Owners of 2005 Toyota Siennas report a cluster of engine and cooling system failures, each documented by specific mileages and repair attempts. The most frequent complaint involves radiators cracking at the plastic end cap and developing leaks, typically in cold weather, causing coolant loss and engine overheating. Mileages cited range from 54,000 to 104,000 miles. Several owners mention Toyota Technical Service Bulletin (TSB) notices acknowledging the defect but claim coverage limits excluded their vehicles.
Engine failures include a blown cylinder head at 5,000 miles since last oil change, producing oil smoke and risk of fire. A timing belt fracture occurred at 54,000 miles with no warning. One owner reported engine seizure requiring replacement at 142,000 miles after an oil warning light came on. Owners also describe engine knock/spark knock present since purchase that dealers couldn't resolve, and instances of spontaneous engine fires with no warning.
Air conditioning failures involve compressors cycling on and off, blowing hot air, and requiring repeated replacement. One dealer-quoted fix reached $4,000. Engine support failures caused rattling and abnormal motion at 60,000 miles. A heater core leak appeared at just 955 miles on a new vehicle.
Failure modes owners describe
Radiator cracking and coolant leaks
Plastic end cap cracks develop, typically in cold weather, causing rapid coolant loss and engine overheating. Occurs across multiple production batches despite Toyota's TSB (Jan 2006) claiming defect correction. Some owners excluded from warranty coverage based on production date or mileage thresholds.
When: 54,000–104,000 miles; cold weather onset; some as early as 955 miles on new vehicles
Symptoms owners cite: Visible coolant dripping or pooling; Engine overheating; Loss of coolant without visible external leak initially; Vehicle stalling or requiring emergency coolant top-up on roadside
Repairs/costs cited: Radiator replacement $200–$600+. Delayed parts availability (4+ days). One owner required cylinder head removal and milling ($2,000+) after radiator failure caused heat damage. Non-Toyota replacement parts sometimes incompatible with fitment.
Recalls/TSBs owners mention: Toyota TSB AC003-05 and TSB for cracking in cold weather; extended warranty offered with mileage limits (36,000 or 75,000 miles; vehicles over 7 years old denied). Toyota National Headquarters initially denied coverage claiming production was corrected, but some VINs still excluded. TSB acknowledged defect but limited coverage windows.
Blown cylinder head
Engine cylinder head developed a hole, allowing oil to escape, producing smoke visible from vehicle. Owner believes aluminum head was defective. Occurred 5,000 miles after oil service with no warning lights displayed.
When: 5,000 miles since last oil change (August 2012 service referenced)
Symptoms owners cite: Smoke emanating from hood and beneath vehicle; Long oil leak trail on street; Potential fire hazard noted by technician
Repairs/costs cited: Cylinder head replacement required. Risk of fire if driving continued.
Timing belt fracture
Timing belt broke suddenly at highway speed (70 mph) with no warning lights or symptoms beforehand. Vehicle lost power and could not exit roadway; law enforcement assisted pushing vehicle off road.
When: 54,000 miles
Symptoms owners cite: Sudden loss of engine power; No prior warning lights
Repairs/costs cited: Vehicle towed to repair shop for timing belt replacement. Full repair cost not specified.
Recalls/TSBs owners mention: Toyota declined to assist with repair costs.
A/C compressor failure and hot air discharge
Compressor cycles on and off erratically while blowing hot air from vents. Persists after compressor replacement. Eventually progresses to complete failure—compressor only blows hot air when A/C engaged.
When: Between 36,000 and 54,000+ miles in one case; failure reported April 2010; April 2012 in another
Symptoms owners cite: Hot air from driver-side vents despite A/C on; Compressor cycling on and off; Cold air gradually ceases
Repairs/costs cited: Compressor replacement twice in one vehicle (one owner). A/C pulley confirmed intact. Estimated repair cost $4,000 in one case. Another owner notes multiple previous recalls (rear door gas shocks, front driver door replacement).
Recalls/TSBs owners mention: Toyota TSB AC003-05 addresses issue but coverage capped at 36,000 miles. Failures beyond that threshold not covered.
Engine support failure
Engine mounting brackets or supports fail, causing engine to shift abnormally within engine bay and produce rattling noise on startup.
When: 60,000 miles
Symptoms owners cite: Rattling sound when starting engine; Abnormal motion felt in front of vehicle
Repairs/costs cited: Engine supports replacement required. Not repaired by owner; no cost cited.
Spontaneous engine fire
Engine caught fire spontaneously without warning, with vehicle parked and engine off. In one case, fire started at exhaust muffler area and spread into cabin.
When: December 5, 2007 (one documented); another during normal use
Symptoms owners cite: Fire visible in engine bay or exhaust area; No warning lights or symptoms prior to ignition
Repairs/costs cited: Fire department extinguished fire in one case. Vehicle status after fire not detailed.
Excessive engine spark knock
Chronic spark knock present since vehicle purchase (April 2005). Occurs at low speeds, during acceleration from stop, and at highway speeds under load. Worsens when engine is warm and during warm weather. Persists despite multiple dealer visits and octane adjustments.
When: Since purchase (April 2005); ongoing
Symptoms owners cite: Audible spark knock/pinging at low and high speeds; Worse when engine warm and during hot weather; Does not resolve with higher octane fuel
Repairs/costs cited: Multiple dealer visits attempted to resolve; no successful fix identified.
Engine requiring replacement
Engine failure requiring complete replacement. Owner noted oil warning light illuminated and added oil; subsequent inspection revealed engine needed replacement.
When: 142,000 miles
Symptoms owners cite: Oil warning light illumination
Repairs/costs cited: Engine replacement required. Vehicle towed to residence; not repaired by owner.
Brief unintended engine speed increases
Engine speeds up on its own for brief periods (few seconds), causing momentary vehicle acceleration without driver input.
When: Timing not specified
Symptoms owners cite: Brief engine revving; Unintended vehicle acceleration lasting seconds
Heater core leak
Rear heater core develops leak causing coolant to drip. Occurred at 955 miles on new vehicle. Persistent issue requiring multiple dealer visits totaling 15 days in shop.
When: 955 miles on new vehicle
Symptoms owners cite: Coolant dripping from rear heater core area
Repairs/costs cited: Heater core repair required. Multiple attempts (3+ visits) and 15 total days in dealer shop to resolve.
Synthesized from 25 NHTSA owner complaints — unverified consumer
allegations, summarized for patterns. The verbatim filings appear below.