The 2006 4Runner is a solid truck-based SUV, but the 4.0L V6 has a notorious piston slap issue and the 4.7L V8 can develop secondary air injection problems. Otherwise, rust on the frame and lower control arms are the major longevity concerns in salt states.
4.0L V6 Piston Slap (Cold Start Knock)
Common · medium severityTypical onset: starts early, often under 50,000 mi
Symptoms: Loud slapping/rattling noise for 30-60 seconds on cold starts, Disappears once engine warms up, No performance loss initially but can lead to accelerated cylinder wear
Fix: Toyota issued a TSB but no recall. Full fix requires short block replacement (20-25 hours labor). Most owners live with it since it doesn't typically cause immediate failure, but some see oil consumption increase after 150k mi.
Estimated cost: $4,500-7,000
4.7L V8 Secondary Air Injection System Failure
Common · low severityTypical onset: 80,000-150,000 mi
Symptoms: Check engine light with P0410, P0441, or P0446 codes, Air pump makes grinding noise or doesn't activate, Fails emissions testing in some states
Fix: Air pump, check valves, and hoses deteriorate. Pump replacement is 2-3 hours, but often the entire system needs refresh including valves and vacuum lines. Some states allow deletion if emissions testing doesn't require it.
Estimated cost: $800-1,800
Frame Rust (Particularly Rear Crossmember)
Common · high severitySymptoms: Surface rust on frame rails progressing to flaking and perforation, Rear crossmember near spare tire carrier especially vulnerable, Rear lower control arm mounts can rust through
Fix: Toyota had a frame replacement program that has expired. Mild cases can be treated with rust converter and POR-15 (8-12 hours prep and coating). Severe perforation requires welding in plates or section replacement (15-30 hours depending on extent). Inspect carefully before purchase in salt belt.
Estimated cost: $1,500-8,000
A750F 5-Speed Transmission Oil Cooler Lines Leak
Occasional · medium severityTypical onset: 100,000-180,000 mi
Symptoms: Pink/red fluid puddles under vehicle, Transmission fluid level drops, Harsh shifting or slipping if fluid gets low
Fix: Steel cooler lines rust at fittings or along length. Line replacement is 2-3 hours, but often includes replacing radiator if internal cooler is leaking into coolant. Always check for cross-contamination (strawberry milkshake of death).
Estimated cost: $400-1,200
Lower Ball Joint Wear
Common · medium severityTypical onset: 80,000-120,000 mi
Symptoms: Clunking over bumps, Loose or wandering steering feel, Excessive play detected during tire shake test
Fix: Lower ball joints are not serviceable separately on 4WD models—requires entire lower control arm replacement. 3-4 hours per side. Always do alignment after. Some aftermarket arms are garbage; stick with OEM or quality brands like Moog Problem Solver.
Estimated cost: $800-1,400
Radiator Plastic Tank Failure
Occasional · medium severityTypical onset: 120,000-180,000 mi
Symptoms: Coolant leak from side tanks (usually driver side), Overheating or temperature fluctuations, Pink residue at tank/core junction
Fix: OEM-style radiators with plastic tanks crack at crimps. Replace with quality all-aluminum unit if towing or off-roading. Job is straightforward, 2-3 hours including coolant flush. Do NOT use stop-leak products on these.
Estimated cost: $400-750
Evaporative System Charcoal Canister
Occasional · low severityTypical onset: 100,000+ mi
Symptoms: Check engine light with P0441 or P0446, Fuel smell near rear of vehicle, Difficulty fueling (pump clicks off repeatedly)
Fix: Charcoal canister saturates or purge valve sticks. Canister is behind fuel tank, 2-3 hours to drop tank and replace. Often confused with secondary air codes on V8 models, so proper diagnosis is critical.
Estimated cost: $500-900
Buy the 4.7L V8 if you can find one with no frame rust—it's more reliable long-term despite thirstier fuel consumption. Avoid high-mileage 4.0L V6 models with heavy piston slap unless you're okay with eventual short block replacement.
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.