1991 MAZDA B2600

Typical onset: 120,000-180,000 mi

Symptoms: Heavy knocking on cold start that worsens with RPM, Metallic ticking that becomes a loud hammering under load, Sudden oil pressure drop, Metal shavings in oil filter or pan

Fix: The 2.6L G54B is notorious for spinning rod and main bearings, especially cylinder #3. Requires full teardown, crank machining or replacement, new bearings, often new pistons and rings. Machine shop work adds 1-2 weeks. Total labor 18-24 hours if reusing block, 22-28 hours for short-block swap.

Estimated cost: $2,800-5,200

Typical onset: 90,000-140,000 mi

Symptoms: White smoke from exhaust on cold start, Coolant loss with no visible leaks, Bubbling in overflow tank at idle, Rough idle and misfires, Oil that looks milky or foamy

Fix: The G54B runs hot and blows head gaskets between cylinders 2-3. Head must be checked for warpage and often requires machining. While head is off, smart shops replace timing chain guides and water pump. Labor 10-14 hours for gasket job, add 2-3 hours if head needs surfacing.

Estimated cost: $1,200-2,400

Symptoms: Stumbling on acceleration, Black smoke and fuel smell at idle, High idle that won't drop, Stalling when warm, Failed emissions tests

Fix: The feedback carburetor uses O2 sensor, computer control, and multiple vacuum solenoids that all fail independently. Parts are discontinued OEM; aftermarket quality is hit-or-miss. Diagnosis is tedious—3-5 hours to chase vacuum leaks, test solenoids, verify O2 function. Carb rebuild kits run $80-150, but full carb replacement with reman unit is often cheaper long-term at 4-6 hours labor.

Estimated cost: $450-1,100

Typical onset: 100,000-150,000 mi

Symptoms: ATF dripping near radiator or under truck, Low transmission fluid with no pan leak, Transmission slipping or delayed engagement, Pink or milky fluid in coolant overflow

Fix: Steel hard-lines from transmission to radiator corrode where they clip to frame. If cooler inside radiator fails, ATF mixes with coolant and kills the transmission within days. Line replacement is 2-3 hours, but catching it late means transmission rebuild. If cross-contamination occurred, flush cooling system and replace radiator.

Estimated cost: $280-650

Symptoms: Visible rust through on rear frame rails behind cab, Bed shifting or sagging on one side, Holes in frame where bed bolts mount, Failed state inspections in rust-belt states

Fix: Mazda B-series frames rust from inside-out, especially rear crossmember and bed mount points. Surface rust becomes structural failure quickly. Repair requires cutting out bad sections and welding in new steel—8-12 hours if localized, but many trucks are totaled when multiple areas are compromised. Pre-purchase inspection with a wire brush is critical.

Estimated cost: $800-2,500

Typical onset: 130,000-180,000 mi

Symptoms: Rattling on cold start that fades after 10-20 seconds, Metallic chatter from front of engine at idle, Check engine light with cam/crank correlation codes on late models

Fix: Plastic timing chain guides crack and tensioners lose pressure. Chain itself rarely fails but can jump time if guides disintegrate. Requires front cover removal and water pump access—8-10 hours labor. Always done during head gasket jobs to avoid repeat teardown.

Estimated cost: $650-1,200