2002-2006 Infiniti Q45 Brake Fluid Type and Flush Interval

By Core Brake Parts Tech Team — Circleville, OH warehouse

The 2002-2006 Infiniti Q45 (the F50 generation) takes DOT 3 brake fluid. That is the fluid named in the brake section of the factory service manual, and it is what the car was filled with new. Infiniti's online maintenance lookup for the Q45 does not list a fixed mileage for replacing the fluid, but it does call for inspecting the brake lines and the pads and rotors every 15,000 miles or 12 months, and that inspection is the right time to test the fluid and decide whether it needs a flush.

What brake fluid the Q45 uses and why it matters

The F50 Q45 service manual states it plainly: the recommended fluid is DOT 3. DOT 3 is a glycol-ether fluid, and the federal standard that defines it (FMVSS 116) sets its minimum boiling points. Those minimums are the reason fluid condition matters so much on a heavy V8 sedan that does most of its braking from highway speed.

The "wet" number is the one that tells the real story. Glycol fluid pulls moisture out of the air through the reservoir vent and hose walls, and as it does, its boiling point drops toward that wet figure. Fluid that has been in a Q45 for many years can be far closer to the wet value than the dry one. When fluid near a hot caliper boils, it forms vapor bubbles that compress, and the pedal goes soft or sinks right when you need it most.

DOT 3 and DOT 4 are compatible with each other, so a top-off with DOT 4 will not harm the system. The trade publication Brake and Front End notes that all DOT 3, 4 and 5.1 fluids are compatible with each other and with all systems. Mixing does lower the boiling point of the better fluid, though, so for a full flush pick one grade and use it throughout. Never put DOT 5 silicone fluid in a Q45. It does not mix with glycol fluid and will separate out and collect in the system.

How often to flush the brake fluid on a 2002-2006 Q45

Infiniti's current online maintenance lookup for the 2003 Q45 lists brake lines and cables as "inspect every 15,000 miles or 12 months" under both standard and severe conditions, and brake pads and rotors as "inspect every 15,000 miles or 12 months" standard or "every 7,500 miles or 6 months" severe. It does not show a separate brake fluid replacement line for this model. Your printed Service and Maintenance Guide is the final word for your car, so check it if you still have it.

In practice, every Q45 still on the road is at least 20 years old, and most have fluid that has never been changed or was changed so long ago nobody knows. Treat these as flush-now signs:

• You have no record of the fluid ever being replaced.
• The fluid in the reservoir is dark brown or cloudy instead of clear to amber (the federal standard requires new DOT 3 to be colorless to amber).
• A moisture test strip or electronic tester shows the fluid is past its limit, or a copper test strip shows high copper, which points to the corrosion inhibitors being used up.
• The pedal feels soft or sinks after long downhill stops, then firms up once the brakes cool.
• You are replacing calipers, hoses or the master cylinder, and the system will be opened anyway.

After that first flush, test the fluid at every 15,000 mile or 12 month brake inspection and replace it when it fails. That keeps the change tied to the car's actual condition instead of a guess.

What to watch for when flushing a Q45

The Q45 has four-wheel disc brakes (front and rear calipers), a brake booster, and an ABS and VDC actuator in the hydraulic circuit. The factory manual gives a few cautions that apply to anyone doing this job at home:

• Protect the paint. The manual warns not to splash brake fluid on painted areas. Brake fluid can damage paint, so keep a rag under the reservoir and wipe spills right away with water.
• Never reuse drained fluid. Fluid that comes out of the bleeders goes in the waste bottle, not back in the reservoir.
• Keep the system clean. The manual says to clean hydraulic parts only with clean brake fluid and never with mineral oils such as gasoline or kerosene, which ruin the rubber seals.
• Mind the electronics. Before working on the hydraulic system, the manual calls for turning the ignition off and disconnecting the VDC actuator connectors or the battery terminals.
• Do not let the reservoir run dry. Pulling air into the master cylinder or the ABS/VDC actuator makes the bleed much harder. Follow the bleeding sequence in the service manual for your year.

A two-person pedal bleed or a pressure bleeder both work. Keep pushing fresh fluid through each bleeder until it runs clean and free of bubbles, then set the level between the reservoir marks and check the pedal before driving.

Parts to replace at the same time

A flush is a good moment to look at everything else in the hydraulic and friction side of the system, because the wheels are already off:

• Rubber brake hoses. On a car this age, check the hoses for cracking, bulging or chafing, which is exactly what Infiniti's brake line inspection covers. Replacement flexible lines are in our brake hoses collection.
• Calipers. A seized slide pin or a sticking piston often shows up as uneven pad wear or a pull. See replacement brake calipers.
• Pads and rotors. Measure pad thickness and rotor condition while you are there. For the front axle, we carry front drilled and slotted rotors for the 2002-2006 Q45 V8, and matching friction is in brake pads.
• Hardware. New clips and shims from our brake hardware kits keep new pads quiet.

How hard is the job?

A brake fluid flush on a Q45 is a moderate DIY job. You need the car safely supported on stands, the right wrench for the bleeder screws, clear tubing, a catch bottle and enough sealed, fresh DOT 3 that you never run short mid-bleed. The hard part is patience: working each corner in order, never letting the reservoir drop too low, and confirming a firm pedal at the end. If the pedal stays soft after a careful bleed, air may be trapped in the ABS/VDC actuator, and a shop with a scan tool that can cycle the actuator is the next step.

Frequently Asked Questions

Can I use DOT 4 in my Infiniti Q45?

Yes. DOT 4 is compatible with DOT 3 and has higher minimum boiling points under the federal standard. The factory spec is DOT 3, so DOT 3 is always correct, but DOT 4 is a safe choice. For a full flush, use one grade throughout rather than mixing.

Can I put DOT 5 brake fluid in a Q45?

No. DOT 5 is silicone based and does not mix with the glycol fluid the Q45 was designed for. It separates in the system. Stick with DOT 3 or DOT 4.

What color should Q45 brake fluid be?

New DOT 3 is colorless to amber. Fluid that has turned dark brown or looks cloudy has absorbed moisture and broken down, and it is due for replacement.

How often does Infiniti say to inspect the Q45 brakes?

Infiniti's maintenance lookup for the 2003 Q45 lists brake lines and cables at every 15,000 miles or 12 months, and pads and rotors at every 15,000 miles or 12 months under normal use or every 7,500 miles or 6 months under severe conditions.

Will old brake fluid cause a soft pedal?

It can. Moisture lowers the fluid's boiling point, and fluid that boils near a hot caliper forms vapor that compresses. A pedal that fades on long downhill stops and comes back after cooling is a classic sign.

Sources

1. 2003 Infiniti Q45 (F50) factory service manual, BR brake section - DOT 3 recommended fluid, paint and reuse cautions, VDC actuator precaution, front and rear disc layout
2. Infiniti USA: 2003 Q45 brake lines and cables maintenance guide - inspect every 15,000 miles or 12 months
3. Infiniti USA: 2003 Q45 brake pads and rotors maintenance guide - 15,000 miles or 12 months standard, 7,500 miles or 6 months severe
4. 49 CFR 571.116 (FMVSS 116) motor vehicle brake fluids - DOT 3, 4 and 5 dry and wet boiling points, fluid colors
5. Brake and Front End: Brake Fluid DOT 3, 4, 5 and 5.1 FAQ - DOT 3/4/5.1 compatibility, DOT 5 separation, copper as a sign of additive breakdown