Table of content
19 May 2023 What's the difference between DOT 3 and DOT 4 brake fluids?
Brake fluid is the hydraulic fluid used to create pressure in hydraulic braking systems. When you press down on the brake pedal, the force applied is amplified and transferred into pressure by the master cylinder. The pressurised fluid is then sent to the brake wheel cylinders and the calipers where it is used to force the front and rear brake pads against the metal discs. The friction created when the brake discs and pads come into contact is what causes the car wheels to slow down.
It therefore goes without saying that brake fluid is critical for your safety as without it, you wouldn’t be able to stop your car. Unfortunately, the fluid does go bad over time. It’s hygroscopic, meaning that it easily draws in and absorbs water. The problem with this is that water will significantly reduce the liquid’s boiling point, causing it to become ineffective. The fluid needs to have a high boiling point in order to withstand the extreme heat generated by the brakes. Another common problem is corrosion. Although most products contain inhibitors to prevent oxidation, these inhibitors are gradually broken down and metal parts will start to corrode.
DOT 3 vs DOT 4 brake fluid: what's the difference
“DOT 3” and “DOT 4” are brake fluid classifications. Both DOT 3 and DOT 4 are glycol based. The main difference between the two lies in their respective boiling points. When categorising the fluids both the wet and dry boiling points are taken into account. The wet boiling point is the boiling point when the fluid contains water, and the dry boiling point is when it has not been contaminated with water or other pollutants.
For comparison, DOT 3 fluid typically has a dry boiling point of 205°C, whereas DOT 4 fluid has a slightly higher average wet boiling point of 230°C. This is only a general estimate as the formulas can vary significantly for different products. DOT 4 fluids also have a higher average wet boiling point at 155°C, compared to 140°C, making them safer for hot conditions. For example, they may be more suitable for braking systems that are subjected to higher speeds or heavier loads and, as a result, produce more heat.On the other hand, DOT 4 fluids absorb water at a faster rate and therefore need to be changed more regularly than DOT 3 fluids.
DOT3 is the most common type of brake fluid and is compatible with most cars and pickup trucks. Many of these fluids have a diethylene glycol (DEG) based formula, which makes them cheaper to produce than other types of brake fluids. DOT4 fluids are normally made from a mixture of glycol and borate ester, which helps increase their resistance to boiling.
-40%
ATE Brake Fluid
1l
Article number: 03.9901-6202.2
More
compared to
RRP
£ 28,13
£ 16,73
£ 16,73 for 1 litre
price incl. 20% VAT, excl. delivery costs
Article number: 109452
More
£ 16,53
£ 33,06 for 1 litre
price incl. 20% VAT, excl. delivery costs
Article number: 102718
More
£ 6,63
£ 13,26 for 1 litre
price incl. 20% VAT, excl. delivery costs
Article number: L 05 005
More
£ 5,23
£ 10,46 for 1 litre
price incl. 20% VAT, excl. delivery costs
Article number: MN3003-05
More
£ 4,57
£ 9,14 for 1 litre
price incl. 20% VAT, excl. delivery costs
Looking to buy new brake fluid?
If you’re looking for DOT3 or DOT4 brake fluid for your car, you can find a never-ending selection of products online. You should be able to find the right product for your vehicle by checking the manufacturer’s recommendations in the owner’s manual or by searching using relevant keywords, e.g. “brake fluid for BMW”. Although both types are glycol based, it is still not recommended to mix the two together.
Top products related to this topic:
