2004-2007 Subaru Impreza Brake Fluid Type and Flush Interval

By Core Brake Parts Tech Team — Circleville, OH warehouse

The 2004-2007 Subaru Impreza takes fresh DOT 3 or DOT 4 brake fluid that meets FMVSS No. 116, and Subaru's owner's manual tells you not to mix DOT 3 with DOT 4 or mix brands. Plan on a full flush at the 30,000-mile service and again at 60,000 miles. Because the fluid soaks up moisture as it ages, a car that sits a lot needs it done on time as well as miles.

What brake fluid the 2004-2007 Impreza uses

The 2006 Impreza owner's manual lists the recommended brake fluid as "FMVSS No. 116, fresh DOT 3 or 4 brake fluid." The 2007 manual uses the same spec, so the answer holds across the second-generation Impreza years this guide covers, from the base 2.5i to the WRX and STI. FMVSS No. 116 is the federal standard every DOT-rated fluid sold in the US has to meet, so any sealed bottle labeled DOT 3 or DOT 4 is the right family of fluid.

Subaru adds three rules that matter more than the brand you buy:

• Do not mix brands. The manual says never to use different brands of brake fluid together.
• Do not mix DOT 3 and DOT 4. The manual says to avoid mixing them even when they are the same brand. If you want to switch grades, do a full flush rather than topping off.
• Only use fluid from a sealed container. An opened bottle that has been sitting on a shelf has already been pulling moisture from the air.

On manual-transmission cars the clutch hydraulic system uses the same fluid. The manual lists the recommended clutch fluid as FMVSS No. 116 fresh DOT 3 or 4 brake fluid, with the same warning about not mixing DOT 3 and DOT 4. If you are flushing the brakes on a manual-transmission car, it makes sense to flush the clutch circuit at the same visit.

DOT 3 vs DOT 4 for your Impreza

Both grades are glycol-based and both are approved. The difference is heat tolerance. FMVSS No. 116 sets these minimum boiling points:

The "wet" number is the minimum the fluid must still meet after it has absorbed moisture, and it is much lower than the dry number. That gap is why old fluid matters. For a daily-driven 2.5i or Outback Sport, DOT 3 does the job. For a WRX or STI that sees mountain roads, hard canyon driving or track days, DOT 4 gives more margin before the fluid boils and the pedal goes soft. Pick one and stay with it at every top-off.

Do not use DOT 5. It is silicone-based, it is not in Subaru's recommendation, and it should not be mixed with the glycol fluid already in the system.

Flush interval: when to change it

The owner's manual does not print the schedule itself. It states that scheduled maintenance items are shown in the separate Warranty and Maintenance Booklet that came with the car, so that booklet is the final word for your VIN. Published schedules for the 2006 Impreza put brake fluid replacement at the 30,000-mile service and again at 60,000 miles, which works out to roughly every 30,000 miles from there.

Mileage is only half of it. Subaru's manual warns that brake fluid absorbs moisture from the air and that absorbed moisture can cause a dangerous loss of braking performance. That happens whether the car is driven or parked. On a 2004-2007 Impreza that only covers a few thousand miles a year, do not wait for the odometer; check the booklet's time interval and go by whichever comes first. If you have no idea when the fluid was last changed on a used car, flush it now and start the clock.

Signs the fluid is overdue:

• Fluid in the reservoir has turned from clear amber to dark brown.
• The pedal feels softer after a long downhill or a few hard stops, then firms up once the brakes cool.
• There is no service record of a flush in the last 30,000 miles.

How to check the level and top off correctly

Subaru says to check the brake fluid level monthly from the outside of the reservoir, which is marked MAX and MIN. If it is below MIN, add the recommended fluid up to MAX. Keep dirt out of the reservoir when the cap is off.

A slow drop in level is normal as the pads wear, because the caliper pistons move out and the calipers hold more fluid. A level that needs frequent refilling is not normal. Subaru's manual says frequent refilling may mean a leak and that the car should be checked. Look at each wheel for wet spots on the inside of the tire, the caliper and the rubber hoses, and look under the master cylinder where it meets the brake booster.

Two handling cautions from the manual are worth repeating: brake fluid can damage paint and rubber, so wipe up any spill right away, and if it lands on the exhaust it can smoke or catch fire.

Doing the flush and what to replace at the same time

A flush means pushing new fluid through each wheel until clean fluid comes out of every bleeder, not just topping up the reservoir. The basics:

1. Buy enough sealed fluid of one grade and one brand for the whole job, plus some extra.
2. Remove old fluid from the reservoir and refill with new, never letting it drop below MIN during the job.
3. Bleed each wheel in the order given in the factory service manual until the fluid runs clear with no bubbles.
4. Tighten the bleeder screws to the factory service manual value, top off to MAX, and confirm a firm pedal before driving.
5. Road test at low speed first.

On a car this age, the flush is a good time to look at the rest of the hydraulic system. Cracked or swollen rubber lines should be replaced with new brake hoses, and a bleeder screw that will not break loose often means a caliper is due from our brake calipers range. If the pedal sinks slowly while you hold it at a stop, and there is no external leak, the master cylinder may be bypassing internally. With the wheels off, measure the pads and rotors too. Our brake pads and brake rotors collections are a good starting point for a full brake job while the system is already open.

Difficulty: a two-person bleed or a one-person pressure-bleeder job, and manageable for anyone who has done their own pads before. If the pedal is soft or sinks afterward, do not drive the car until it is fixed.

Frequently Asked Questions

Can I use DOT 4 in a 2005 Impreza that came with DOT 3?

Yes. Subaru approves both. The manual says to avoid mixing DOT 3 and DOT 4, so switch grades with a complete flush rather than topping off with the other type.

How often should I flush brake fluid on a 2004-2007 Impreza?

Published schedules put it at 30,000 and 60,000 miles. Your Warranty and Maintenance Booklet also sets a time limit, and low-mileage cars should follow the time interval because the fluid absorbs moisture even when parked.

Is the WRX or STI brake fluid different from the 2.5i?

The owner's manual gives one recommendation for the line: FMVSS No. 116 fresh DOT 3 or DOT 4. Many WRX and STI owners choose DOT 4 for its higher boiling point under hard use.

Does the clutch use the same fluid?

Yes. On manual-transmission models the recommended clutch fluid is FMVSS No. 116 fresh DOT 3 or 4 brake fluid, with the same do-not-mix warning.

Why is my brake fluid level dropping?

A gradual drop tracks pad wear and is normal. If you have to refill it often, Subaru says there may be a leak; inspect the hoses, calipers and master cylinder before driving further.

Sources

1. 2006 Subaru Impreza Owner's Manual, page 11-25 (Brake fluid) - FMVSS No. 116 DOT 3 or 4 spec, no mixing brands or grades, moisture warning, monthly level check
2. 2006 Subaru Impreza Owner's Manual (Clutch fluid, MT vehicles) - clutch uses the same DOT 3 or 4 fluid
3. 2006 Subaru Impreza Owner's Manual, page 11-3 (Maintenance schedule) - schedule is in the Warranty and Maintenance Booklet
4. 2007 Subaru Impreza Owner's Manual (Brake fluid) - same FMVSS No. 116 DOT 3 or DOT 4 recommendation for 2007
5. 49 CFR 571.116, FMVSS No. 116 Motor vehicle brake fluids - DOT 3 and DOT 4 minimum dry and wet boiling points
6. Kelley Blue Book, 2006 Subaru Impreza maintenance schedule - brake fluid change at 30,000 and 60,000 miles