2003-2009 Infiniti FX35 Brake Fluid Type and Flush Interval

By Core Brake Parts Tech Team — Circleville, OH warehouse

The Infiniti FX35 is specified for DOT 3 brake fluid. The FX owner's manual lists Genuine NISSAN Super Heavy Duty Brake Fluid or an equivalent DOT 3 fluid meeting U.S. FMVSS No. 116, and it warns against synthetic (silicone) fluid. Because DOT 3 absorbs moisture over time, plan on a full flush on the schedule in your Infiniti Service and Maintenance Guide, and sooner if the fluid is dark or the pedal feel has changed.

What Brake Fluid the FX35 Uses

In the capacities and recommended fluids table of the FX45/FX35 owner's manual, the brake fluid line reads Genuine NISSAN Super Heavy Duty Brake Fluid or equivalent DOT 3 (U.S. FMVSS No. 116). The maintenance section repeats it: if the level is below the MIN line or the brake warning light comes on, add that fluid or an equivalent DOT 3 up to the MAX line. The same page carries two warnings worth taking seriously: use only new fluid, because old or contaminated fluid can damage the brake system, and do not add synthetic brake fluid.

"Synthetic" in that warning means silicone-based DOT 5, not the glycol-based DOT 4 you see on store shelves. Federal standard FMVSS 116 requires silicone DOT 5 fluid to be dyed purple, while DOT 3, DOT 4 and DOT 5.1 glycol fluids must be colorless to amber. If you ever see purple fluid in an FX35 reservoir, someone put in the wrong fluid and the system needs a professional flush.

The owner's manual we checked covers the first-generation FX (2003 to 2008). The 2009 FX35 is a redesigned model, so on a 2009 confirm the specification printed on the reservoir cap or in that year's owner's manual before you buy fluid.

DOT 3 vs DOT 4 vs DOT 5: The Numbers That Matter

FMVSS 116 sets minimum boiling points for each grade. The dry figure applies to fresh fluid from a sealed bottle. The wet figure is measured after the fluid has absorbed about 3.7 percent water, which is roughly where an old, neglected fill ends up.

Look at the gap between the dry and wet columns. A DOT 3 fill that has soaked up moisture can lose over 100 degrees F of boiling-point margin. That is the real reason to flush: not because the fluid wears out, but because water lowers the temperature at which it boils and forms vapor in the calipers. Vapor compresses, fluid does not, and the result is a pedal that sinks toward the floor during a long downhill grade or repeated hard stops.

DOT 3, DOT 4 and DOT 5.1 glycol fluids are required to be compatible with each other, but lubrication references still advise against mixing grades, because a vehicle is designed and tested around the chemistry of its specified fluid. The simple, safe choice for an FX35 is fresh DOT 3 from a sealed container.

How Often to Flush FX35 Brake Fluid

Infiniti's online maintenance schedule for the FX35 lists brake fluid as a recurring inspection item, with inspections at intervals as short as 3,750 miles or 3 months depending on driving conditions. The owner's manual points owners to the INFINITI Service and Maintenance Guide for the full service intervals, and that guide is the authority for when your specific year calls for a replacement.

Independent of the schedule, glycol brake fluid keeps absorbing humidity from the air through hoses and the reservoir vent. Machinery Lubrication's brake fluid guide recommends changing it every one to two years to keep the system reliable. On an FX35 that is now well over a decade old, most owners have no record of when the fluid was last changed, so treat an unknown history as overdue.

Flush sooner if any of these apply:

• The fluid in the reservoir is dark brown instead of clear to light amber.
• The pedal feels soft or spongy, or sinks after repeated hard stops.
• You tow, drive mountain grades, or live in a humid climate.
• You are replacing calipers, hoses or the master cylinder, which opens the system anyway.
• You are doing a pad and rotor job and pushing the caliper pistons back, which forces old fluid back toward the ABS unit and master cylinder.

Checking and Topping Off the Reservoir

The brake fluid reservoir sits on top of the master cylinder, with MAX and MIN lines molded into the plastic. Wipe the cap clean before you open it so dirt does not fall in. Fluid level drops slowly as pads wear, because the caliper pistons move outward and hold more fluid. A level that drops noticeably between checks, or a brake warning light, points to a leak or very worn pads. The owner's manual says that if fluid must be added frequently, the system should be thoroughly checked.

Two practical cautions from the manual: do not overfill past MAX, and do not spill fluid on painted surfaces. Brake fluid damages paint, so rinse any spill with water right away.

Doing the Flush: What It Involves

A flush replaces all of the old fluid by bleeding each caliper until clean fluid comes out. On the FX35 that means four disc brake calipers plus the ABS and stability control hydraulic unit in between. A careful DIYer with a two-person pedal method or a pressure bleeder can do it in about an hour. Keep these points in mind:

1. Use a fresh, sealed bottle of DOT 3. Opened fluid that has sat on a shelf has already been absorbing moisture.
2. Follow the bleeding sequence in the factory service manual for your year, and never let the reservoir run below MIN, or you will pull air into the master cylinder and ABS unit.
3. Tighten the bleeder screws to the factory service manual value; they are small and strip easily.
4. If the pedal is still soft after bleeding, the ABS unit may be holding trapped air, and a scan-tool bleed procedure at a shop may be needed.
5. Dispose of old fluid at a parts store or recycling center, not in the drain.

If your caliper bleeders are seized or a caliper piston is sticking, this is the time to replace the caliper. Browse our replacement brake calipers and brake hoses so you only open and bleed the system once.

Pair the Flush with a Brake Inspection

Fresh fluid is wasted on worn friction parts. While the wheels are off for bleeding, measure pad thickness and check the rotors for scoring, lips and heat spots. On a 2003 FX35, also confirm that NHTSA recall 03V476000 was completed; it covered front brake caliper mounting bolts that may not have been adequately tightened, with dealers tightening the bolts as the remedy.

For 2006 to 2009 models we carry EBC Greenstuff 6000 front brake pads for the 2006-2009 FX35. For 2003 to 2005 models there are EBC Yellowstuff rear brake pads for the 2003-2005 FX35, along with EBC GD Sport slotted rear rotors and EBC USR slotted rear rotors. You can also shop all brake pads and brake rotors by vehicle.

Frequently Asked Questions

Can I use DOT 4 in my Infiniti FX35?

DOT 4 meets or exceeds every DOT 3 boiling-point minimum in FMVSS 116, and glycol grades are required to be compatible. The owner's manual still specifies DOT 3, and mixing grades is not recommended, so if you switch, do a complete flush rather than topping off, and check with your dealer first.

Is DOT 5 fluid safe in an FX35?

No. DOT 5 is silicone-based, and the FX owner's manual says not to add synthetic brake fluid. Silicone does not mix with the glycol fluid already in the system.

How do I know my FX35 brake fluid needs changing?

Dark fluid, a soft or sinking pedal, or no service record are all signs. A shop can also test moisture content with test strips or a meter. Either way, follow the replacement interval in your Service and Maintenance Guide.

Why is my FX35 brake fluid level low?

Gradual drop is normal as pads wear. A fast drop or a brake warning light means a leak or very thin pads, and the manual says the system should be checked if fluid must be added frequently.

Should I flush the fluid when I replace pads and rotors?

It is a good time to do it. Pushing the pistons back returns old fluid toward the master cylinder and ABS unit, and the wheels are already off for bleeder access.

Sources

1. Infiniti FX45/FX35 Owner's Manual - DOT 3 / FMVSS 116 specification, no synthetic fluid, top-off and paint warnings
2. INFINITI USA FX35 Brake Fluid Maintenance Schedule - brake fluid inspection intervals
3. 49 CFR 571.116 (FMVSS 116), Cornell LII - dry and wet boiling-point minimums and fluid color requirements
4. Machinery Lubrication: Brake Fluid, A Practical Guide - hygroscopic behavior, 3.7 percent wet test, mixing guidance, one-to-two-year change advice
5. NHTSA Recalls: 2003 Infiniti FX35 - recall 03V476000 front caliper mounting bolts