My car requires DOT 4 brake fluid What happens if I accidentally put DOT 3 brake fluid in it?

Question

I recently learned that my car requires DOT 4 brake fluid, but I accidentally put DOT 3 brake fluid in it while topping off. I’m worried about the potential effects on my braking system. Can anyone explain what happens if I accidentally put DOT 3 brake fluid in my car that needs DOT 4? What should I do next?

Tariq Samer · Accepted Answer

Here’s what you need to know about using DOT 3 brake fluid in a vehicle that requires DOT 4: Boiling Point Differences: DOT 4 has a higher boiling point than DOT 3. This means that under heavy braking conditions, DOT 3 may vaporize sooner, leading to brake fade and reduced braking efficiency. Moisture Absorption: Both fluids absorb moisture, but DOT 4 is designed to handle moisture better due to its higher boiling point. If DOT 3 is used, it might lead to quicker degradation of the fluid and potentially cause corrosion in the braking system. Compatibility: While DOT 3 and DOT 4 are compatible to some extent, mixing them can compromise the performance of your braking system. If you’ve only added a small amount of DOT 3, it may not cause immediate issues, but it’s still not ideal. Immediate Action: If you realize the mistake soon after adding DOT 3, it’s best to flush the brake system and replace it with the correct DOT 4 fluid. This will help ensure your brakes function safely and effectively. Consult a Professional: If you’re unsure about the impact or how to proceed, it’s wise to consult a mechanic. They can assess the situation and recommend the best course of action. In summary, while using DOT 3 in a DOT 4 system isn’t catastrophic if it’s a small amount, it’s advisable to rectify the situation as soon as possible to maintain optimal brake performance.