1991 FORD EXPLORER

Typical onset: 80,000-140,000 mi

Symptoms: White smoke from exhaust on cold start, Coolant loss with no visible leaks, Overheating under load or climbing grades, Milky oil or chocolate milk on dipstick, Rough idle and loss of power

Fix: Both heads off, resurface, new gaskets, timing cover re-seal. The OHV design makes removal easier than later SOHC engines, but book time is still 12-15 hours. Always check for warped heads—common on overheated motors. Budget for freeze plugs and intake gaskets while you're in there.

Estimated cost: $1,800-2,800

Typical onset: 60,000-120,000 mi

Symptoms: Red ATF puddles under front of vehicle, Transmission slipping or delayed engagement when fluid is low, Hissing sound near radiator area, Burnt ATF smell if driven while low

Fix: Steel cooler lines rust where they pass through the frame crossmember or connect to the radiator. Replace both lines as a set (3-4 hours labor). If lines failed and contaminated the trans with coolant (cracked radiator internal cooler), you're looking at a transmission rebuild or replacement. Always check radiator integrity during cooler line jobs.

Estimated cost: $400-700 for lines only; $1,500-2,500 if transmission is damaged

Typical onset: 90,000-150,000 mi

Symptoms: Slipping on 2-3 shift or no overdrive engagement, Delayed engagement into reverse, Grinding or whining noise in all gears, Burned ATF smell and dark/metallic fluid

Fix: The A4LD is a weak design behind the torquey 4.0L. Forward clutch pack failure is textbook at higher mileage. Rebuild runs 10-12 hours plus R&R time (total 16-20 hours). Many shops recommend upgrading to later 5R55E if doing a swap, but that requires controller modifications. Budget rebuild with updated clutches and bands is the typical path.

Estimated cost: $1,800-3,200

Typical onset: 70,000-130,000 mi

Symptoms: Oil seepage or drips from front of engine, Oil pooling on crossmember or front differential, Oil smell in cabin after highway driving, Visible oil coating on harmonic balancer

Fix: The timing cover gasket and front main seal on the Cologne V6 leak as the rubber hardens. Not catastrophic but messy and wasteful. Repair requires pulling accessories, damper, and timing cover (8-10 hours). Water pump is behind the timing cover—replace it at the same time or you'll be back in six months. This is preventive bundling that pays off.

Estimated cost: $900-1,400

Symptoms: Fuel smell inside cabin or around rear of vehicle, Visible rust perforation on filler neck tube, Difficulty inserting fuel nozzle or slow fill at pump, Check engine light with EVAP codes

Fix: Salt belt Explorers eat filler necks from the outside in. The neck rusts through where it connects to the tank or along the tube run. Replace the entire filler neck assembly (2-3 hours labor). Early 1991s also had a recall for tank strap corrosion—inspect straps during any fuel system work.

Estimated cost: $300-550

Typical onset: 80,000-120,000 mi

Symptoms: Clunking over bumps or during turns, Loose or wandering steering feel, Uneven tire wear on inside or outside edges, Excessive play when checking wheel at 12 and 6 o'clock

Fix: Twin I-Beam front suspension uses both upper and lower ball joints that wear from age and road salt. Lower ball joints fail more frequently. Both uppers and lowers should be replaced as pairs per side (4-6 hours for both sides). Alignment mandatory afterward. The I-Beam design is tough but parts are wear items.

Estimated cost: $600-1,000 for both sides