Buy DOT 4 brake fluid
What to buy
Buy a factory-sealed bottle labeled DOT 4 when the owner’s manual or the master-cylinder cap specifies DOT 4 brake fluid. That marking is the buying rule. If those sources add a tighter grade—low-viscosity DOT 4, ISO 4925 Class 6, a high-boiling racing DOT 4, or DOT 5.1—match that extra mark instead of a generic DOT 4.
Confirm the vehicle spec first
The right fluid depends on model year, market, trim, and the braking hardware, including whether the vehicle uses anti-lock brakes and electronic stability control. Read the cap and the manual for that vehicle. If they disagree with an aftermarket label or a verbal suggestion, follow the vehicle maker.
DOT is a U.S. Federal Motor Vehicle Safety Standard 116 grade for hydraulic brake fluid. DOT 3, DOT 4, and DOT 5.1 are glycol-ether fluids in the same chemical family. DOT 5 is silicone. Silicone DOT 5 is not a substitute for DOT 4, and the two must not be mixed. A system filled with silicone needs silicone until it is fully converted under the maker’s rules.
What the DOT 4 grade means
DOT 4 is a glycol-ether hydraulic fluid that must meet a minimum dry boiling point of 230 °C and a minimum wet boiling point of 155 °C. Dry boiling point is the rating of unused fluid. Wet boiling point is the rating after the fluid has absorbed moisture, which is the figure that matters in service. Those values are the legal floor; some bottles exceed them. A higher boiling point resists vapor in the lines during hard or repeated stops, when heat soaks into the calipers.
Brake fluid is hygroscopic: it absorbs water from air. Absorbed water lowers boiling point and can promote corrosion inside the hydraulic system. Buy fresh, sealed fluid. An opened or long-stored bottle can already hold moisture even if it still says DOT 4.
When another grade changes the purchase
Cap or manual says DOT 4: buy DOT 4, or the extra DOT 4 variant named there. Cap or manual says DOT 3: DOT 4 is often allowed as a glycol fluid with a higher boiling-point class; treat an explicit ban in the manual as binding. Cap or manual says DOT 5.1: that is also glycol-ether, with higher minimum boiling points (260 °C dry, 180 °C wet). Buy DOT 5.1 when that is the listed grade. Cap or manual says DOT 5: that is silicone. Do not buy DOT 4 for that system. ABS, ESC, or ESP systems that specify low-viscosity DOT 4 or ISO 4925 Class 6: buy that low-viscosity grade so the control valves meter fluid as designed. Track use or a racing DOT 4: only when the vehicle still requires a glycol DOT 4 and the bottle is compatible with any ABS or stability system on the car.
Grade Base Minimum dry boiling point Minimum wet boiling point Buy with a DOT 4 system? DOT 3 Glycol ether 205 °C 140 °C Often acceptable if the manual allows a glycol upgrade; DOT 4 Glycol ether 230 °C 155 °C Yes, when DOT 4 is specified; DOT 5.1 Glycol ether 260 °C 180 °C Same family; use 5.1 when the maker lists it; DOT 5 Silicone 260 °C 180 °C No; do not mix with glycol fluid
What to check on the bottle
The DOT 4 mark, plus any extra grade the vehicle lists (low-viscosity, Class 6, racing). An intact factory seal. Skip a container that has been opened or looks previously used. A printed manufacture or fill date when one is present, and prefer recent stock. Enough unused fluid for the job. A reservoir top-up uses little; a full bleed and flush uses more. Buy only what you will open for this service. A warning that glycol fluid damages paint. Wipe spills off bodywork immediately.
Topping up versus a full change
A slight drop in the reservoir as the pads wear is normal. In a glycol-filled DOT 4 system, topping up with fresh sealed DOT 4 is the usual step when the level is only a little low and there is no leak. A large drop, a warning light, a soft pedal, or fluid on a wheel points to inspection first. Adding fluid can hide a leak or a failing hose, caliper, or master cylinder.
Do not mix DOT 4 with silicone DOT 5. Do not reuse leftover fluid from an open bottle for a later service. Follow the vehicle’s maintenance schedule for a complete fluid change; that interval is set by the maker for that model year and braking system.
What this page cannot settle
This guidance cannot name a brand, part number, bottle size, price, or test ranking for a specific vehicle. Those details vary by market and stock. If the cap, the manual, and a service bulletin conflict, use the latest instruction from the vehicle maker. If the system has already been filled with silicone DOT 5, stay with DOT 5 until a complete conversion is done and the maker allows a glycol fill.