The 1990 Q45 was Infiniti's flagship with a sophisticated 4.5L V8 and advanced electronics, but age has made hydraulic lifter failure, transmission cooler leaks, and timing belt maintenance the dominant concerns for survivors.
Hydraulic Valve Lifter Collapse and Engine Noise
Common · high severityTypical onset: 80,000-150,000 mi
Symptoms: Loud ticking or tapping from valve covers, especially cold start, Loss of power and rough idle, Check engine light with misfire codes, Eventually progresses to complete lifter failure and bent valves
Fix: Requires removing both valve covers and camshafts to replace all 32 hydraulic lifters. Quality OEM or Nissan lifters are critical—aftermarket often fail quickly. This is a 12-14 hour job if you're doing it right with proper cam timing verification. If lifters have already damaged valves, you're looking at head removal and valve work adding another 8-10 hours.
Estimated cost: $2,800-4,500
Timing Belt Failure and Interference Engine Damage
Common · high severityTypical onset: 60,000-90,000 mi intervals
Symptoms: No symptoms until catastrophic failure, Engine suddenly dies and won't restart, If belt breaks: bent valves, damaged pistons, potential complete engine rebuild needed
Fix: This is an interference engine—if the timing belt snaps, valves hit pistons. Preventive timing belt service (belt, tensioner, water pump, seals) is 8-10 hours. If the belt has already failed, you're looking at head removal, valve replacement, and often piston/ring work. Many owners end up with short block replacements or complete rebuilds at $6,000-10,000. Do the belt every 60k religiously.
Estimated cost: $1,200-1,800 preventive / $6,000-10,000 after failure
Transmission Oil Cooler Line and Radiator Tank Leaks
Common · medium severityTypical onset: 100,000-180,000 mi
Symptoms: Pink or red fluid dripping under engine bay, Transmission fluid in coolant reservoir (milky appearance), Transmission overheating or erratic shifting, Low transmission fluid level
Fix: The cooler lines crack at fittings and the internal radiator transmission cooler can fail, causing fluid cross-contamination. Line replacement is straightforward (2-3 hours), but if the radiator tank has failed and ATF mixed with coolant, you need radiator replacement, complete fluid flush of both systems, and sometimes transmission filter service. Total 4-6 hours if doing it all.
Estimated cost: $400-800 lines only / $1,200-1,800 with radiator and flush
Transmission Mount Deterioration and Driveline Vibration
Common · low severityTypical onset: 70,000-120,000 mi
Symptoms: Clunking when shifting from Park to Drive or Reverse, Vibration at idle in gear, Excessive driveline movement during acceleration, Visible cracking or fluid leakage from hydraulic mount
Fix: The rear transmission mount is hydraulic-filled and fails commonly. Replacement requires supporting the transmission and unbolting the crossmember—about 2-3 hours. OEM mounts last longer than aftermarket. While you're there, inspect the front engine mounts as they wear similarly.
Estimated cost: $350-600
Fuel System Degradation and Hard Starting
Occasional · medium severityTypical onset: 120,000+ mi
Symptoms: Extended cranking before engine fires, especially when warm, Rough idle and hesitation after sitting, Fuel smell from engine bay, Loss of fuel pressure after shutdown
Fix: Fuel filter clogs, fuel pressure regulator diaphragms fail, and injector o-rings leak on these aged V8s. Filter replacement is 1 hour. Regulator is another 1.5 hours. If you have leaking injectors, budget 4-6 hours to pull the upper intake plenum and replace all o-rings and seals. In-tank fuel pump can also weaken—that's a 3-4 hour tank-drop job.
Estimated cost: $150-300 filter/regulator / $800-1,400 full injector service / $600-900 fuel pump
Active Suspension Component Failure
Occasional · medium severityTypical onset: 90,000-140,000 mi
Symptoms: Suspension warning light illuminated, Loss of ride height adjustment, Harsh ride or excessive body roll, Hydraulic fluid leaks at struts or actuators
Fix: The 1990 Q45 came with Nissan's Full Active Suspension on some trims—hydraulic actuators, accumulators, and a complex control system. When components fail, replacement parts are scarce and expensive. Many owners convert to conventional coilovers (8-10 hours labor for full conversion). OEM repair of individual struts runs 4-6 hours per corner if parts are available.
Estimated cost: $1,500-2,500 per strut OEM / $2,000-3,500 full coilover conversion
Alternator and Charging System Failure
Occasional · medium severityTypical onset: 100,000-150,000 mi
Symptoms: Battery warning light, Dimming headlights or interior lights, Dead battery after short trips, Voltage gauge reading low (below 13.5V)
Fix: The alternator is tucked low on the passenger side and requires removing the lower splash shield and working from underneath. Not terrible but tight access makes it a 2-3 hour job. Test the battery and connections first—these cars have multiple ground points that corrode and mimic alternator failure.
Estimated cost: $450-700
Only buy if timing belt and lifters have been recently done with receipts—otherwise you're inheriting a $5,000-8,000 engine refresh on a 35-year-old luxury car with scarce parts.
AI-assisted summary drawn from NHTSA recall data, our labor-times database, and platform knowledge. Not a substitute for a pre-purchase inspection on a specific vehicle.