Which parts fail
Components named in complaints (engine, cooling system, oil leaks, timing chain, exhaust).
Mileage when the problem started
Owner reports
Selected complaints filed with NHTSA by 1998 Mercury Mountaineer owners, lightly cleaned up (personal details are redacted by NHTSA).
One of the braided stainless steel fuel lines that attaches to the engines fuel rail developed a leak. I kept smelling a strong odor of gas, but I could not find out where it was coming from. After two weeks of smelling the gas, I took it to a garage and they showed me the gas squirting from the braided hose going to the engine. I took the vehicle to the Ford dealer and showed them the leak. They took the vehicle in their shop and removed the fuel lines. Because of the age of the vehicle, Ford does not provide any replacement parts. I was unable to get replacement fuel lines from Ford. I checked with "junk yards" all over the country. I had no luck finding replacement fuel lines. Junk yards cut the fuel line when they pull engines. I finally located a company in new castle, de that supplies hydraulic hoses, etc. …
When the 1998 Mercury Mountaineer was running on hwy 121 south merging into hwy 114 west in grapevine, tx, the 1998 Mercury suddenly became out of control at a speed less than speed limit. The car was being accelerated even if the accelerator pedal was off. The driver applied break to stop the car but the break did not work. Then the driver had to steer the car into the bush off road to avoid collision to other cars. The driver changed the at to p (parking) to stop the car. The engine surged and started fire underneath of the car. Then the driver removed the key and evacuated from the car. The fire was extinguished by the fireman.
Dt*: the contact stated a fire erupted from the vehicle. It was parked for over thirty minutes. No previous problems were reported with the vehicle. The fire department was called to the scene to extinguish the fire. The fire investigator's written report stated the fire started in the engine compartment. There was additional property damage to surrounding vehicles. The insurance company inspected the vehicle and deemed it totaled.
At 2 am we smelled smoke and saw it coming from garage, when I opened garage door flames were coming out of front of car. My mothers car burnt and it is a total loss. We had to call fire dept. My garage was wrecked. My house has smoke damage.
My check engine light has been coming on. I have had various shops use their computer to find out why the light was on and have paid for cleaning valves, sensors, and hoses as well as having new sensors installed. The first instance occurred at 65, 475 mileage on my vehicle. Today, the shop where I now take my vehicle for servicing used their computer to see why the check engine light was on yet again and it generated a TSB from Ford, article 04-7-5 which supersedes article TSB 03-25-1. This article states the issue as "some 1998 explorer/Mountaineer vehicles equipped with the 5.0l engine May exhibit a malfunction indicator lamp (MIL) on with diagnostic trouble code(s) p0420 (catalyst system efficiency below threshold-bank 1) and/or p0430 (catalyst system efficiency below threshol - bank 2). …
Tl contact owns a 1998 Mercury Mountaineer. Early in the morning, the contact smelled something burning and noticed that her vehicle was on fire. As a result, the garage and part of the house were burned. The fire department extinguished the fire and stated that it originated from the engine of the vehicle. The contact feels that this is a safety issue because severe injuries could have occurred. The mileages were unknown.
Tl contact owns a 1998 Mercury Mountaineer. The contact stated that there is a crack in the center of the EGR valve. The vehicle is making an unfamiliar noise and gas fumes are entering the vehicle. There were no warning indicators. The vehicle has not been diagnosed. The purchase date, engine size, and a valid VIN were unknown. The current mileage is 72,000 and failure mileage was 69,000.
Ford refuses to honor extended warranty, program # 01m01 on 1998 Mountaineer; VIN [redacted], " any other engine damage clearly resulting from a worn or broken front cam chain guide is also covered"! Rear cassette bad, engine needed to be replaced at my cost. Updated 07/30/2012
Drove vehicle and parked it, had no warning signs, about 5 minutes, vehicle exploded and caught on fire in the engine compartment. The vehicle was totaled. Aaa inspected vehicle, and said it was a defect in the engine. Please provide further information.
Ford motor company mr. Mike mcmullin district manager August 29,2005 dear sir, I purchased a 1998 Mercury 5.0l Mountaineer in July 1999 and it currently has some 85,000 miles on it. Long before the 36-month/36K miles warranty ran out, I complained to my Ford dealer that I heard an engine noise that sounds something like a hydraulic valve lifter sticking. In taking my car into an independent service center lately for some non-warranty minor service work, the mechanic there asked me how long I had been experiencing the engine noise that his trained ear was hearing. I informed him that it had been clicking like that for a good long time. Just for curiosity he checked the NHTSA web site for technical service bulletins (tsbs). …
NHTSA investigations
Spark plug ejection from cylinder head
On September 6, 2005, odi received a petition requesting that the agency investigate allegations of engine spark plug ejection in certain model year 1997 through 2004 Ford vehicles with triton v-8 and v-10 engines.odi received a total of 474 non-duplicative complaints on the subject vehicles where the complainant, or the dealer repairing the vehicle, reported that a spark plug detached from the cylinder and/or…
Engine complaints in other Mountaineer years
Frequently asked questions
How common are engine problems on the 1998 Mercury Mountaineer?
NHTSA has 22 complaints about the engine & cooling of the 1998 Mercury Mountaineer, 9% of the model year's 236 complaints. The component named most often is engine (9 mentions).
Is there a recall for 1998 Mercury Mountaineer engine problems?
No. NHTSA lists no engine & cooling recall for the 1998 Mercury Mountaineer, though it has 5 recalls for other components. If the problem is widespread, a repair may still be covered by an extended warranty or a manufacturer service bulletin — ask a dealer.
At what mileage do 1998 Mercury Mountaineer engine problems start?
Half of the complaints with a recorded mileage happened before about 72,000 miles, and 9% before 25,000 miles.
Is it dangerous?
Owners linked 1 crash, 7 fires and 1 injury to engine & cooling problems on this model year. If you notice symptoms, have the car checked before driving further.
Source: U.S. National Highway Traffic Safety Administration (NHTSA) — owner complaints through October 20, 2026, recalls and defect investigations; fuel economy from the EPA. Complaints are unverified reports and are not proof of a defect. How we rate model years.