOT5.1 brake fluid.

There is also a rarer form of brake fluid, DOT5, which we will cover later.

What Are The Differences Between DOT4 and DOT5.1 Brake Fluid?

There is only one major difference between DOT4 and DOT5.1 brake fluid:

The Boiling Point

When a vehicle is driven, the engine heats up, as do the other components. If the brake fluid gets too hot, it can hit boiling point.

You do not want your brake fluid boiling. This can stop the brakes from working correctly, if not altogether. Even if they continue to work, the wear-and-tear alone from the brake system’s lack of lubrication (caused by a lack of hydraulic pressure) can be enough to cause irreparable damage to your vehicle.

DOT5.1 has a higher boiling point than DOT4, making it better for cars that experience higher temperatures.

In summary:

If you’ve got a large-engined vehicle or drive in hot climates, you’ll likely need DOT5.1 to avoid your brake fluid boiling.

If you have a smaller-engined vehicle, such as a standard family car, you’ll probably only need DOT4.

Which Brake Fluid Do I Need?

Your car needs a brake fluid that will provide it with a high enough boiling point to avoid any problems with damaging car parts. This can either be DOT4 or DOT5.1, depending on your vehicle requirements. To find this information, you need to check your owners manual. There will be information about using brake fluid and which DOT to buy.

How Can I Tell If My Brake Fluid Is Running Low?

Inside your car’s engine bay, you’ll find the brake fluid reservoir. You can identify the reservoir by the cap. The brake fluid reservoir cap is very distinctive. The image displays a circle (the wheel) with two semi-circles on either side (the brake pads). It will look a little something like this — ( O ).

The brake fluid reservoir is transparent. It also has two markers: min and max. If you need to top up your brake fluid, you’ll notice the fluid inside the brake fluid reservoir is below the “min” marker.

What Happens If I Put the Wrong Brake Fluid in My Car?

Nothing. And everything.

Almost all vehicles can use DOT4 and DOT5.1 brake fluid as the components and systems of all common commercial and private vehicles can accommodate both brake fluids. DOT4 and DOT5.1 brake fluids are also compatible with each other.

You can put DOT5.1 as a top-up in a car using DOT4.

The problem arises when you mix the rarely used DOT5 with DOT4 or DOT5.1. DOT5 is a silicone-based hydraulic fluid, most often used in heavy-duty or high-performance vehicles.

DOT5 is not compatible with DOT4 and DOT5.1, which are poly-glycerol based. The fluids will not combine, and driving with this mixture can cause heavy damage to your brake system.

So, if you’ve filled your car with DOT4 when you needed DOT5.1, you won’t have caused any lasting damage providing you haven’t been driving the vehicle to the edge of its performance. The brake fluid itself won’t cause any harm; it’s only when the brake fluid isn’t up to the challenges that the vehicle demands of it that you’ll experience problems.

However, if you’ve accidentally topped up a DOT5.1 system with DOT5, you’ll need a complete hydraulic fluid flush to replace the contaminated system.

Brake fluid is simple to use and understand. Anyone can top up their brake fluid without risk of incident, providing they’ve read their owner’s manual to make sure they’re using the right DOT. Changing your entire system (brake fluid flushing and replacement) is a different story, however, and will require the help of a mechanic.

At the end of the day, always make sure the brake fluid is handled correctly, even if that means getting help.