One part of your braking system that is somewhat overlooked is the fluid. As part of your maintenance routine, and more often than not, you first change the pads or resurface the rotors, but then you might forget a very important liquid that you can’t brake without.
Why go higher?
Most braking systems are capable of using DOT3, however, going up in number means that the brake fluid has a higher boiling point, which means that a higher grade fluid can stand up to or have a more consistent feel even under heavier loads. Evidently, if you go up by whole numbers, from DOT3 to DOT4 or 5, the fluid is more heat resistant. Another benefit that a higher grade has is a thinner fluid. More and more modern cars that come standard with Anti-Lock Brakes Systems (ABS) can take DOT3 fluid but will benefit from DOT4 due to the fluid being less viscous. ABS motors benefit more from DOT4 fluids and up since it will flow through the motor much easier. Even some cars have a traction control system that can also use the braking system, hence, going for a higher-grade fluid can benefit the system.
Although, if you do opt for a higher grade fluid except for DOT5, which is silicone-based, expect shorter longevity as the Glycol Ether and/or and Borate Ester, are prone to absorbing moisture, which means that if your car is stored for long periods of inactivity, or is heavily exposed to the elements, you may need a change sooner than later. That’s the advantage of going for a DOT 3 fluid, it doesn’t absorb moisture as much as DOT4 and DOT5.1, but as mentioned, it has a lower boiling point, so its heat resistance isn’t the best.
A special exception can be handed to DOT5 since it is silicone-based as to not absorb moisture. As per some manufacturers, it is recommended for cars that are stored for long periods of time as is the deal with classic cars. However, being silicone-based means that you cannot mix DOT5 with the other Glycol Ether- and/or Borate Ester-based fluids. You would need to have your entire system flushed in order to use this kind of fluid.
So what brake fluid should I get?
The fluid that we recommend will depend on your usage of the car and its braking systems. For a daily-driven car, DOT3 is enough if you’re not going to be tasking your car and its brakes so much. DOT3 doesn’t absorb moisture as much compared to DOT4 and DOT5.1, so it’s can last longer given the same conditions, however, you do sacrifice braking performance at higher temperatures because of the lower boiling point.
If you are performance driving, or if you find yourself driving spiritedly often and being hard on your brakes, then perhaps it is a good investment to go for a DOT4 or even DOT5.1 fluid. Just know that you will be paying a lot more money and sacrificing the longevity of your brake fluid in comparison to DOT3. Maybe DOT4 or 5.1 isn’t the most cost-effective for your daily driver, however, DOT4 could be a happy medium for most cars nowadays with complex braking systems, even if DOT3 works just fine. A performance car like a Toyota Supra that is constantly and consistently braking hard, will benefit more than let’s say a Toyota Vios, which is a city car that will encounter a lot of unclean and even humid environments and stop and go traffic to name a few.
DOT5, as stated earlier, is a perfect match for cars that spend more time stored in a garage or under a cover because it is silicone-based and will not absorb moisture.
Determine your requirements first, and then go for a brake fluid that matches your use case. Rather than choosing an expensive fluid, make sure that your braking system is in check first. Make sure the brake master cylinders are in check as well as the calipers, rotors, lines, and pads. Perhaps to improve performance you just need a tune-up. That being said, go with what your manufacturer recommends. Check the service manual for the minimum requirements specified, then you can go up from there if you wish. If the owner’s manual recommends you go with DOT4, go for the DOT4.