2017 BMW M240 Brake Fluid Type and Flush Interval

By Core Brake Parts Tech Team — Circleville, OH warehouse

The 2017 BMW M240i uses DOT 4 Low Viscosity (DOT 4 LV) brake fluid, the glycol-based spec BMW uses across its DSC-equipped cars. BMW treats the fluid change as a calendar item, not a mileage item: BMW dealers state the factory recommendation is a brake fluid replacement every two years, whether the car is driven daily or sits in a garage. If you track the car, change it far more often than that.

Below is what DOT 4 LV actually is, why the M240i needs the low viscosity version, how to tell your fluid is overdue, and what a correct BMW flush involves.

Which Brake Fluid the 2017 M240i Takes

The F22 M240i coupe is filled with DOT 4 Low Viscosity fluid. BMW specialist BimmerWorld lists DOT 4 Low Viscosity as the street fluid for 2006 and newer BMWs, with DOT 5.1 and the newer Class 6 and Class 7 fluids also acceptable because they meet the same low-viscosity requirement. The reservoir cap is marked with the fluid spec as well, so check it before you buy.

What you should not use: plain DOT 3, or DOT 5 silicone fluid. DOT 3 is glycol-based, but it has lower boiling points and is not the viscosity BMW specifies. DOT 5 silicone does not mix with glycol fluids and should never go into this system.

The DOT 3 and DOT 4 figures are the minimums written into federal standard FMVSS 116 (49 CFR 571.116). Any fluid sold as DOT 4 must meet them; DOT 4 LV goes beyond them on boiling point while staying much thinner when cold.

Why the M240i Needs Low Viscosity Fluid

The M240i relies on BMW's Dynamic Stability Control (DSC) and ABS hydraulic unit to modulate each wheel's brake pressure many times per second. As BimmerWorld explains, the DSC pump moves fluid at very high pressure in a very short time, and fluid that is too thick, especially in cold weather, slows that response. BMW moved to a thinner fluid for exactly this reason. Standard-viscosity DOT 4 in a street M240i will stop the car, but it is not what the stability system was designed around, particularly on a cold morning.

Track-focused owners sometimes run a normal-viscosity racing fluid for its higher boiling point. That is a trade-off for track use, not a street upgrade, and it comes with even more frequent fluid changes.

Why BMW Uses a Time-Based Flush Interval

All glycol-based brake fluids (DOT 3, DOT 4, DOT 5.1) are hygroscopic: they pull moisture from the air through hoses, seals and the reservoir vent. The federal labeling rule for brake fluid containers makes the point bluntly, telling users to keep the fluid clean and dry and the container tightly closed to prevent absorption of moisture.

Moisture lowers the boiling point. Look at the gap in the table above between the dry and wet boiling points: that drop is what water does. When fluid boils in a hot caliper, it forms vapor bubbles that compress, and the pedal goes soft or sinks. Mporium BMW notes that this moisture pickup happens even if the car sits unused, which is why BMW schedules the service by calendar rather than miles. BMW dealers put that at every two years. United BMW adds that glycol fluids should be changed every one to two years under non-racing conditions and recommends checking the level at every oil change or at least once a year.

Your M240i's Condition Based Service (CBS) display tracks the brake fluid due date for you. When it shows brake fluid service due, it is counting time since the last reset, not measuring the fluid.

Signs the Fluid Is Overdue

• Dark fluid in the reservoir. Fresh fluid is clear with a slight yellow tint. Brown or tea-colored fluid has picked up moisture and contamination.
• Soft or long pedal after hard stops. A pedal that fades on a long descent or after a spirited drive and then recovers when cool is the classic sign of moisture-laden fluid boiling.
• Brake fluid service reminder in the CBS display. This is the time-based reminder, but it means the scheduled interval has passed.
• Low level warning. A falling level is usually worn pads (the caliper pistons sit further out), but it can also be a leak. Inspect before topping up.

A low reservoir alone does not mean the fluid is bad. As pads wear, the level drops. If you replace pads with a set like our EBC Bluestuff NDX front brake pads for the M240i coupe, the level rises again as the pistons are pushed back, so do not overfill before a pad job.

How a Correct BMW Brake Fluid Flush Is Done

A brake fluid flush on the M240i is more than opening four bleeders. Mporium BMW describes the factory-approved process:

1. Fresh fluid is supplied from sealed equipment, so it has not been sitting open absorbing moisture.
2. The equipment pressurizes the reservoir and pushes fluid through the closed system.
3. Old fluid is collected at each caliper bleeder until clean fluid appears.
4. The DSC/ABS pump is activated at each corner with a diagnostic tool to purge old fluid trapped inside the hydraulic unit.
5. The reservoir is topped to the correct level and fault codes are checked.
6. The CBS brake fluid reminder is reset.

Step 4 is the one DIY jobs usually skip. A pressure bleeder and a basic bleed will replace most of the fluid, but old fluid inside the DSC unit stays there unless the pump is cycled with a capable scan tool. Step 6 matters too: without a reset, the reminder stays on.

Difficulty: moderate. With a pressure bleeder, a scan tool that can run the BMW DSC bleed routine and fresh sealed DOT 4 LV, a careful owner can do it in the driveway. Without the scan tool, the result is a partial flush.

What to Replace at the Same Time

A fluid flush is a good moment to look at the rest of the hydraulic system:

• Pads and rotors. Check pad thickness and rotor condition while the wheels are off. Browse brake pads and brake rotors.
• Hoses. Rubber flex hoses age and crack. Look for bulging or cracking at each corner; replacements are under brake hoses, and braided options under brake lines.
• Bleeder screws. Seized or rounded bleeders are the most common reason a flush turns into a caliper job. Free them gently and replace any that are damaged.

Frequently Asked Questions

Can I use regular DOT 4 in my 2017 M240i?

It will stop the car, but BMW specifies DOT 4 Low Viscosity for DSC-equipped cars because the thinner fluid lets the stability and ABS system respond quickly, especially in cold weather. Use DOT 4 LV, or a fluid that meets the same low-viscosity requirement, for street driving.

How often should I flush the brake fluid on an M240i?

BMW dealers state the recommendation is every two years regardless of mileage. If you do track days, change it before each event, since heat and absorbed moisture together lower the boiling point fast.

Is DOT 5.1 compatible with the M240i?

BimmerWorld lists DOT 5.1 as an acceptable street fluid for 2006 and newer BMWs. DOT 5.1 is glycol-based. Do not confuse it with DOT 5, which is silicone and must never be used in this system.

Why is my brake fluid service due when I barely drive the car?

Brake fluid absorbs moisture from the air even when the car is parked. That is why the CBS reminder is based on time, not miles.

Do I need a scan tool to flush the fluid?

To do it the factory way, yes. The DSC/ABS unit needs to be cycled at each corner to purge old fluid from inside the hydraulic unit, and the CBS reminder needs a reset. A basic bleed without a scan tool replaces most, but not all, of the fluid.

Sources

1. BimmerWorld - BMW Brake Fluid Types - DOT 4 LV as the 2006+ BMW street fluid, its boiling points, DSC viscosity reasoning, DOT 5.1 acceptable
2. 49 CFR 571.116 (FMVSS 116), Cornell LII - DOT 3 and DOT 4 minimum boiling points, viscosity limits, moisture warning
3. BMW of Coconut Creek - BMW Ultimate Care Services - BMW recommends brake fluid replacement every two years
4. Mporium BMW - What Is a Brake Fluid Service - calendar-based interval, hygroscopic fluid, factory flush steps including DSC purge
5. United BMW - How to Check Brake Fluid - checking the level, fresh fluid color, glycol fluid change guidance