NHTSA lists 1 safety recall and 27 owner complaints for the 1998 Mitsubishi Diamante. Most complaints involve visibility (15) and vehicle speed control (3). The EPA rates it 18 mpg combined.
CERTAIN PASSENGER VEHICLES FAIL TO CONFORM TO THE REQUIREMENTS OF FEDERAL MOTOR VEHICLE SAFETY STANDARD NO. 208, 'OCCUPANT CRASH PROTECTION.' THE BILINGUAL ENGLISH/SPANISH REMOVABLE AIR BAG WARNING LABELS AFFIXED TO THE DASH AND TO THE SUNVISOR DO NOT MEET THE SIZE REQUIREMENTS OF THE STANDARD.
Complaints are unverified owner reports to NHTSA and are not normalized for sales volume. One complaint can cite several components.
“THIS IS THE SECOND TIME THE HEATER CORE HAS STARTED TO LEAK. IT WAS REPLACED 40K MILES AGO AND I WAS CHARGED $ 1,000 FOR REPAIR COSTS. HAVING RESEARCHED THIS, IT IS DUE TO FAULTY HEATER CORE GASKETS WHICH MITSUBISHI REPLACED THE DEFECTIVE GASKETS WITH A REDESIGNED ONE. THE CAR IS UNDRIVABLE DUE TO THE TOXIC FUMES FROM THE ETHYLENE GLYCOL COMING OUT OF ALL THE VENTS AND I DO NOT HAVE THE MONEY TO GET IT REPAIRED. MITSUBISHI REFUSES TO DO ANYTHING ABOUT IT, AND NEARLY EVERY DIAMANTE ON THE ROAD HAS HAD THIS HAPPEN. THE CARPET IS RUINED FROM THE COOLANT LEAK AS WELL, AND MANY HAVE HAD THE ECU FOR THE TRANSMISSION FAIL DUE TO COOLANT LEAKING ON IT. *TR”
“WE JUST CLEARED CANADIAN CUSTOMS AT BLAINE WA, PACIFIC CROSSING, AND WERE ACCELERATING TO SPEED LIMIT ON I 5 FREEWAY WHEN THE CAR ACCELERATED TO NEAR 100 MILES AN HOUR. THE TACH AT SOME POINT WAS 7500 AND INCREASING. THE ACCELERATOR WAS STUCK AND EVENTUALLY WE WERE ABLE TO GET TO THE EMERGENCY LANE AREA AND TURNED OF THE IGNITION KEY. FULL PRESSURE ON THE BRAKES WOULD NOT SLOW IT DOWN MUCH. *TR WE WERE TOWED 21 MILES TO DAVIS AUTOMOTIVE IN BELLINGHAM, WA, WHERE A REPLACEMENT THROTTLE CABLE AND ASSOCIATED STRUCTURE WAS SEVERELY BENT AND THE CABLE HAD CUT THRU IT AND STUCK. *MEC THE CONSUMER HAD THE VEHICLE TOWED WHERE A REPLACEMENT THROTTLE CABLE WAS INSTALLED. UPDATED 10/10/08. *JB”
“BRAKE PADS PREMATURE WEAR, AND BRAKE ROTORS HAVE WARPED AT LEAST 10 TIMES. *AK”
Towing, payload and dimensions aren’t in the EPA or NHTSA data, so we don’t list them.
| Version | City | Hwy | Comb. | Fuel / yr | CO₂ g/mi |
|---|---|---|---|---|---|
| Diamante Auto 4-spd, 6 cyl, 3.5 L · Front-Wheel Drive | 16 | 23 | 18 | $4,200 | 494 |
| Item | Miles | Time | Note |
|---|---|---|---|
| Engine oil & filter | 5,000–10,000 mi | 6–12 months | Follow the oil-life monitor if fitted |
| Tire rotation | 5,000–7,500 mi | Every oil change | Check pressure monthly |
| Engine air filter | 15,000–30,000 mi | 1–2 years | Sooner in dusty areas |
| Cabin air filter | 15,000–25,000 mi | 1–2 years | |
| Brake fluid | — | 2–3 years | Absorbs moisture over time |
| Coolant | 60,000–100,000 mi | 5–10 years | Long-life coolants last longer |
| Spark plugs | 60,000–100,000 mi | — | Iridium/platinum plugs at the long end |
| 12V battery | — | 3–5 years | Heat shortens battery life |
1 safety recall as of Nov 11, 2026, according to NHTSA. Recall repairs are free at a dealer. Check your VIN to see whether your car is included and whether the repair was done.
Owners filed 27 complaints with NHTSA. The most-cited components are visibility (15), vehicle speed control (3), service brakes, hydraulic (3). Complaints are unverified owner reports and aren't adjusted for how many cars were sold.
The EPA rates the 1998 Mitsubishi Diamante at 18 mpg combined, depending on engine and drivetrain (1 version rated).