The 1990 D350 is a workhorse truck split between the legendary first-gen Cummins 12-valve diesel and Dodge's less-stellar gas V8s. Cummins models are highly sought after but bring their own cooling and transmission challenges, while gas trucks suffer from typical Chrysler small-block oiling issues under heavy load.
46RH/47RH Transmission Failure Behind Cummins
Common · high severityTypical onset: 100,000-150,000 mi
Symptoms: slipping on 3-4 shift under load, no overdrive engagement, burnt fluid smell, harsh 2-3 shift or flare
Fix: The Chrysler A518/46RH transmission was never engineered for Cummins torque. Clutch packs burn out, overdrive units fail. Expect 12-18 hours for R&R and rebuild with heavy-duty clutches, bands, and valve body upgrades. Many owners go straight to a built unit.
Estimated cost: $2,800-4,500
Cummins Killer Dowel Pin (KDP)
Occasional · high severitySymptoms: sudden catastrophic engine noise, loss of oil pressure, engine seizes, metal shavings in oil
Fix: The front gear-case dowel pin can back out and drop into timing gears, destroying the engine. Prevention requires timing cover removal and installing a tab or safety wire—about 4-6 hours. If it fails, expect full engine teardown or replacement.
Estimated cost: $150-300 preventive, $8,000+ if catastrophic
5.9L Gas V8 Bearing and Oiling Problems
Common · high severityTypical onset: 80,000-140,000 mi
Symptoms: knocking on cold start that fades, rod knock under load, low oil pressure at idle when hot, metal in filter
Fix: The LA-series 360 has marginal oiling under sustained heavy load, especially when towing. Main and rod bearings wear prematurely. Full rebuild with upgraded oil pump, bearings, and careful clearances runs 25-35 hours. Many opt for reman long block.
Estimated cost: $3,500-6,000
Transmission Cooler Line Corrosion and Leaks
Common · medium severityTypical onset: varies, age-related
Symptoms: ATF puddles under truck, low fluid warnings, burnt smell after highway driving, transmission overheating
Fix: Steel cooler lines rust through where they pass the crossmember and at radiator connections. Replacement requires custom flaring or pre-bent aftermarket lines—2-3 hours. Critical to catch early before transmission damage from low fluid.
Estimated cost: $200-400
Cummins Fuel Lift Pump Failure
Common · medium severityTypical onset: 60,000-120,000 mi
Symptoms: hard starting after sitting, loss of power under load, surging at highway speed, won't start when hot
Fix: The mechanical lift pump on the side of the block wears out diaphragm and check valves. Engine will run but starves injection pump, causing premature wear. Replace with OEM or upgrade to electric auxiliary—1.5-2 hours.
Estimated cost: $150-350
Cracked Exhaust Manifolds (Gas Engine)
Occasional · low severityTypical onset: varies, heat-cycle related
Symptoms: ticking noise on cold start, exhaust smell in cab, visible cracks on manifold surface, failed emissions test
Fix: Cast iron manifolds crack between ports from thermal cycling. Not safety-critical but noisy and annoying. Aftermarket headers or good used manifolds, 3-4 hours per side with seized studs factored in.
Estimated cost: $400-700
Steering Box Wear and Play
Common · medium severityTypical onset: 100,000+ mi
Symptoms: excessive play at center, wandering on highway, clunking over bumps, 2-3 inches of wheel slop
Fix: Recirculating ball boxes wear internally and adjustments only help temporarily. Replace with reman or upgraded unit—2-3 hours including alignment. Critical for towing safety.
Estimated cost: $350-600
Buy a Cummins model if you can verify it's had the right preventive work—they're legendary for a reason; avoid high-mileage gas V8s unless you're prepared for an engine rebuild.
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.