The 2004 Sienna is built on Toyota's second-gen platform with the 3.3L V6, generally reliable but plagued by two major issues: catastrophic engine oil sludge failures and transmission oil cooler leaks that can destroy the transmission.
Engine Oil Sludge and Premature Engine Failure
Common · high severityTypical onset: 80,000-150,000 mi
Symptoms: Check engine light with low oil pressure codes, Knocking or ticking noise from engine especially on cold starts, Oil consumption between changes (1+ quart per 1000 mi), Complete engine seizure in severe cases
Fix: The 3.3L V6 is notorious for oil sludge buildup even with regular maintenance, leading to spun bearings, scored cylinder walls, and total failure. Requires complete engine rebuild or replacement. Short block replacement takes 18-24 hours, full rebuild 25-35 hours.
Estimated cost: $4,500-7,500
Transmission Oil Cooler Internal Leak (Pink Milkshake)
Common · high severityTypical onset: 100,000-180,000 mi
Symptoms: Pink or strawberry milkshake-looking fluid in radiator, Transmission slipping, delayed engagement, or harsh shifts, Transmission overheating, Coolant in transmission pan or transmission fluid in coolant reservoir
Fix: Internal radiator failure allows coolant and ATF to mix, contaminating the entire transmission. Requires radiator replacement, complete transmission flush or rebuild, and oil cooler line replacement. If caught early (just radiator), 4-6 hours. If transmission contaminated, add 12-18 hours for rebuild. Many shops recommend transmission replacement once contaminated.
Estimated cost: $800-1,200 (early catch), $3,500-5,500 (with transmission damage)
Transmission Mount Failure
Common · medium severityTypical onset: 90,000-140,000 mi
Symptoms: Loud clunk when shifting from Park to Drive or Reverse, Vibration during acceleration especially from stop, Visible engine/transmission movement when shifting, Knocking noise over bumps
Fix: The rear transmission mount (dogbone mount) fails regularly due to engine torque and age. Relatively straightforward replacement but requires supporting the powertrain. 2-3 hours labor.
Estimated cost: $300-550
Power Sliding Door Failures
Occasional · medium severitySymptoms: Door opens or closes partially then reverses, Door won't latch or stay closed, Grinding or clicking noises during operation, Error messages or beeping without door movement
Fix: Cable stretching, motor failure, or track/roller wear causes malfunctions. Diagnosis can be time-consuming (1-2 hours). Cable replacement is 3-4 hours per side, motor is 2-3 hours. Rollers and tracks add more labor. Many owners disable the power function and use manual mode.
Estimated cost: $400-1,200 per door
Lower Ball Joint Wear
Common · medium severityTypical onset: 80,000-120,000 mi
Symptoms: Clunking noise from front suspension over bumps, Wandering or loose steering feel, Uneven tire wear on inside edges, Failed state inspection for excessive play
Fix: Ball joints are not serviceable separately on this generation; requires entire lower control arm replacement per side. 2.5-3.5 hours per side plus alignment (1 hour). Most shops do both sides together.
Estimated cost: $600-1,000 (both sides plus alignment)
Evaporator Core Leaks (A/C Failure)
Occasional · low severityTypical onset: 120,000-180,000 mi
Symptoms: A/C blows warm air, Sweet smell from vents, Oily residue on passenger floor or windshield, System won't hold refrigerant charge
Fix: Evaporator located behind the entire dashboard. Requires complete dash removal and HVAC box disassembly. Most labor-intensive job on this vehicle at 12-16 hours. Many owners live without A/C rather than repair.
Estimated cost: $1,800-2,800
Buy only with documented proof of frequent oil changes and recent radiator replacement; budget $5-8k reserve for inevitable engine or transmission work - the rest of the van is solid but these two issues are nearly unavoidable.
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.