2018-2019 Audi S5 Brake Fluid Type and Flush Interval

By Core Brake Parts Tech Team — Circleville, OH warehouse

The 2018-2019 Audi S5 calls for brake fluid that meets Audi/VW standard VW 501 14, a low-viscosity DOT 4 fluid. If you cannot get a fluid carrying that approval, the owner's manual allows a high-grade fluid that meets FMVSS 116 DOT 4, Class 6. Audi's published maintenance schedule for the 2018 model year says to change the brake fluid every 2 years on all vehicles, with no mileage limit attached.

That is the short answer. The rest of this guide explains why the S5 wants a low-viscosity fluid, why the interval is based on time and not miles, how to tell when the fluid is overdue, and what to plan for if you are doing pads at the same visit.

What Fluid the 2018-2019 S5 Uses

The 2018-2019 S5 (Coupe, Sportback and Cabriolet) is built on Audi's B9 platform, shared with the A4 and A5 of the same years. The B9 owner's manual text is direct: the brake fluid must meet VW 501 14. If that is not available, a fluid of equivalent quality may be used as long as it meets FMVSS 116 DOT 4, Class 6. The manual also notes the reservoir sits under a cover on the driver's side, and the level must stay between the MIN and MAX marks.

"Class 6" refers to ISO 4925 Class 6, the international grade for low-viscosity DOT 4 fluid. Fluids sold for these cars usually say "DOT 4 LV" on the bottle and list VW 501 14 or ISO 4925 Class 6 in their approvals. For example, the Pentosin DOT 4 LV data sheet lists FMVSS 116 DOT 4, ISO 4925 Class 6 and SAE J1704, and Ravenol lists VW 501 14 among the OEM recommendations for its DOT 4 LV fluid.

Why Low Viscosity Matters on This Car

Federal standard FMVSS 116 caps DOT 4 fluid at 1,800 mm2/s of kinematic viscosity at -40 C. That is thick enough to slow down a modern stability-control hydraulic unit, which pushes fluid through small valves and passages many times per second when ABS or stability control is working. A low-viscosity DOT 4 is formulated to flow far more freely in the cold. The Pentosin DOT 4 LV sheet rates its fluid at 700 mm2/s or less at -40 C, and Ravenol rates its DOT 4 LV at a maximum of 750 cSt at -40 C. Both describe their fluid as intended for vehicles with ESP and ABS.

In practice, a regular DOT 4 will still stop the car on a warm day. The reason to use the specified fluid is how quickly the ABS and stability control can modulate pressure in cold weather, which is exactly when you need them. Since a flush replaces nearly all of the fluid anyway, there is no reason to put anything but a VW 501 14 or DOT 4 Class 6 fluid in an S5.

Do not use DOT 5 (silicone) fluid. It is a different chemistry and is not what this system is designed for. Ravenol also warns that its glycol DOT 4 fluid is not suitable for mineral-oil brake systems, a reminder that brake fluids are not interchangeable across chemistries.

Why the Interval Is Every 2 Years, Not by Mileage

Glycol-based DOT 4 fluid is hygroscopic: it absorbs moisture from the air through hoses, seals and the reservoir vent, whether you drive the car or not. That is why FMVSS 116 requires every bottle to carry a warning to keep the container clean and tightly closed to prevent absorption of moisture.

Water lowers the boiling point. FMVSS 116 sets two boiling-point minimums for DOT 4:

• Dry (new fluid): at least 230 C (446 F)
• Wet (fluid humidified to about 3.7 percent water): at least 155 C (311 F)

Low-viscosity fluids for these cars often exceed those minimums when new. Pentosin rates its DOT 4 LV at 265 C (509 F) dry and 170 C (338 F) wet. But the direction is always the same: the longer the fluid sits in the car, the closer it moves to the wet number. On an S5, a hard run down a mountain grade or a track day can heat the calipers enough to boil moisture-laden fluid. The B9 owner's manual warns that if the brake fluid is old, bubbles may form in the brake system during heavy braking. Vapor bubbles compress, so the pedal goes soft or sinks toward the floor.

Moisture also drives internal corrosion over time in parts you cannot see, including the ABS/stability control unit and the caliper bores. Replacing the fluid every 2 years is far cheaper than replacing those components.

Signs the Fluid Is Overdue

• Time: If you cannot document a flush in the last 2 years, assume it is due. This is the most reliable sign because moisture uptake is invisible.
• Soft or long pedal after hard use: A pedal that feels normal around town but goes soft after repeated hard stops points to fluid that is boiling.
• Dark fluid in the reservoir: Fresh DOT 4 LV is light amber. Dark fluid has been in service a long time, though color alone does not tell you the water content.
• Low reservoir level: The level drops slowly as pads wear, because the caliper pistons move out. A level that drops fast or sits below MIN points to a leak and needs inspection before driving. The manual warns that a level below MIN can impair braking.
• Brake warning light: Treat any brake warning in the instrument cluster as a stop-and-check item.

A shop can test moisture content or boiling point with a tester, but on this car the calendar is the rule. Audi's schedule does not say to change the fluid when a test fails; it says every 2 years.

How the Flush Is Done and What to Do at the Same Time

A brake fluid change on the S5 is a full flush and bleed: old fluid is pushed out of each caliper through the bleeder screws until clean fluid comes through, while the reservoir is kept topped up so no air is drawn in. Most shops use a pressure bleeder on the reservoir. Audi recommends the job be done by a competent technician with proper equipment, and there are good reasons for that. If air gets into the ABS/stability control hydraulic unit, clearing it can require a scan tool routine. For the exact bleeding sequence and bleeder screw torque, follow the factory repair information for your car.

Two practical tips if you do it yourself:

• Use fluid from a freshly opened, sealed bottle. An old opened bottle has been absorbing moisture on the shelf.
• Keep fluid off the paint. The manual warns brake fluid will corrode paint on contact. Cover the fender and wipe up spills immediately.

The best time to flush is when you are already doing brakes. Pushing caliper pistons back for new pads sends old fluid back toward the reservoir, so doing pads and a flush together means the new pads start with fresh fluid. Audi's schedule also calls for checking brake hoses and bleeder caps at each Standard Maintenance, so inspect the hoses for cracking or bulging while the wheels are off.

If your pads are near the end, we carry pads confirmed to fit the 2018-2019 S5:

• Hawk Performance Ceramic front brake pads for the 2018-2019 Audi S5 - a quiet, low-dust street compound.
• Hawk HPS 5.0 front brake pad set for the 2018-2019 Audi S5 - a performance street compound with more bite.
• Hawk HPS 5.0 rear brake pads for the 2018-2019 Audi S5 - to match the front set.

You can also browse all brake pads, brake rotors and replacement brake hoses if the inspection turns up anything else.

Frequently Asked Questions

What brake fluid does a 2018 or 2019 Audi S5 take?

Fluid that meets VW 501 14. If that is not available, the owner's manual allows a high-grade fluid meeting FMVSS 116 DOT 4, Class 6, which is a low-viscosity DOT 4, often labeled DOT 4 LV.

How often should I change the brake fluid on my S5?

Every 2 years, according to Audi's 2018 maintenance schedule, which applies that interval to all Audi vehicles with no mileage figure. Cars that see track days or heavy mountain driving benefit from changing it more often.

Can I use regular DOT 4 instead of DOT 4 LV?

Regular DOT 4 meets the federal boiling-point minimums, but it can be much thicker in the cold than the low-viscosity fluid Audi specifies for the ABS and stability-control system. Use a VW 501 14 or DOT 4 Class 6 fluid for a flush.

Can I use DOT 3 or DOT 5?

No. DOT 3 has lower boiling-point minimums than DOT 4 and does not meet the S5 specification, and DOT 5 is a silicone fluid of a different chemistry. Stick to a fluid whose bottle lists VW 501 14 or DOT 4 Class 6.

My S5 has low mileage. Do I still need a brake fluid change?

Yes. Brake fluid absorbs moisture over time whether the car is driven or not, which is why Audi's interval is based only on time.

Should I just top off the reservoir if it is low?

A slightly lower level is normal as pads wear. Topping off does not remove the water already in the fluid, and a level that drops quickly or falls below MIN means the system should be inspected for leaks before you drive.

Sources

1. 2018 Audi Maintenance Schedule - All Models (Audi of America, via NHTSA) - brake fluid change every 2 years for all vehicles; pad and hose check intervals
2. Audi B9 owner's manual - Brake fluid checking and filling - VW 501 14 requirement, DOT 4 Class 6 alternative, reservoir location, old-fluid and paint warnings
3. 49 CFR 571.116, FMVSS No. 116 Motor vehicle brake fluids (Cornell LII) - DOT 4 dry and wet boiling points, -40 C viscosity limit, container moisture warning
4. Pentosin DOT 4 LV product data sheet (CRP Automotive) - low-viscosity fluid specs, ISO 4925 Class 6, ESP/ABS suitability
5. Ravenol DOT 4 LV brake fluid - VW 501 14 recommendation, -40 C viscosity, not for mineral-oil systems