Complex vehicle systems require various fluids to ensure the proper functioning of their mechanical components. Among the most important are engine oil and brake fluid . Although both play a crucial role in vehicle performance, they differ significantly in their properties, chemical composition, and functions. This article will discuss the differences between these two fluids and answer frequently asked questions about their maintenance and replacement.
1. What is motor oil and what is its function?
Engine oil is one of the most important fluids in a car, as it lubricates the moving parts. In an internal combustion engine, pistons, valves, crankshafts, and bearings are subjected to friction and high temperatures. Insufficient lubrication can lead to metal wear and serious engine damage.
The main functions of motor oil
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Lubrication: Reduces friction between moving engine parts.
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Cooling: Absorbs heat from the high-temperature engine components and transfers it to the crankcase.
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Cleaning: Collects carbon particles, metal shavings, and impurities.
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Seal: Fills the gap between piston and cylinder to maintain pressure.
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Corrosion protection: Forms a protective layer that prevents oxidation and rust.
Composition of motor oil
Motor oil typically consists of two components:
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Base oil: Makes up approximately 80–90% of the total oil composition. It can be mineral, synthetic, or semi-synthetic.
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Additives: Compounds used to improve antioxidant, purifying, corrosion-resistant and temperature-regulating properties.
2. What is brake fluid and what is its function?
Brake fluid is a hydraulic fluid that transmits braking force in the braking system. Unlike engine oil, which acts as a lubricant, brake fluid must transmit the force from the brake pedal to the brake pads and calipers without compressing, so that the vehicle can stop quickly .
Function of brake fluid
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Power transmission: Conversion of mechanical brake pedal pressure into hydraulic pressure.
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High-temperature resistance: During heavy braking, the temperature of the brake pads can exceed 200 °C. The brake fluid must retain its effectiveness at this temperature without evaporating.
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Corrosion protection: Protects metal components such as pistons, cylinders and brake lines.
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Chemical stability: Resistant to moisture and oxidation.
Types of brake fluid
Brake fluids are generally classified according to the standards of the US Department of Transportation (DOT):
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DOT 3: Based on ethylene glycol, it has a low boiling point and is suitable for normal vehicles.
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DOT 4: The most commonly used type in modern cars, it has a high boiling point.
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DOT 5: Silicone-based material, not compatible with DOT 3 and 4 and suitable for certain vehicles.
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DOT 5.1: A group of ethylene glycols with a high boiling point and low viscosity.
3. Key differences between engine oil and brake fluid
| Special feature | Engine oil | brake fluid |
|---|---|---|
| Main areas of application | Engine lubrication and cooling | Energy transfer in the braking system |
| Chemical properties | A mixture of hydrocarbons with corrosion protection additives | glycolic acid or silicone compounds |
| Viscosity (concentration) | High, varies depending on the temperature | Low, almost constant |
| Heat resistance | Temperatures can reach approximately 150-180 degrees Celsius. | More than 250-300 degrees Celsius |
| Compressibility | It’s somewhat compressed. | Almost incomprehensible |
| hygroscopic | strange | High (especially DOT 3 and DOT 4) |
| Replacement period | Usually every 5,000–10,000 kilometers | every two or three years |
| the effects of failure | Increased wear and reduced engine performance | Poor braking performance increases the risk of accidents. |
4. Why can’t you use engine oil instead of brake fluid?
Some might think that, since both substances are “oils,” they can be used interchangeably in emergency situations. This is a serious misconception. The reason lies in the fundamental differences in the physical and chemical properties
of these two liquids.
The main reasons for preventing substitutions are:
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Motor oil has no hydraulic properties. Although it can be compressed, it cannot effectively transmit pressure.
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Engine oil operates at low temperatures , burns quickly, and evaporates in the braking system.
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Engine oil can damage the seals and O-rings of the brake system, as the rubber materials in the brakes are only compatible with a specific chemical composition of the brake fluid.
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There is a risk of complete brake failure, which could lead to an accident .
Therefore, under no circumstances should motor oil be used as a substitute for brake fluid.
5. The influence of temperature on the properties of oil
Both engine oil and brake fluid must maintain stable performance at high temperatures, but they react differently.
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Engine oil loses viscosity at high temperatures, making it more flammable and susceptible to oxidation. For this reason, standards such as SAE 5W-30 and 10W-40 were developed to regulate viscosity at different temperatures.
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Even at very high temperatures (250 to 300 degrees Celsius), the brake fluid should not evaporate , as the formation of vapor bubbles in the brake circuit can lead to a drop in pressure and slippage of the brake pedal.
6. Important tips for engine oil maintenance
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Regular replacement: Replace the part according to the vehicle’s operating manual or every 5,000–10,000 kilometers.
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Check the engine oil level: Use the dipstick to check it at least once every two weeks.
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Use the correct oil filter: A dirty filter can lead to re-contamination of the oil.
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Select lubricants according to SAE and API standards.
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Pay attention to the color of the oil: if it is too dark or too thick, it should be replaced.
7. Procedures for brake fluid maintenance and replacement
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Change it every two to three years or every 40,000 kilometers.
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Do not leave the brake fluid reservoir cap open, as it will absorb moisture from the air.
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Different DOT ink colors must not be mixed unless approved by the manufacturer.
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Check the brake fluid level : A low level may indicate a leak in the system.
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Do not use expired or already opened essential oils, as these will lose their acne-fighting effect .
8. Compare the cost and importance of a replacement.
From an economic standpoint, engine oil is generally more expensive and requires a larger quantity (3 to 5 liters) per oil change, while brake fluid requires less than one liter. However
, from a safety perspective, brake fluid is far more important. Even a brief brake failure can lead to serious accidents.
9. Differences in color, smell, and texture
| Special feature | Engine oil | brake fluid |
|---|---|---|
| base color | Gold or amber | From colorless to light yellow |
| nephritis | A specific smell of oil or chemicals | Strong ethanol smell |
| texture | fat and heavy | Thin and soft |
| The color changes over time. | Darkness and blackness | brown or dark yellow |
10. Frequently Asked Questions
Can brake fluid be mixed with water or other liquids?
No. Water lowers the boiling point of brake fluid and leads to vapor formation in the system. Mixing it with other fluids is dangerous.
What happens if the brake fluid level is too low?
If the brakes feel spongy or the brake pedal is fully depressed, this may indicate a leak in the brake system and requires immediate inspection.
When should I change my engine oil?
Depending on the type of engine oil and operating conditions, the oil change interval is usually between 5,000 and 10,000 kilometers. For modern vehicles with synthetic engine oil, it can be up to 15,000 kilometers.
What should you do if engine oil gets into the brake system?
The system must be completely emptied and cleaned, otherwise the seals will be damaged and the braking function will be impaired.
11. Final Conclusion
In summary:
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The function of engine oil is to lubricate and cool the engine .
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Brake fluid is used for power transmission in the braking system and is resistant to high pressure and high temperatures.
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The improper use of components, especially in the braking system, is dangerous and irreversible.
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Regular maintenance and timely oil changes extend the lifespan of your vehicle and ensure your safety while driving.