2005-2008 Subaru LGT Brake Fluid Type and Flush Interval

By Core Brake Parts Tech Team — Circleville, OH warehouse

The 2005-2008 Subaru Legacy GT takes FMVSS No. 116 DOT 3 or DOT 4 brake fluid from a sealed container, and Subaru's maintenance schedule calls for replacing it every 30,000 miles or 30 months, whichever comes first. If you live somewhere humid or mountainous, Subaru shortens that to every 15,000 miles or 15 months. The same fluid spec also fills the clutch reservoir on manual-transmission cars.

What Subaru Specifies for the LGT

Subaru's owner's manuals for the 2005 and 2008 Legacy both list the recommended brake fluid as FMVSS No. 116, fresh DOT 3 or DOT 4. FMVSS No. 116 is the federal motor vehicle safety standard that defines brake fluid grades; it is a standard, not a brand or part number. Any fluid labeled DOT 3 or DOT 4 has to meet it.

Subaru adds a few rules in the same section that matter more than most owners realize:

• Never mix brands. The manual says never to use different brands of brake fluid together.
• Do not mix DOT 3 and DOT 4. The 2008 Legacy manual goes further and says to avoid mixing DOT 3 and DOT 4 even when they are the same brand. Pick one and flush the whole system to it.
• Sealed container only. Brake fluid absorbs moisture from the air, and Subaru warns that absorbed moisture can cause a dangerous loss of braking performance. A half-used bottle that has sat open on a shelf is not "fresh."
• Protect paint and rubber. The manual warns that the alcohol in brake fluid can damage painted surfaces and rubber parts, and that fluid on the exhaust can smoke or catch fire. Wipe spills right away.

Manual-transmission LGTs have a separate clutch reservoir. Subaru lists the same FMVSS No. 116 DOT 3 or DOT 4 fluid for it, so treat it as part of the same service.

DOT 3 vs DOT 4: What the Numbers Mean

The difference between grades is boiling point. FMVSS No. 116 sets two minimums for each grade: a dry boiling point for new fluid, and a wet boiling point measured after the fluid has absorbed water. The wet number is the one your car lives with after a couple of years.

Two things stand out. First, a DOT 3 fluid that has soaked up water can boil at a far lower temperature than when it was new, which is exactly why Subaru puts brake fluid on a fixed replacement schedule instead of "check and top off." Second, DOT 5 has higher numbers on paper, but it is a silicone-based fluid that the standard requires to be dyed purple, and Subaru does not list it for this car. Do not put it in.

For a daily-driven LGT, either DOT 3 or DOT 4 meets the factory spec. DOT 4 gives you more margin before the fluid boils, which is worth having on a turbocharged car that sees mountain descents, spirited driving or autocross.

The Flush Interval, Straight From Subaru's Schedule

Subaru did not print the maintenance schedule in the owner's manual; the manual sends you to the separate Warranty and Maintenance Booklet. The 2005 and 2008 booklets both show brake fluid as a Replace item at 30,000, 60,000, 90,000 and 120,000 miles, with matching months columns, whichever occurs first.

The humidity and mountain rule is easy to miss because it is a footnote to the schedule. Humid air puts more water into the fluid, and long downhill grades put more heat into it. Both shorten the time before the boiling point drops too far. On a car this age the months column usually comes up before the miles column does, so go by the calendar if you are not sure when it was last done.

Between flushes, the owner's manual says to check the level monthly on the outside of the reservoir. If it is below MIN, add the recommended fluid up to MAX.

Symptoms That Your Fluid Is Overdue

• Soft or sinking pedal after hard use. Water in the fluid turns to vapor when the brakes get hot, and vapor compresses. A pedal that goes long after a canyon run or a track session is the classic sign.
• Dark fluid in the reservoir. Fresh DOT 3 and DOT 4 are clear to amber. Color alone is not a test, but dark fluid on a car with no service record is a good reason to flush.
• Brake warning light with the parking brake released. On the LGT the brake system warning light doubles as a fluid level warning. Subaru says it comes on when the level drops near MIN, and that this can mean a leak or worn brake pads. If the level is below MIN, Subaru says do not drive the car.
• Frequent topping off. Subaru notes that a car that needs frequent refilling may have a leak. The level drops slowly as pads wear, and quickly only when something is leaking.

If the brake system warning light and the ABS light come on together, Subaru's manual points to a possible fault in the Electronic Brake Force Distribution system. That is a different problem from low fluid and should be inspected.

Doing the Flush on a Legacy GT

The LGT has four-wheel disc brakes with ABS and a vacuum brake booster that runs off engine manifold vacuum. A standard pressure or two-person bleed moves fresh fluid through each wheel circuit; the goal is to push enough new fluid through that the old fluid is fully displaced.

1. Buy enough sealed fluid of one brand and one grade to flush the whole system, plus the clutch circuit on a manual car. Do not reuse fluid.
2. Remove old fluid from the reservoir and refill with fresh fluid. Keep dirt out of the reservoir, as the manual warns.
3. Bleed each caliper until clean fluid comes out, following the bleed sequence and procedure in the factory service manual. Never let the reservoir run dry, or you will pull air into the system.
4. Tighten the bleeder screws to the value in the factory service manual; they are small and strip easily.
5. Top the reservoir to MAX and check the pedal before moving the car. Subaru's manual describes a simple booster check: with the engine off, pump the pedal several times; then hold it down and start the engine, and the pedal should move slightly toward the floor.

A two-person bleed with a clear hose on the bleeder is enough for most DIYers. Wear eye protection; Subaru warns that brake fluid is harmful to eyes.

What to Do at the Same Time

A flush is the natural time to look at the rest of the brake system. Subaru's schedule has you inspect the disc brake pads and discs and the brake lines at regular intervals, so check pad thickness and rotor condition while the wheels are off. Subaru notes the right front and right rear pads carry audible wear indicators that scrape when the pads are near the service limit.

If your pads are due, we carry several front pad compounds for the 2005-2008 Legacy GT, including the Hawk HPS street front pads for the Legacy GT, the lower-dust Hawk Ceramic Street front pads, and the more aggressive Hawk HP Plus front pad set for owners who drive hard. For dedicated track use there is the Hawk DTC-60 race pad; Hawk rates that compound for 400 to 1,600 F and lists motorsport applications, so it belongs on a track car, and a car driven that hard deserves fresh DOT 4. Out back, the DBA T2 slotted rear rotor for the Legacy GT fits these years. Browse our brake hoses and brake lines if the rubber hoses are cracked or swollen.

Frequently Asked Questions

Can I use DOT 4 in my 2005-2008 Legacy GT?

Yes. Subaru's owner's manual lists FMVSS No. 116 DOT 3 or DOT 4. Just do not mix the two in the system; flush completely when you switch.

How often should I change brake fluid on a Subaru LGT?

Every 30,000 miles or 30 months, whichever comes first, under Subaru's schedule. In high humidity or mountainous areas, Subaru says every 15,000 miles or 15 months.

Can I use DOT 5 silicone fluid?

No. Subaru specifies DOT 3 or DOT 4 only. DOT 5 is a silicone-based fluid and is not on Subaru's list for this car.

Why is my brake warning light on when the parking brake is off?

On the Legacy GT that light also warns of low brake fluid. Check the reservoir. If the level is below MIN, Subaru says not to drive the car, because it can mean a leak or worn pads.

Does the clutch use the same fluid?

Yes. On manual-transmission cars, Subaru lists FMVSS No. 116 DOT 3 or DOT 4 brake fluid for the clutch reservoir too.

Sources

1. Subaru 2005 Legacy Owner's Manual - recommended brake and clutch fluid (FMVSS No. 116 DOT 3 or 4), monthly level check, vacuum brake booster, warning light, pad wear indicators
2. Subaru 2008 Legacy Owner's Manual - DOT 3 or 4 spec, do not mix DOT 3 and DOT 4, moisture and eye-safety warnings
3. Subaru 2005 Warranty and Maintenance Booklet - brake fluid replacement interval and the 15,000-mile/15-month humid or mountainous rule
4. Subaru 2008 Warranty and Maintenance Booklet - same brake fluid interval and brake inspection items for the 2008 model year
5. 49 CFR 571.116, FMVSS No. 116 (Cornell LII) - DOT 3, DOT 4 and DOT 5 dry and wet boiling point minimums, DOT 5 purple color
6. Hawk Performance DTC-60 - compound temperature range and motorsport applications