1991-1993 Mitsubishi 3000GT Brake Fluid Type and Flush Interval

By Core Brake Parts Tech Team — Circleville, OH warehouse

The 1991-1993 Mitsubishi 3000GT takes DOT 3 brake fluid. Mitsubishi's 1991 service manual lists the brake fluid as "conforming to DOT3." A good DOT 4 also meets that requirement and handles heat better. On a car this old, flush the system now if you have no record of the last flush, then every two to three years after that.

This guide covers what the factory calls for, why DOT 4 is a safe upgrade, which fluid to keep out of the system, how often to change it, and what to check while the wheels are off.

What Brake Fluid the 1991-1993 3000GT Uses

The brake section of the 1991 3000GT service manual lists the fluid as "Brake fluid: Conforming to DOT3." DOT 3 and DOT 4 are both glycol-based fluids. Federal rules (FMVSS 116) set a minimum boiling point for each grade. A fluid only has to meet that minimum to wear the label. The table shows the minimums:

The "wet" number is the one that matters on a street car. It is the boiling point after the fluid has picked up moisture, and brake fluid starts picking up moisture the day it goes in. DOT 4 beats the DOT 3 wet minimum by 15 C. That extra margin helps a heavy car like a 3000GT, especially the all-wheel-drive VR-4, on long downhill runs or hard back-road driving.

Brembo still says the best approach is to use the fluid the carmaker recommends. Both DOT 3 and DOT 4 are glycol-based, but their chemistry differs. The simple way to handle this: pick one fluid and flush the whole system to it. Don't keep topping off a DOT 3 system with a mix of whatever bottles are on the shelf.

Why the Flush Interval Matters on This Car

Glycol brake fluid absorbs water. Brembo explains that the fluid pulls moisture from the air through the porosity of the brake lines, and its boiling point drops over time as a result. Every one of these cars is now more than 30 years old. Unless the car has clear service records, assume the fluid in it is well past its useful life.

Wet fluid causes two problems:

• Fade under heat. Once the fluid boils in the calipers, the pedal goes soft or sinks during a hard stop, right when you need the brakes most.
• Internal corrosion. Water in the fluid attacks caliper bores, master cylinder bores, and on ABS-equipped cars the valves inside the hydraulic unit. The 1991 manual covers checking that ABS hydraulic unit with the Mitsubishi MUT scan tool, which gives you an idea of how much precision hardware sits in the fluid path.

Brembo's general advice is to replace brake fluid every 2 to 3 years, following the vehicle maker's schedule where one exists. For a 3000GT that is driven hard, sees track days, or sits for months at a time, use the short end of that range.

Signs the Fluid Is Overdue

• Dark brown or cloudy fluid in the master cylinder reservoir. Fresh DOT 3 or DOT 4 is close to clear, with a light amber tint.
• A pedal that feels spongy, or one that gets softer as the brakes heat up on a long stop or a downhill grade.
• A brake warning light with the fluid level low. That usually means worn pads or a leak, not old fluid. Find the cause before you top off.
• No flush in the service records, or no records at all. At this age, that alone is reason enough.

A spongy pedal can also come from air in the lines, aging rubber brake hoses that swell under pressure, or a tired master cylinder. A flush often fixes the feel. If it doesn't, work through those parts next.

How to Flush the Brake Fluid on a 3000GT

1. Buy enough fresh fluid. Use sealed bottles of DOT 3 or DOT 4. The federal label rules require the warning to keep the container clean and tightly closed so the fluid does not absorb moisture. Don't use a half-used bottle that has sat open on a shelf.
2. Clean the reservoir cap area. Remove old fluid from the reservoir and refill it with fresh fluid. Keep the level up the whole time so no air gets drawn into the master cylinder.
3. Bleed each wheel in the order given in the factory service manual. The 1991 manual's brake section includes a full bleeding procedure (it refers readers to page 35-48). Push old fluid through each caliper until clean fluid comes out.
4. ABS cars: the ABS hydraulic unit holds fluid too. A normal pressure or pedal bleed replaces most of it. If air ever got into the unit, for example because the reservoir ran dry, you may need the factory procedure and a scan tool that can cycle the valves.
5. Torque and check. If you opened any brake line, the manual gives 15 Nm (11 ft-lb) for the brake tube flare nut. Close the bleeders snugly, wipe up any spilled fluid right away (it damages paint), and check for a firm pedal before driving.

Difficulty: this is a moderate driveway job with a helper or a one-person bleeder kit. Budget about an hour. If a bleeder screw is seized or rounded, soak it with penetrant and use a six-point wrench. Snapping a bleeder turns a flush into a caliper replacement.

What to Check or Replace at the Same Time

• Brake hoses. Rubber hoses on a car this age can crack on the outside and swell on the inside. If they look weathered, fit new brake hoses while the system is open anyway.
• Calipers. A caliper that drags, leaks at the piston boot, or has a bleeder that won't free up is due. See our brake calipers.
• Master cylinder. If the pedal slowly sinks at a stop after the flush, the master cylinder is bypassing internally. Browse master cylinders.
• Pads and rotors. The 3000GT uses disc brakes at all four corners. The rear rotors also serve as small drums for the parking brake shoes, and the manual lists a 168.0 mm standard drum inside diameter and a 169.0 mm limit. If pads are low or rotors are scored, our 1991-1993 Mitsubishi 3000GT front and rear brake kit does all four corners in one order. You can also shop brake pads and brake rotors on their own.

Frequently Asked Questions

Can I use DOT 4 in a 1991-1993 3000GT that calls for DOT 3?

Yes. DOT 4 is glycol-based like DOT 3 and exceeds both the dry and wet boiling point minimums set for DOT 3. For the cleanest result, flush the whole system to DOT 4 instead of mixing the two in the reservoir.

Can I use DOT 5 silicone fluid?

No. DOT 5 is silicone-based and does not mix with the glycol fluid this system was designed for. Adding it on top of DOT 3 or DOT 4 can cause a bad pedal and seal problems.

How often should I change the brake fluid?

Brembo generally recommends every 2 to 3 years. On a 3000GT with unknown history, do it now, then set a two-year reminder. Change it more often if the car sees track use.

Does a flush fix a spongy pedal?

Often, if the cause is moisture or air in the fluid. If the pedal is still soft after a proper bleed, look at swollen rubber hoses, a sticking caliper, or a worn master cylinder.

Do I need a scan tool to bleed an ABS-equipped 3000GT?

Not for a routine flush where the reservoir never ran dry. If air got into the ABS hydraulic unit, follow the factory service manual procedure. That can require a tool that cycles the ABS valves.

Sources

1. Mitsubishi 3000GT 1991 Service Manual, Service Brakes - brake fluid conforming to DOT3
2. Mitsubishi 3000GT 1991 Service Manual, Service Brakes (master cylinder) - bleeding procedure reference and 15 Nm / 11 ft-lb brake tube flare nut torque
3. Mitsubishi 3000GT 1991 Service Manual, Service Brakes (ABS) - ABS hydraulic unit inspection with the MUT tester
4. Mitsubishi 3000GT 1991 Service Manual, Parking Brake - rear drum-in-hat parking brake, 168.0 mm standard and 169.0 mm limit drum diameter
5. 49 CFR 571.116 (FMVSS 116), Motor vehicle brake fluids - DOT 3, DOT 4 and DOT 5 minimum dry and wet boiling points and container moisture warning
6. Brembo, Brake fluid for cars - moisture absorption through brake lines, 2 to 3 year replacement, stick to the maker's specified fluid