Brake fluids DOT 3 and DOT 4 – what's the difference?
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DOT 3 and DOT 4 are brake fluid specifications set by the Department of Transportation (DOT) in the United States. While both are used in automotive braking systems, DOT 3 and DOT 4 brake fluid for your car do differ. Let's look at them in more detail.
Composition
Both are glycol-based. They contain a mixture of glycols, such as ethylene glycol or diethylene glycol, together with various additives to improve performance and protect against corrosion. However, DOT 4 fluids often have a larger concentration of glycols and different additive packages when compared to DOT 3 fluids.
Boiling points
One of the main differences between these types is their boiling points. DOT 4 fluids typically have a higher boiling point compared to DOT 3. The minimum dry boiling point for DOT 3 is 205°C (401°F), while for DOT 4 fluid it is 230°C (446°F). The wet boiling point, which refers to the boiling point when the fluid contains a certain amount of moisture, is also higher for DOT 4 compared to DOT 3 fluid.
Mixing
Car owners often ask if DOT 3 and DOT 4 brake fluid for BMW can be mixed together without any problems. The answer is yes. This is due to the fact that both are composed of glycols. However, it is essential to note that this will affect the overall boiling point. The two brake fluids can be used interchangeably. If you have a vehicle originally fitted with DOT 4, we advise against using DOT 3 fluid as a top-up. Conversely, vehicles designed for DOT 3 fluid can use DOT 4 without difficulty.
Fluid change interval
Both DOT 3 and DOT 4 require periodic replacement. The recommended fluid change interval may differ depending on the manufacturer's specifications and driving conditions. In general, DOT 4 tends to have a longer service life than DOT 3.
Fluid change maintenance intervals
Brake fluid should be replaced regularly to maintain its effectiveness. The recommended replacement interval varies depending on the type of brake fluid and the vehicle manufacturer's specifications. It is generally recommended that the brake fluid be changed every 1-2 years or as specified in the vehicle's service schedule. This is normally carried out by automotive professionals during routine car brake parts inspections or brake fluid flushes. These procedures involve draining and replacing the brake fluid to maintain its integrity and performance.
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