The 2018 Ram 3500 with the 6.7L Cummins is a workhorse diesel known for engine reliability, but the 68RFE automatic transmission and its supporting components are where most owners encounter expensive problems, especially under heavy towing or frequent payload work.
68RFE Transmission Overheating and Failure
Common · high severityTypical onset: 80,000-150,000 mi
Symptoms: Transmission temperature spikes above 220°F under load or towing, Harsh or delayed shifts, especially 5th to 6th gear, Slipping between gears or loss of power during acceleration, Burnt transmission fluid smell or dark fluid on dipstick
Fix: Root cause is often undersized factory cooler combined with torque converter clutch wear. Full fix includes upgraded auxiliary cooler installation, fluid/filter service, and in severe cases torque converter replacement or full rebuild. Rebuild labor runs 18-24 hours.
Estimated cost: $800-1,500 for cooler upgrade and fluid service; $3,500-6,500 for torque converter or full rebuild
Transmission Oil Cooler Line Failure
Occasional · high severityTypical onset: 60,000-120,000 mi
Symptoms: Red transmission fluid pooling under vehicle, usually passenger side, Transmission fluid level dropping rapidly, Loss of forward gears or no movement after fluid loss, Metal cooler lines corroded or split at crimp points
Fix: Factory steel lines rust through at mounting points and crimps, especially in salt states. Requires line replacement (2-3 hours) and full fluid refill. If driven low on fluid, internal damage may require rebuild.
Estimated cost: $400-700 for lines and fluid; add $4,000-6,000 if internal damage occurred
Transmission Mount Deterioration
Common · medium severityTypical onset: 70,000-130,000 mi
Symptoms: Clunk or bang when shifting from park to drive or reverse, Excessive vibration at idle in gear, Visible sagging or torn rubber on transmission crossmember mount, Driveline shudder during acceleration
Fix: Rubber transmission mount degrades from engine torque and heat cycles. Common on trucks used for towing. Replacement takes 1.5-2 hours, requires supporting transmission and dropping crossmember.
Estimated cost: $250-450
Shift Solenoid and Overdrive Solenoid Failure
Occasional · medium severityTypical onset: 90,000-140,000 mi
Symptoms: Check engine light with codes P0750-P0765 (shift solenoid range), Stuck in one gear or limp mode (usually 3rd gear), Erratic shifting patterns or refusal to shift into overdrive, Delayed engagement when cold
Fix: Solenoid pack inside transmission valve body fails from heat and debris contamination. Requires transmission pan removal, valve body dropout, and solenoid replacement. 4-6 hours labor, often combined with full fluid/filter service.
Estimated cost: $800-1,400
Fuel Filter Housing Leaks and Air Intrusion
Common · medium severityTypical onset: 50,000-100,000 mi
Symptoms: Hard starting or extended cranking, especially after sitting overnight, Rough idle or loss of power under acceleration, Fuel weeping or diesel smell around filter housing on driver frame rail, Air bubbles visible in clear fuel return line
Fix: Factory fuel filter housing develops cracks or o-ring failures allowing air into system. Aftermarket billet housing upgrade recommended over OEM plastic replacement. Filter service is 0.5 hours; housing swap adds 1-1.5 hours.
Estimated cost: $150-300 for OEM housing; $400-600 for upgraded billet housing with install
Shift Cable Binding and Detachment
Occasional · medium severityTypical onset: 60,000-110,000 mi
Symptoms: Shifter feels loose, sloppy, or stuck in one position, Gear indicator on dash doesn't match actual shifter position, Cannot shift out of park or difficulty moving through gears, Cable housing detached from transmission bracket
Fix: Cable end bushing wears or cable housing pulls out of bracket at transmission. Column-shift models more prone than console-shift. Replacement is 1.5-2 hours including adjustment and road test.
Estimated cost: $250-450
Buy it for the bulletproof Cummins, but budget $2,000-3,000 for transmission preventive upgrades if you're towing—the 68RFE is the weak link in an otherwise solid platform.
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.