2001-2007 Acura RSX Brake Fluid Type and Flush Interval

By Core Brake Parts Tech Team — Circleville, OH warehouse

The Acura RSX calls for DOT 3 brake fluid. Acura's owner's manual names its own Heavy Duty Brake Fluid DOT 3, allows DOT 3 or DOT 4 from a sealed container as a temporary substitute, and schedules a brake fluid replacement every 3 years regardless of mileage. On manual-transmission cars, the hydraulic clutch uses the same fluid, so it belongs in the same service.

What Fluid the RSX Uses and Where It Goes

The RSX owner's manual is plain about this. The recommended fluid is Acura Heavy Duty Brake Fluid DOT 3. If that is not available, the manual allows DOT 3 or DOT 4 from a sealed container as a temporary replacement, and it warns that non-Acura fluid can cause corrosion and shorten the life of the system, so the system should be flushed and refilled with the Acura DOT 3 fluid as soon as possible. It also states that fluid marked DOT 5 is not compatible with the RSX braking system and can cause extensive damage.

Under the hood of a manual-transmission car you will find two reservoirs with gray caps: one for the brakes and one for the hydraulic clutch. Automatic cars only have the brake reservoir. Both reservoirs have MIN and MAX marks on the side, and the manual says to use the same fluid in the clutch that is specified for the brakes.

Why the Interval Is 3 Years, Not a Mileage Number

The 3-year replacement appears on both the Normal and the Severe Conditions maintenance schedules in the RSX manual, and it is listed as "independent of mileage." That is because the enemy is time and humidity, not miles. Glycol-based fluids such as DOT 3 and DOT 4 are hygroscopic: they pull water from the surrounding air whether the car is driven daily or sits in a garage.

Water lowers the fluid's boiling point, and the minimum standards show how much. DOT 3 must boil no lower than 401 degrees F when fresh (dry) and no lower than 284 degrees F in the "wet" test, which is run on fluid carrying about 3.7 percent water. DOT 4 minimums are 446 degrees F dry and 311 degrees F wet. When fluid in a hot caliper boils, it forms vapor bubbles that compress, and the pedal goes soft or sinks. Water in the fluid also promotes internal corrosion in calipers, the master cylinder and the ABS unit, which is the expensive part to replace.

DOT 3 or DOT 4 in an RSX?

For a street-driven RSX, a fresh DOT 3 flush on the 3-year schedule is exactly what the car was designed around. DOT 3, DOT 4 and DOT 5.1 are all glycol-based and can be mixed without damaging the system, so topping up with DOT 4 in a pinch will not hurt anything. One trade-off worth knowing: once water gets into DOT 4, its boiling point typically falls off faster than a typical DOT 3's, so a higher-rated fluid does not buy you a longer interval. Keep the 3-year clock either way.

If you track the car or autocross it, the rules change. Track heat is what boils fluid, and a performance setup deserves a higher-temperature racing fluid and a much shorter change interval. Wilwood, for example, instructs owners of its Forged Dynalite front big brake kit for the 2002-2006 RSX to fill and bleed with its high-temperature racing fluid, to flush the old fluid completely to prevent contamination, and it states that silicone DOT 5 is not recommended for racing or performance driving. Whatever you choose, do not put DOT 5 in an RSX.

Symptoms That Say the Fluid or System Needs Attention

• Brake system indicator on while driving. The manual says this usually means the fluid level in the reservoir is low. Press the pedal lightly to see whether it feels normal, and check the level at your next stop.
• Level at or below MIN. Brake fluid is not consumed. A dropping level points to worn pads (caliper pistons extend and draw fluid down) or a leak, and the manual says to have the system inspected for leaks or worn pads.
• Soft or sinking pedal, especially after hard stops. This can be boiled or wet fluid, air in the lines or a hydraulic fault.
• Pedal travels much farther and stops take more effort. The RSX has two hydraulic circuits split diagonally, left-front with right-rear and so on. If one circuit fails you still have braking at two wheels, but the manual says to have the car towed and repaired.
• Dark fluid. Fresh fluid is clear to light amber. Dark fluid is old, though color alone does not tell you the water content.
• Soft clutch pedal or a clutch that will not fully disengage (manual cars). The clutch shares the same fluid and the same moisture problem, and the manual says a low clutch reservoir can indicate a leak in that system.

Doing the Flush, and What to Check While You Are There

The RSX uses disc brakes at all four wheels, a power assist and ABS. A proper fluid replacement pushes new fluid through every caliper until clean fluid comes out of each bleeder, rather than just emptying the reservoir. For the factory system, follow the bleed sequence and any ABS procedure in the factory service manual. On an aftermarket caliper setup, follow that maker's instructions: Wilwood's RSX kit sheet says to start with the caliper farthest from the master cylinder and, on its calipers, bleed the outboard bleed screw first and then the inboard. Tighten bleeders to the value in the factory service manual or the caliper maker's instructions, and never let the reservoir run dry during the job or you will pull air into the system.

On a manual car, bleed the clutch slave cylinder with the same fluid during the same visit. Use fluid from a freshly opened, sealed container, because an opened bottle on the shelf keeps absorbing moisture.

A flush is a good time to inspect the rest of the hydraulic system, which the RSX maintenance schedule already asks for: front and rear brakes, parking brake adjustment, and the brake hoses and lines including the ABS lines. Cracked, swollen or chafed rubber hoses should be replaced, and replacement brake hoses and brake lines are worth doing with the flush since you are bleeding the system anyway. If a caliper piston is seized or a caliper is leaking, see our brake calipers. A pedal that slowly sinks under steady pressure with no external leak points toward the master cylinder.

Pads and Rotors That Fit the RSX

If the level has dropped because the pads are worn, the RSX will usually tell you: its pad wear indicators make a metallic screeching sound when you apply the brakes, and if the pads are not replaced they will screech all the time. The base car and the Type-S take different front pads, so match by trim:

• Base (non-S) front: Hawk HPS street pads HB418F.646, or Hawk HP Plus HB418N.646 for harder driving.
• Type-S front: Hawk HPS 5.0 HB361B.622 for the street, or Hawk DTC-60 race pads HB361G.622 for track use only.
• Front rotors: EBC BSD V-slot front rotor pair BSD7126.

Race compounds such as DTC-60 are not street pads; they are built for track temperatures. Confirm the part against your trim before ordering, or browse all brake pads and brake rotors.

How hard is the job? A fluid flush is a moderate DIY job with a helper or a one-person bleeder, and most of the effort is being methodical so no air gets in. If the ABS indicator stays on afterward, or the pedal will not firm up after a careful bleed, have the car checked by a shop.

Frequently Asked Questions

What type of brake fluid does an Acura RSX take?

DOT 3. The owner's manual specifies Acura Heavy Duty Brake Fluid DOT 3, with DOT 3 or DOT 4 from a sealed container allowed as a temporary replacement.

How often should RSX brake fluid be changed?

Every 3 years, independent of mileage. That interval appears on both the Normal and Severe Conditions maintenance schedules.

Can I use DOT 4 in my RSX?

As a temporary replacement, yes, per the manual. DOT 4 mixes safely with DOT 3, but the manual still recommends flushing back to the specified DOT 3 fluid as soon as possible. Never use DOT 5.

Does the RSX clutch use brake fluid?

Yes, on manual-transmission cars. The manual says to use the same fluid specified for the brake system in the clutch reservoir, so flush both together.

Why is my RSX brake fluid level going down?

Usually worn pads, since the caliper pistons extend as the pads wear and draw fluid from the reservoir. If the pads are fine, look for a leak at the calipers, hoses, lines or master cylinder. The manual says a level at or below MIN needs a brake inspection.

Do I need to flush the fluid when I install a big brake kit?

Yes. New calipers must be filled and bled, and Wilwood's RSX kit instructions call for flushing the old fluid completely to avoid contamination.

Sources

1. 2006 Acura RSX Owner's Manual - DOT 3 specification, DOT 5 warning, 3-year replacement interval, MIN/MAX level checks, clutch fluid, diagonal dual circuits, four-wheel discs with ABS, pad wear indicators, brake system indicator
2. 2003 Acura RSX Owner's Manual, Brake and Clutch Fluid - DOT 3 specification and same fluid for the clutch on earlier model years
3. Wilwood assembly instructions, 2002-2006 Acura RSX front kit - full flush with new calipers, high-temperature fluid for performance use, DOT 5 not recommended, bleed order
4. Tilton Engineering: Brake Fluid - DOT 3 and DOT 4 dry and wet boiling points, 3.7 percent water wet test, hygroscopic glycol fluids, DOT 3/4/5.1 mixing
5. TotalEnergies: Brake fluid types - wet DOT 4 losing boiling point faster than DOT 3, DOT 5 non-hygroscopic behavior