2013-2016 Mercedes-Benz C300 Brake Fluid Type and Flush Interval

By Core Brake Parts Tech Team — Circleville, OH warehouse

Every 2013-2016 Mercedes-Benz C300 uses brake fluid approved to Mercedes-Benz specification MB 331.0, a DOT 4 class glycol fluid, and Mercedes-Benz USA schedules a brake fluid exchange with every Service B, which comes up about every 20,000 miles or 2 years. That applies to both the 2013-2014 W204 sedan with the 3.5L V6 and the 2015-2016 W205 with the 2.0L turbo. If you are overdue, plan the flush before your next hard stop, not after.

What Mercedes-Benz specifies for the C300

Both the 2013 C-Class Operator's Manual (W204) and the 2015 C-Class Operator's Manual (W205) use the same wording: only use brake fluid approved by Mercedes-Benz according to MB Approval 331.0. The manuals do not print a DOT number on that page; they point you to the Mercedes-Benz service products list, and 331.0 is the approval that covers brake fluid for Mercedes passenger cars. Fluids sold against that approval are labeled DOT 4 Plus or DOT 4 with the 331.0 approval printed on the bottle.

The 2015 manual adds a second line worth reading: Mercedes-Benz recommends only brake fluid specially approved for your vehicle, or fluid of an equivalent quality standard, because fluid that is not of equivalent quality could affect the car's operating safety. In plain terms, a generic bottle that only says DOT 3 is the wrong choice for this car.

Why the 2-year flush matters: moisture and boiling point

Mercedes puts the reason right in the owner's manual warning: brake fluid constantly absorbs moisture from the air, which lowers its boiling point. If the boiling point drops too far, vapor pockets can form in the system under hard braking and braking efficiency falls off. Vapor compresses, fluid does not, so the pedal goes soft and travels further.

The federal brake fluid standard, FMVSS No. 116, shows how big that drop can be. It sets separate minimums for fresh (dry) fluid and for fluid that has absorbed water (wet):

A DOT 4 fluid is allowed to lose well over 100 degrees F of boiling point once it is wet. Because the fluid picks up water continuously and you cannot see it happen, Mercedes uses a time-based interval instead of waiting for a symptom. A C300 that sits in a garage most of the year still needs the flush on the calendar, even if the odometer barely moved.

Viscosity matters too. The C300 has ABS and ESP, which move fluid through small valves in the hydraulic unit very quickly. Brake fluid makers formulate low-viscosity DOT 4 fluids specifically so ESP and ABS can react faster. Old, water-laden fluid also carries corrosion into those valves and into the calipers.

Symptoms your C300 brake fluid needs attention

• Service B is due or overdue. The maintenance display counts it down. If the car has missed a B service, assume the fluid is old.
• Soft or long pedal after repeated hard stops, such as a long downhill grade, that firms up again after the brakes cool. That is the classic sign of fluid boiling.
• Dark fluid in the reservoir. Fresh fluid is clear to light amber. Dark fluid is old, though color alone does not tell you the water content; a shop moisture or boiling-point test does.
• "Check Brake Fluid Level" message with the red brake warning lamp and a warning tone. This one is not a flush reminder. See the next section.

Low brake fluid warning: do not just top it off

The 2015 C-Class manual is blunt about the Check Brake Fluid Level message: pull over safely, do not continue driving, secure the car, and consult a qualified workshop. It also says not to add brake fluid, because that does not correct the malfunction.

The manual explains why the level drops: brake pad wear or leaking brake lines. As pads wear, the caliper pistons move out and more fluid sits in the calipers, so the reservoir level falls slowly. A sudden drop, or a low level with pads that still have plenty of lining, points to a leak at a line, hose, caliper or master cylinder. Topping off hides the evidence and does nothing about the leak.

What to check, in order:

1. Pad thickness on all four corners. The C300 also has a Check Brake Pad Wear message tied to its wear sensors.
2. Wet spots at each caliper, at the flexible hoses behind each wheel, and along the hard lines.
3. The master cylinder and the area where it meets the booster.

If pads are the cause, replace pads and, in most cases, rotors, then bring the level back to the mark. Parts for a leak fix are in our brake hoses, brake lines and master cylinder collections.

How a C300 brake fluid flush is done

Mercedes says in the owner's manual to have brake fluid replaced at a qualified specialist workshop and the replacement confirmed in the Maintenance Booklet. That is sensible advice for most owners, and there is a practical reason: bleeding a car with ABS and ESP is more involved than on an older car.

• Use only 331.0 approved fluid from a sealed bottle. An opened bottle starts absorbing moisture, so do not use one that has been sitting on a shelf.
• Pressure bleeding is the usual method. A pressure bleeder on the reservoir pushes new fluid through each caliper in turn until clean fluid comes out. Follow the bleed sequence and pressure in the factory service information for your chassis.
• The ABS/ESP hydraulic unit may need to be cycled with a scan tool to purge old fluid or air from its internal circuits, especially if the system was run low or opened. A routine exchange at the calipers usually does not require it, but a repair that let air into the system can.
• Do not let the reservoir run dry during the job. Air drawn into the master cylinder or hydraulic unit turns a simple flush into a much longer bleed.
• Finish by testing pedal feel with the engine running and a low-speed stop before driving in traffic.

Brake fluid damages paint, so cover the fender and wipe up spills immediately with water.

What to do at the same time

A flush is a good time to look at the rest of the brake system, since the wheels are already off.

• Pads and rotors. Mercedes recommends replacing all brake disks and pads on an axle at the same time and using disks and pads approved by Mercedes-Benz or of an equivalent quality standard. For the 2013-2014 W204 C300, we carry the EBC Ultimax OE-style front rotor set RK1531. For the 2015-2016 W205 with the AMG Sport Package, there are the EBC Redstuff ceramic low-dust rear pads DP32270C for daily driving and the EBC Yellowstuff street and track rear pads DP42270R for harder use. The 2016 W205 also fits the DBA Street Series T2 slotted rear rotor DBA3357HOES. Always confirm fitment by brake package, since C300 brake sizes vary.
• Pad wear sensors. Most shops replace the wear sensor on any axle where it has been triggered.
• Hoses. Look for cracking or bulging on the flexible hoses. Browse brake pads and brake rotors for other C300 configurations.

Frequently Asked Questions

Can I use regular DOT 4 brake fluid in my C300?

Mercedes-Benz specifies fluid approved to MB 331.0, or fluid of an equivalent quality standard. The safest choice is a bottle that lists the 331.0 approval. A generic DOT 4 without that approval is not confirmed to meet what Mercedes requires for this ABS and ESP system.

Can I use DOT 3 in a Mercedes C300?

No. DOT 3 has lower minimum boiling points than DOT 4 under the federal standard and does not meet the MB 331.0 approval the C300 manuals call for.

How often should a 2013-2016 C300 get a brake fluid flush?

With every Service B, which Mercedes-Benz USA schedules about every 20,000 miles or 2 years. Go by time even on a low-mileage car, because the fluid absorbs moisture whether the car is driven or not.

My C300 says Check Brake Fluid Level. Can I just add fluid?

No. The owner's manual says to stop driving, not to add fluid, and to have the car checked, because a low level comes from worn pads or a leak. Find the cause first.

Is a brake fluid flush the same as bleeding the brakes?

Both push fluid out through the bleeders. A flush replaces all the old fluid on a schedule; bleeding removes air after a repair. On the C300, either job may call for a scan tool to cycle the ABS/ESP unit if air got into it.

Sources

1. Mercedes-Benz USA, 2015 C-Class Operator's Manual - MB 331.0 approval, moisture warning, Check Brake Fluid Level instructions, pad and disk recommendations
2. Mercedes-Benz USA, 2013 C-Class Operator's Manual - MB 331.0 approval for the W204
3. Mercedes-Benz USA, Service and Maintenance - brake fluid exchange in Service B, 20,000 miles or 2 years
4. 49 CFR 571.116, FMVSS No. 116 Motor Vehicle Brake Fluids - DOT 3 and DOT 4 dry and wet boiling points and viscosity limits
5. ATE brake fluids - low-viscosity DOT 4 fluids formulated for ESP and ABS response