Which is better, DOT 4 or DOT 5 brake fluid?
For most modern vehicles, DOT 4 brake fluid is the recommended choice because it balances braking performance, moisture management, and compatibility with ABS systems. DOT 5 is a silicone-based fluid used only in specific classic or specialty applications and is not compatible with DOT 3/4/5.1 systems. Always check your vehicle’s manual or consult a mechanic before changing fluids.
Brake fluid is the hydraulic medium that transmits force from the brake pedal to the brake calipers. The DOT rating signals the chemical composition, boiling points, moisture behavior, and compatibility with seals and materials. Decisions about which fluid to use depend on the vehicle design, climate, and maintenance plan.
Understanding the differences
Key technical contrasts
Here are the essential characteristics that differentiate DOT 4 and DOT 5, and what they mean for everyday driving and maintenance:
- Base chemistry: DOT 4 is glycol-ether (glycol-based); DOT 5 is silicone-based.
- Moisture handling: DOT 4/5.1 absorb moisture over time, lowering the boiling point as water enters the fluid; DOT 5 does not absorb water, which can keep moisture separate but may lead to corrosion if water accumulates in the system.
- Boiling points (approximate): DOT 4 dry around 230°C; DOT 5 dry around 260°C; wet points are lower for both, with DOT 5.1 similar to DOT 4/4.5 variants depending on formulation.
- Seal and system compatibility: DOT 4/5.1 are designed for modern seals and ABS-equipped systems; DOT 5 can be incompatible with some seal materials and original system components. Mixing DOT types is strongly discouraged.
- Maintenance implications: Because glycol-based fluids absorb water, regular changes are common (often every 1–3 years depending on climate and driving). Silicone DOT 5 requires careful handling and is typically not recommended for modern ABS systems.
- Cost and availability: DOT 4 is widely available and affordable; DOT 5 is more expensive and less common, and it is typically used only in certain classic or specialized vehicles.
In practical terms, most drivers will benefit from DOT 4’s established compatibility with modern braking systems and its reliable wet/dry performance. DOT 5 is generally reserved for heritage or highly specialized applications where the vehicle’s original design calls for silicone fluid and a non–water-absorbing option.
Choosing for your vehicle
Practical guidelines
These guidelines help translate the differences into everyday decisions:
- Always follow the manufacturer’s specification for fluid type and specifications (DOT number and whether glycol-based or silicone-based).
- Never mix DOT 5 with DOT 3/4/5.1 in the same braking system. If switching types, perform a full system flush and bleed.
- For modern cars with ABS and advanced braking systems, DOT 4 or DOT 5.1 (glycol-based) is typically the safe choice; DOT 5 is rarely appropriate unless the vehicle was designed for silicone fluid.
- Consider climate and driving style: humid or high-temperature environments heighten the importance of a fluid with a robust boiling point and effective moisture management, which DOT 4/5.1 provide.
- If you own a classic car originally equipped with DOT 5 silicone fluid, confirm seal compatibility and the feasibility of silicone fluid changes with a qualified technician.
Consult the owner’s manual or a trusted mechanic to confirm compatibility, especially for vehicles with modern brake systems or proprietary materials.
Summary
For the vast majority of vehicles, DOT 4 brake fluid is the prudent choice, offering reliable performance, moisture management, and broad compatibility with modern braking systems. DOT 5 silicone fluid remains appropriate only for specific classic or specialty applications where the system is designed for silicone and the manufacturer’s guidance supports its use. Never mix DOT fluids, and follow manufacturer recommendations and service intervals to maintain braking performance and safety.
Is it okay to use DOT 5 instead of DOT 4?
No, you cannot use DOT 5 instead of DOT 4 because they are incompatible; DOT 5 is silicone-based, while DOT 4 is glycol-based, and mixing them will ruin the brake system. You should only use the brake fluid specified by your vehicle's manufacturer, which is typically DOT 4 for most modern cars. Switching from one to the other is a major conversion that requires a complete flushing and a change of seals to be done correctly.
Why you cannot substitute DOT 5 for DOT 4
- Different chemical base: DOT 5 is silicone-based, while DOT 3, DOT 4, and DOT 5.1 are all glycol-based. These two types of fluids do not mix and will cause a system failure if combined.
- Incompatible materials: The seals and components in a system designed for DOT 4 brake fluid are not compatible with DOT 5 fluid.
- Conversion complexity: Switching from DOT 4 to DOT 5 is not as simple as a fluid change. It requires a complete and thorough flush of the entire system, as even small amounts of residue can cause problems.
What to do instead
- Check your manual: Always check your car's owner's manual for the correct brake fluid type.
- Use the correct fluid: If your manual calls for DOT 4, use DOT 4. If you need to switch from DOT 4 to another compatible fluid, you could consider DOT 5.1, which is glycol-based and often a good upgrade that can be used to replace DOT 4 (and DOT 3).
- Avoid mixing: Never mix any brake fluids unless the container explicitly states that they are compatible (e.g., DOT 3 and DOT 4 can often be mixed, but NEVER mix DOT 5 with any other type).
Should I use DOT 4 or 5 brake fluid?
Best practice is to meet the specs on the cap. If you have anti-lock brakes you MUST use Dot 4 (not sure why). But if conventional brakes, you CAN switch to Dot 5. Dot 4 picks up moisture and causes brake fading. Dot 5 has a higher boiling point, doesn't pick up moisture, and won't destroy your paint if you spill it.
What are the disadvantages of DOT 5 brake fluid?
DOT 5 - the silicone-based alternative
While this may seem to be an advantage, DOT 5 also has a higher boiling point and may be less efficient in extreme temperature conditions. In addition, it is not compatible with systems designed for glycol-based brake fluids.
Can you mix DOT 5 and 4?
No, you cannot mix DOT 4 and DOT 5 brake fluid because DOT 4 is glycol-based while DOT 5 is silicone-based, and they are not compatible. Mixing them will cause them to not combine, potentially leading to gelling, seal damage, and compromised braking performance. You should never mix DOT 5 with any other DOT brake fluid.
This video demonstrates what happens when you mix DOT 3, 4, and 5 brake fluid: 56ssubtledriverYouTube · Jan 23, 2022
Why you cannot mix DOT 4 and DOT 5
- Different compositions: DOT 4 is a glycol-based fluid, while DOT 5 is made of silicone. They are chemically incompatible, which is why they separate rather than mix.
- Potential for damage: The incompatible fluids can lead to a variety of problems, including seal damage, gelling (creating a thick, viscous substance), and a significant loss of braking power.
- System failure: Mixing these fluids can lead to brake failure, making it extremely dangerous.
What to do if your system needs fluid
- Check your manual: Always consult your vehicle's owner's manual to determine the correct type of brake fluid it requires.
- Flush the system: If your system contains the wrong type of fluid, a complete flush is necessary to remove all the old fluid before refilling it with the correct type.
- Do not top off: Never simply top off a system with a different type of fluid than what is already in it.
