The 1998 Expedition is a body-on-frame workhorse that can rack up miles, but the Triton V8s have a notorious spark plug issue and both engine options face intake manifold failures. The 4R70W transmission is generally solid but runs hot when towing, and the rear suspension sees frequent failures from the weight and use profile.
Spark Plug Ejection / Blown-Out Threads (4.6L and 5.4L)
Common · high severityTypical onset: 60,000-150,000 mi
Symptoms: sudden loud popping or hissing noise from engine bay, immediate misfire and rough idle, CEL with misfire codes, loss of power
Fix: The two-piece spark plugs break on removal, and the aluminum heads strip threads. If caught early, HeliCoil inserts work (2-3 hours per hole). If a plug blows out while driving, you're looking at head removal and TimeSert inserts, or worst case, replacement heads. Budget 8-12 hours labor for a full head-off repair on one bank.
Estimated cost: $500-2,500
Intake Manifold Gasket Failure (4.6L and 5.4L)
Common · medium severityTypical onset: 80,000-120,000 mi
Symptoms: coolant loss with no visible external leaks, white smoke from exhaust on cold start, rough idle when warm, coolant in oil (milky dipstick) in severe cases
Fix: The plastic intake manifolds crack internally or the composite gaskets fail, allowing coolant into the intake runners or oil passages. Requires manifold removal and gasket replacement, often includes new thermostat housing while you're in there. 6-8 hours labor.
Estimated cost: $800-1,400
Transmission Cooler Line Failure at Radiator
Common · high severitySymptoms: transmission fluid pooling under front of vehicle, pink fluid in coolant reservoir (transmission fluid mixing with coolant), transmission slipping or delayed engagement, rapid overheating of transmission
Fix: The factory quick-connect fittings at the radiator corrode and fail, or the internal transmission cooler ruptures, mixing ATF and coolant. If caught immediately, you replace lines and flush both systems (3-4 hours). If fluids mixed, the transmission is toast—needs full rebuild or replacement (12-16 hours labor for R&R plus rebuild).
Estimated cost: $300-4,500
Rear Axle Pinion Seal and Bearing Failure
Occasional · medium severityTypical onset: 100,000-180,000 mi
Symptoms: gear oil leak at front of rear differential, whining or howling from rear end that changes with speed, clunking on acceleration, vibration at highway speeds
Fix: The pinion seal leaks first, then the bearing goes if you keep driving on it. Seal replacement alone is 2-3 hours, but if the bearing is shot, you need to set pinion depth and preload, which bumps it to 4-6 hours. Often find the ring and pinion need replacement too if run low on oil.
Estimated cost: $400-1,800
Upper and Lower Ball Joint Failure
Common · high severityTypical onset: 80,000-140,000 mi
Symptoms: clunking over bumps from front end, wandering or loose steering, uneven tire wear on inside or outside edges, front end shimmy at highway speeds, visible play in wheel when jacked up
Fix: These trucks eat ball joints, especially uppers. The boots tear, dirt gets in, and they wear out fast. Uppers and lowers should be done together. The uppers require pressing out rivets or cutting them off, then bolting in new ones. Figure 4-6 hours for both sides, all four joints.
Estimated cost: $800-1,200
Fuel Pump Failure
Occasional · high severityTypical onset: 120,000-180,000 mi
Symptoms: no-start with plenty of cranking, stalling at operating temperature, loss of power under load or at highway speeds, whining noise from rear of vehicle, long crank times before starting
Fix: The in-tank pump fails from age and heat cycling. Requires dropping the 30-gallon fuel tank (easier said than done when it's got 20 gallons in it). 3-4 hours labor. The sending unit often fails at the same time, so replace both if you're in there.
Estimated cost: $600-900
Rear Air Suspension Failure (if equipped)
Common · low severityTypical onset: 60,000-100,000 mi
Symptoms: rear end sagging, especially when loaded, compressor running constantly, suspension warning light, inability to level with load
Fix: The air springs crack and leak, and the compressor wears out from overwork. Most owners convert to conventional coil springs (2-3 hours). If you want to keep it stock, new air springs and compressor run 4-5 hours labor, but expect to do it again in another 60k.
Estimated cost: $400-1,500
Buy one if it's been meticulously maintained with records showing spark plugs, trans cooler lines, and ball joints addressed—otherwise, budget $3,000-5,000 for catch-up repairs in the first year.
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.