Age-related electrical failures — sensors, relays, and connectors
high- Typically appears
- Any mileage on a 25+ yr old car
- Estimated repair
- $150 – $800
1998 INFINITI
QSedan
4.1L V8 · Sedan
The 1998 Infiniti Q45 is the second-generation (F50 platform, 1997–2001) version of Infiniti's flagship full-size luxury sedan. Nissan built it to compete directly with the BMW 7 Series and Mercedes-Benz S-Class, and while it never matched those two in prestige or sales volume, it delivered genuine performance and a plush interior at a significantly lower price point. Under the hood sits a 4.1L V8 producing 266 horsepower — smooth, refined, and capable of effortless highway cruising. By 1997 Infiniti redesigned the Q45 with a more conventional front grille (dropping the grille-less 'stealth' nose of the first generation) and added Active Full-Active Suspension as an option. The result was a more traditional luxury-sedan look that appealed to buyers who found the original too avant-garde. It's a big, comfortable, rear-wheel-drive car with all the expected luxury features of the era. Today, a well-maintained 1998 Q45 is a bargain luxury cruiser. Parts availability is reasonable through Nissan/Infiniti dealers and online suppliers. The flip side: repair costs can be steep when complex electronics or suspension components fail, and these cars are now over 25 years old — deferred maintenance is the norm on most survivors.
Reliability
3/5
Verified data
Engine
4.1L V8
Drivetrain
RWD
Fuel
Gasoline
MPG
17 city / 23 hwy / 19 combined
Seats
5
Doors
4
Body
Sedan
MSRP
$50,900
Overview
AI-curatedThe 1998 Infiniti Q45 is the second-generation (F50 platform, 1997–2001) version of Infiniti's flagship full-size luxury sedan. Nissan built it to compete directly with the BMW 7 Series and Mercedes-Benz S-Class, and while it never matched those two in prestige or sales volume, it delivered genuine performance and a plush interior at a significantly lower price point. Under the hood sits a 4.1L V8 producing 266 horsepower — smooth, refined, and capable of effortless highway cruising. By 1997 Infiniti redesigned the Q45 with a more conventional front grille (dropping the grille-less 'stealth' nose of the first generation) and added Active Full-Active Suspension as an option. The result was a more traditional luxury-sedan look that appealed to buyers who found the original too avant-garde. It's a big, comfortable, rear-wheel-drive car with all the expected luxury features of the era. Today, a well-maintained 1998 Q45 is a bargain luxury cruiser. Parts availability is reasonable through Nissan/Infiniti dealers and online suppliers. The flip side: repair costs can be steep when complex electronics or suspension components fail, and these cars are now over 25 years old — deferred maintenance is the norm on most survivors.
Known for
- Silky 4.1L V8 with strong low-end torque
- Exceptionally smooth, quiet highway ride
- Feature-rich luxury equipment for its era
- Rear-wheel-drive dynamics uncommon in its class at the time
Best for
- Highway cruising and long-distance comfort
- Luxury on a budget — buying used at a fraction of original MSRP
- Enthusiasts who appreciate Japanese engineering in a full-size RWD sedan
- Owners willing to perform proactive maintenance on an older vehicle
Watch for
- Age-related electrical gremlins — 25+ year-old wiring and connectors
- Active suspension system (if equipped) is expensive to repair or diagnose
- Rust underneath from Wisconsin road salt on any example that spent winters here
- High repair costs relative to current market value of the car
Common issues by mileage
6 knownOxygen (A/F) sensor failure or heater circuit fault
high- Typically appears
- 80k–150k mi
- Estimated repair
- $200 – $550
Timing and VTC (valve timing) system faults — sludge or worn tensioners
medium- Typically appears
- 90k–160k mi
- Estimated repair
- $600 – $1,800
Active Full-Active Suspension failure (if equipped)
high- Typically appears
- 80k+ mi
- Estimated repair
- $800 – $3,500
Cooling system degradation — radiator, hoses, thermostat
high- Typically appears
- Any mileage given vehicle age
- Estimated repair
- $300 – $900
Underbody rust — subframe, exhaust, brake lines
high- Typically appears
- Any — especially Midwest/Wisconsin cars
- Estimated repair
- $400 – $2,500
Maintenance schedule
- 1 Every 5,000 miles or 6 months Engine oil and filter change
The 4.1L V8 is sensitive to oil quality. Sludge buildup from extended drain intervals is a leading cause of timing and VTC system problems on high-mileage examples. Use a quality full-synthetic 5W-30.
- 2 Every 2 years Coolant flush
Old coolant turns acidic and attacks aluminum components. On a 25-year-old car, the cooling system should be inspected and flushed immediately if history is unknown.
- 3 Every 30,000 miles Transmission fluid and filter service
The 4-speed automatic is durable but neglected fluid causes shift harshness and premature wear. Drain-and-fill (not flush) is preferred on high-mileage units with unknown history.
- 4 Every 2 years Brake fluid flush
Brake fluid absorbs moisture over time, lowering boiling point and accelerating internal caliper and master cylinder corrosion — especially important in wet Wisconsin winters.
- 5 Immediately if not recently done; inspect every 2 years Inspect and replace all rubber — belts, hoses, vacuum lines
At 25+ years old, original or early-replacement rubber is overdue. Cracked hoses and vacuum leaks cause a cascade of drivability problems and false fault codes.
- 6 Every fall before winter Battery load test and terminal cleaning
Cold Wisconsin winters are hard on aging batteries. A battery that passes a simple voltage test can still fail a cold-crank test. Replace proactively if older than 4 years.
- 7 Every spring after Wisconsin winter Inspect underbody, brake lines, and exhaust for rust
Road salt accelerates corrosion on steel brake lines and exhaust components. A failed steel brake line is a safety emergency — catch it before it happens.
- 8 Every fall Inspect and lubricate door seals and weatherstripping
Original rubber seals are brittle at this age. Lubricating with silicone protectant prevents cracking and helps doors seal out Wisconsin cold and moisture.
Always defer to the manufacturer's service manual for warranty-mandated intervals.
Cost of ownership
Annual maintenance
$1,000 – $3,500
Fuel
At ~19 MPG combined and typical Wisconsin driving, expect $2,000–$2,800/year at current mid-grade fuel prices.
Insurance
Full-size luxury sedan with low current market value; liability-only coverage is common on these. Full coverage typically runs $800–$1,400/year depending on history and coverage level.
The Q45 looks cheap to buy ($3,000–$8,000 for a decent example), but ownership costs can be high relative to that purchase price. Unexpected repairs on a 25-year-old luxury car with complex electronics and optional active suspension can easily exceed the car's value. Budget generously — $1,500–$3,500/year in maintenance and repairs is realistic, more if the car has been neglected.
Seasonal care
Lake Geneva, WI Winter
- Load-test the battery every fall — the 4.1L V8 puts heavy demand on the charging system and sub-zero starts will expose a weak battery immediately.
- Switch to full-synthetic 5W-30 or 0W-30 if not already used — conventional oil thickens at Wisconsin lows and slows oil delivery to valvetrain on startup.
- Flush brake fluid and inspect steel brake lines before winter; salt-accelerated corrosion on aging lines is a real danger.
- Top off windshield washer fluid with a -20°F or lower rated formula — standard fluid freezes in the reservoir and on the windshield.
- Inspect wiper blades and consider winter-style blades to handle heavy snow without ice bridging.
- Rinse the undercarriage frequently during and after salt events — this car's age means underbody rust protection is minimal or gone.
Summer
- Check tire pressure after the first warm week — pressure rises roughly 1 PSI per 10°F temperature increase, causing overinflation on hot pavement.
- Inspect the A/C system charge and cabin filter; the evaporator on a 25-year-old car may be slow to cool or have a refrigerant leak.
- Watch coolant temperature closely on hot days — aging hoses and a marginal thermostat can push a V8 this size into overheat territory in traffic.
- Check power steering fluid level; heat causes aging seals to weep, and low fluid causes pump whine and steering slop.
Comparable vehicles
1998 Lexus
LS 400
Direct competitor in the Japanese full-size luxury sedan segment. The LS 400 is generally considered more reliable and has better parts support, but commands a higher used price for the same reason.
1998 BMW
740i
German full-size RWD luxury sedan with similar performance and feature set. Higher prestige but significantly more expensive to repair; a used Q45 buyer priced out of a 7 Series should weigh repair cost differences carefully.
No catalog match1998 Mercedes-Benz
S420
Comparable full-size luxury sedan, V8-powered and RWD. The W140 S-Class is overbuilt and long-lived but parts and labor costs are higher than the Q45.
No catalog match
1998 Cadillac
DeVille
Domestic full-size luxury sedan at a similar price point. FWD versus the Q45's RWD; more parts availability and cheaper repairs, but a different driving character entirely.
If you're shopping for one
Red flags
- No service records or vague maintenance history — on a 25-year-old luxury car, this almost always means deferred maintenance.
- Uneven suspension ride height or a bouncy, floaty feel — signs the active suspension (if equipped) is failing.
- Oil cap with milky residue or overheating history — head gasket issues on an already high-cost repair platform.
- Rust bubbling through paint on rocker panels, wheel arches, or trunk lid — indicates deeper structural corrosion underneath.
- Any live camshaft timing or VTC-related fault codes at time of purchase — these are expensive to diagnose and repair properly.
- Price that seems too good — at this age and this complexity, a suspiciously cheap Q45 almost always has hidden deferred maintenance or a known major fault.
What to inspect
- Pull all four wheels and inspect steel brake lines and the flexible hoses at each corner for rust, bubbling, or weeping — failure is a safety emergency.
- Check under the car for subframe and floor pan rust, particularly at the rear suspension mounting points.
- Verify the A/C blows cold and that the suspension doesn't wallow, clunk, or sit unevenly — active suspension repairs can exceed the car's value.
- Ask for full service records and specifically look for evidence of regular oil changes; sludged engines on these V8s are expensive to remediate.
- Scan for fault codes before purchase — particularly camshaft/VTC codes (P0012, P0015, P0022, P0025) which signal oil maintenance neglect.
- Test all electronics: windows, sunroof, heated seats, HVAC modes — sourcing switches and modules for a 25-year-old low-volume model can be difficult and expensive.