What’s the difference between DOT 3, DOT 4 & DOT 5 brake fluids?
Brake fluids have different ratings that relate to their boiling points. They’re graded for their boiling point temperatures for when the brake fluid is fresh - it’s dry boiling point, and when it has absorbed water - it’s wet boiling point.
The Department of Transportation defines the ratings - so the ratings are referred to as DOT 3, DOT 4 or DOT 5.
DOT 3 brake fluid has:
- A dry boiling point of approx. 401 degrees Fahrenheit
- A wet boiling point of approx. 284 degrees Fahrenheit
DOT 4 brake fluid:
- Has higher boiling points than DOT 3 brake fluids for both dry and wet
- Should be changed more regularly than DOT 3 brake fluids due to it absorbing moisture faster
- Is recommended in vehicles that will reach higher top speeds or tow heavy loads
There are also now DOT 5 and DOT 5.1 brake fluids available, but they are less common. DOT 5 fluids are silicone based and don’t absorb moisture. They are not suitable for many cars. Never mix DOT 5 brake fluids with other DOT types.
How to change your brake fluid: step-by-step
It can be a slightly challenging process to change your brake fluid, so if you’re not confident in your abilities to do so, it’s always worth having a professional carry out your brake fluid change.
- Park your car on a flat surface and make sure you have plenty of space around to work. Ensure the engine is cool.
- You’ll likely need to get your car up on an axle stand and remove all four tyres to give you the best access.
- Locate the master brake cylinder and remove the cap. If you’re not sure where to find this, refer to your vehicle’s manual.
- Drain the old brake fluid from the brake cylinder. Make sure you have a bucket or old pan ready to catch the old fluid.
- Fill the master brake cylinder with the new brake fluid, using the right brake fluid for your car. You should fill the cylinder up to the ‘full’ line with the new fluid.
- Next, you’ll need to flush each of the wheel cylinders and brake callipers one at a time. To do this, remove the bleed nipple from each calliper and wheel cylinder one by one and drain out the old brake fluid.
- Continue to drain out the old brake fluid until you see the new fluid come through. You’ll need to do this with each of the wheel cylinders and brake callipers.
- Throughout the process, you’ll need to keep an eye on the brake fluid level in the master cylinder and keep it topped up to the ‘full’ line.
- Once you’ve gone through each of the cylinders and callipers, replace the bleed nipples.
- Have one final check of the master brake cylinder and top-up to the ‘full’ line if needed and then replace the cap.
Which brake fluid is right for you?You need brake fluid that you can trust to take good care of your brakes, as well as having the suitable rating for your vehicle. Find the right Mobil brake fluid to help you drive safely for longer.
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