1997-2001 Mitsubishi Montero Brake Fluid Type and Flush Interval

By Core Brake Parts Tech Team — Circleville, OH warehouse

The 1997-2001 Mitsubishi Montero and Montero Sport use a glycol-based DOT brake fluid, and Mitsubishi's own service bulletin says to use genuine fluid of the type listed in that vehicle's service manual, which is either DOT3 or DOT4. The quickest way to confirm yours is the rating marked on the master cylinder reservoir cap. Flush it on a time basis, not just mileage: on a truck this age, fluid that has not been changed in two years or more is almost certainly carrying enough water to lower its boiling point.

Which brake fluid the 1997-2001 Montero takes

Mitsubishi Motors North America issued Technical Service Bulletin TSB-18-35-001 in April 2018 to all Mitsubishi models. It tells technicians to use Mitsubishi genuine brake fluid and to refer to the individual vehicle service manual for the brake fluid type, DOT3 or DOT4. The only vehicles it restricts to DOT4 alone are specific late-model Eclipse and Outlander recall vehicles, not the Montero.

For a 1997-2001 Montero or Montero Sport, that comes down to three rules:

• Read the reservoir cap first. The DOT rating is marked on the cap or reservoir. Use a fresh sealed bottle of that grade.
• Never use a mineral-oil fluid. The same bulletin warns that non-genuine fluid with a mineral-based oil can swell and damage the rubber cup inside the brake master cylinder. That rules out power steering fluid, hydraulic jack oil and anything not labeled DOT.
• Do not use silicone DOT 5. It is a different chemistry from the glycol DOT3 and DOT4 these trucks were built around. Stay with the glycol grade the cap calls for.

The federal brake fluid standard, FMVSS 116, sets the minimum boiling points each grade must meet. Those minimums explain why both the grade and the age of the fluid matter:

"Wet" is the boiling point after the fluid has absorbed a controlled amount of water in testing. It is the number that matters on an old truck, because it is closer to what is actually in the lines.

How often to flush it, and why time matters more than miles

DOT3 and DOT4 are hygroscopic: they pull moisture in through hoses, seals and the reservoir vent even while the truck is parked. MISCO, which makes the refractometers shops use to test brake fluid, puts that uptake at 1% or more per year of service and says a typical two-year-old vehicle carries 2-3% water. Just 2% water drops DOT3's boiling point by about 135 F and DOT4's by about 81 F.

That is why the usual guidance is a flush every 12 to 24 months depending on the manufacturer, and MISCO's threshold is to change fluid in any vehicle once water content passes 3%. If your Montero tows, climbs mountain grades or carries a full load, change it sooner. For a Montero with an unknown service history, treat the first flush as overdue, do it now, then set a two-year reminder.

Water does more than lower the boiling point. Mitsubishi's bulletin notes that moisture and contamination in the reservoir can rust the master cylinder piston and plug its oil passages. On a truck this old, that is often the difference between a fluid service and a master cylinder replacement.

Signs the fluid on your Montero is overdue

• Dark fluid in the reservoir. Fresh DOT3 or DOT4 is clear to light amber. Brown or black fluid is old and contaminated.
• A pedal that goes soft after hard use. A long downhill or a hot towing run that leaves the pedal spongy points to water in the fluid flashing to vapor.
• Low fluid level. The level drops slowly as pads wear, but a sudden drop means a leak. Find it before you top off.
• Brake warning lamp on. The lamp can come on for low fluid level, which is a hydraulic problem until proven otherwise.
• Test results. A refractometer or a quality test strip tells you water content directly, which beats guessing by color.

Montero-specific problems to check during a flush

A fluid service is the right time to look at the parts NHTSA recall records flag on these trucks:

• Front brake lines (1997-1998 Montero). NHTSA campaign 98V220000 covered front brake lines that could develop pin holes from chafing against the edge of the pass-through hole in the inner fender, leaking fluid and lighting the brake lamp. Look closely at the lines where they pass through the inner fender. Replacement brake lines and brake hoses are the fix for any line that shows wear.
• Hydraulic booster accumulator (Montero). NHTSA campaign 01V254001 covered the accumulator on the Montero's hydraulic brake booster, which could leak its nitrogen charge. Symptoms were an abnormal noise from the left side of the dash when braking and a delayed first brake assist after the truck sat parked. That is a booster problem, so a fluid flush will not cure it.
• Vacuum hose (1999-2001 Montero Sport 3.5L). NHTSA campaign 01V027000 covered brake vacuum hoses that did not comply with FMVSS 106 and could burst. A cracked or collapsed vacuum hose gives a hard pedal and weak assist on the vacuum-boosted Montero Sport.

Before buying parts, run your VIN on the NHTSA recall lookup; a dealer may still complete an open campaign.

Doing the flush, and what to replace at the same time

A flush on these trucks is a two-person pedal-and-bleeder job, or a one-person job with a pressure bleeder. Follow the bleeding sequence and any ABS bleeding steps in the factory service manual for your exact model and equipment; the Montero and Montero Sport are different platforms and should not be assumed to bleed the same way. General points that apply to both:

1. Clean the reservoir cap and the area around it before opening it, so dirt does not fall in. Mitsubishi's bulletin specifically calls for keeping moisture and contamination out of the reservoir.
2. Pull the old fluid out of the reservoir, refill from a sealed bottle, and never let the reservoir run dry while bleeding, or you will pull air into the master cylinder.
3. Bleed each wheel until the fluid coming out is clean and free of bubbles.
4. If you use a power bleeder, keep it clean and use it only for brake fluid, as the bulletin directs.
5. Recap bottles tightly. FMVSS 116 requires every container to warn that fluid must be kept clean, dry and in its original tightly closed container. A half-used bottle that has sat open is already taking on water.

Parts worth pairing with the job:

• Bleeder screws and hardware. Seized bleeders are common on 20-year-old calipers, and brake hardware kits are cheap insurance.
• Calipers. If a bleeder snaps or a piston is rusted from wet fluid, replace the unit with one of our brake calipers rather than fighting it.
• Master cylinder. If the pedal sinks slowly under steady pressure with no external leak, the master cylinder cups are bypassing. See our master cylinders.
• Booster. For a vacuum-boosted Montero Sport with a hard pedal and a good vacuum supply, see this 1997-2001 Montero Sport vacuum power brake booster, or browse all brake boosters.

How hard is the job

A straight fluid flush is an easy-to-moderate DIY job with basic hand tools, a bleeder wrench, clear tubing and a catch bottle. The hard parts on an old Montero are stuck bleeder screws and, on ABS-equipped trucks, keeping air out of the ABS hydraulic unit; if air gets in, the factory procedure or a scan tool may be needed to clear it. If the pedal is not firm and high when you finish, do not drive the truck until it is.

Frequently Asked Questions

Can I use DOT 4 in a Montero that calls for DOT 3?

DOT 4 has higher minimum boiling points than DOT 3 under FMVSS 116, and both are glycol-based. Mitsubishi's guidance is to use the type listed for your vehicle, so match what the cap and service manual specify and avoid mixing grades, so you always know what is in the system.

How often should I change brake fluid on a 1997-2001 Montero?

On a time basis, typically every one to two years. The fluid picks up water whether you drive or not, and a flush is due once testing shows around 3% water.

Why is my Montero brake fluid black?

Old fluid darkens as it absorbs moisture and picks up contamination from seals and metal parts. Dark fluid should be flushed, not just topped off.

Can I use DOT 5 silicone fluid?

No. These trucks use glycol DOT fluid, and silicone DOT 5 is a different chemistry. Use the glycol grade shown on the reservoir cap.

My Montero makes a noise under the dash when I brake. Is that the fluid?

Probably not. NHTSA campaign 01V254001 describes that noise on the left side of the dash from a leaking hydraulic booster accumulator. Check the recall status on your VIN.

Sources

1. Mitsubishi TSB-18-35-001 (NHTSA) - genuine fluid, DOT3 or DOT4 per the vehicle service manual; mineral-oil fluid swells master cylinder cups; moisture rusts the piston
2. FMVSS 116, 49 CFR 571.116 (Cornell LII) - minimum dry and wet boiling points for DOT 3, DOT 4 and DOT 5, and the keep-clean-and-dry container warnings
3. MISCO: When to change your brake fluid - moisture uptake of 1% or more per year, effect of 2% water on boiling point, 12-24 month guidance and the 3% change threshold
4. NHTSA recall data, 1997 Montero - campaign 98V220000, front brake lines chafing at the inner fender pass-through hole
5. NHTSA recall data, 2001 Montero - campaign 01V254001, hydraulic brake booster accumulator may leak nitrogen gas
6. NHTSA recall data, 2000 Montero Sport - campaign 01V027000, 1999-2001 Montero Sport 3.5L noncompliant brake vacuum hoses