According to Au7o's analysis of 8,800+ owner reports, the 1998 Mazda MX-5 Miata has 7 documented known issues, with 1 rated critical. The most serious is Rocker panel and front frame-rail rust (rear of rockers / behind front wheels) ($500-$4,000 repair). The most commonly reported issue is Soft Top Wear and Rear Window Delamination with 5,000 owner reports. Across all issues with published estimates, repair costs range from $80 to $4,000. DIY maintenance guides at au7o.io.
On the 1990-1999 Mazda MX-5 Miata, nA and NB Miatas are prone to structural rust in two well-known areas: the rear ends of the rocker panels (sills) and the front frame rails behind the front wheels. Road water enters through wheel-arch pinch welds and body seams and collects inside the double-layer sheet metal, rotting it from the inside out even when exterior paint looks fine. NB (1999+) frame rails are double-layer ('tinfoil sandwich') and rust worse than the single-layer NA rails. Salt-belt/winter cars are worst, but even garage-kept examples show rear-rocker rot. Because the rockers are structural on these unibody roadsters, advanced rot compromises chassis rigidity and safety.
Common Symptoms
Bubbling paint at the rear of the rocker panels
Flaking/perforated metal behind the front tires
Rust flakes visible in the sill drain holes
Soft/crunchy metal when probed at rockers or frame rails
Reduced chassis rigidity / cowl shake
How to Fix
Inspect carefully during purchase (probe the rear rockers and frame rails, don't just look). Small surface rust can be treated and sealed. Perforated rockers/frame rails require cutting out the rot and welding in replacement panels or reproduction rocker/rail sections (OEM NA single-layer rails preferred over NB double-layer). Add drain holes and cavity wax as prevention. Budget varies widely by severity and per side.
On the 1990-2025 Mazda MX-5 Miata, miata soft tops deteriorate over time from UV exposure, flexing during operation, and age. Vinyl tops develop cracks and tears, cloth tops fade and shrink. The rear plastic window (NA/NB) or glass window (NC/ND) can delaminate from the top material, causing water leaks and reduced visibility. Expected soft top life is 7-10 years with proper care.
Common Symptoms
Visible cracks or tears in top material
Rear window yellowing, hazing, or separating from fabric
Water leaks into cabin during rain
Top material shrinking and pulling away from frame
Difficulty latching top due to shrinkage
How to Fix
Replace soft top assembly. OEM replacement is available but aftermarket options (Robbins, TwinTop) offer better materials at lower cost. For NA/NB, replace rear window at same time. Apply 303 Aerospace Protectant or RaggTopp UV treatment every 3-6 months to maximize top life.
Owner tips & cautions
TipNever fold the top with a cold/stiff rear window (NA/NB) - causes permanent creases and cracks
TipDIY soft top replacement is doable in a weekend with Miata.net installation guide
High ConfidenceVerified5,000 owner reportsLast reported by owners Nov 2024Reviewed Feb 2026
On the 1990-1999 Mazda MX-5 Miata, nA and most early NB tops use a flexible plastic (vinyl) rear window, on many NA tops joined to the top with a zipper so the window can be lowered. With UV exposure and age the plastic yellows, hazes to near-opaque, and cracks (often starting at corners or the zipper seam); the zipper stitching tears out where the window meets the top. This is a near-universal age issue on unrestored cars and badly hurts rear visibility. A glass rear window with defroster was optional/standard on some later NB tops and does not haze, but zipper-window NA tops are the common case in this era.
Common Symptoms
Cloudy, yellowed, or opaque rear window
Cracks or splits in the plastic window
Window separating/tearing from the top at the zipper seam
Poor rearward visibility
How to Fix
Options scale with budget: DIY replace just the vinyl window panel for the lowest cost; have an upholstery shop transplant a new rear window (~$200-300 typical); or replace the entire soft top with a modern top that has a glass window and defroster. Note that aftermarket replacement windows use a non-standard zipper that will not mesh with the original Mazda zipper, so the original zipper often must be transferred to the new panel.
On the 1990-2015 Mazda MX-5 Miata, all generations of Miata (NA through NC) are prone to rear main seal leaks as the engine ages. Oil seeps from the crankshaft rear seal, dripping onto the clutch housing and eventually contaminating the clutch disc. High mileage engines and infrequent oil changes accelerate seal deterioration. This is a labor-intensive repair as the transmission must be removed.
Common Symptoms
Oil dripping from bell housing area (bottom of engine/transmission junction)
Oil smell when parked
Clutch slipping if oil contaminates clutch disc
Low oil level between changes
How to Fix
Replace rear main crankshaft seal. Since the transmission must be removed, replace the clutch, throwout bearing, and pilot bearing at the same time if they are worn. Clean bell housing thoroughly to remove oil contamination.
What you need to fix it
Only diagnosis- and fitment-reviewed repair parts are linked here.
Genuine Mazda BP05-11-312 rear main seal
OEMMazda BP05-11-312
Rear crankshaft seal after leak-source diagnosis for the corrected NA/NB branch Fitment/availability: The inspected direct OEM page lists BP05-11-312 as the rear crankshaft oil seal, replacing B630-11-312, for 1990-1997 and 1999-2005 Mia…
High ConfidenceVerified3,800 owner reportsLast reported by owners Oct 2024Reviewed Feb 2026
On the 1994-1999 Mazda MX-5 Miata 1.8L BP, on 1.8L BP engines, the Cam Angle Sensor (commonly called the CAS) mounts at the rear of the cylinder head, engaging the camshaft, and is sealed to the head by a single rubber O-ring. With age and heat cycling the O-ring hardens and shrinks, letting oil weep out of the back of the head. This is widely cited as the single most common oil-leak source on NA/NB Miatas; it typically fails before the valve-cover gasket. The oil runs down onto the nearby heater hoses (which it can rot) and the bellhousing. It is a nuisance leak rather than a failure, but a badly heat-soaked or oil-fouled CAS can also contribute to intermittent driveability faults.
Common Symptoms
Oil weep/drip at the rear of the cylinder head
Oil-soaked heater hoses near the firewall
Burning oil smell
Occasional heat-soak stall or hard restart when hot (severe cases)
How to Fix
Remove the CAS, discard the old O-ring, and install a fresh O-ring (a Viton -222 size is commonly used) lightly lubricated with clean oil; reindex the CAS to its factory alignment on reinstall so ignition timing is preserved. The part is a few dollars; most owners do it themselves. A shop visit is inexpensive. If a heat-soaked sensor is causing driveability faults, replace the CAS unit itself.
On the 1994-2000 Mazda MX-5 Miata, the 1994-2000 1.8L BP engines use a wasted-spark coil pack with an integrated igniter transistor. The early version (identified by the 4-pin input connector, later revised to 3-pin) is notorious for internal igniter/solder-joint failure, especially if the ignition is left in the ON position with the engine not running - the igniter transistor overheats and either burns out or melts its own solder connections. The result is a dead cylinder pair, a persistent misfire, and unburned fuel dumped into the catalytic converter.
Common Symptoms
Hesitation or stumble on startup that worsens over time
Severe misfire under load
Running rich, fuel smell, black smoke
Check engine light with misfire codes
Dead cylinder pair (1&4 or 2&3)
How to Fix
Replace the coil pack with an OEM Mazda unit (owners repeatedly report short life from budget aftermarket coils). Replace the plug wires and spark plugs at the same time since a failing coil stresses them, and inspect the catalytic converter if the car was driven while misfiring. Avoid leaving the key in ON without the engine running.
On the 1990-1999 Mazda MX-5 Miata, both the 1.6L B6 and 1.8L BP are belt-driven and Mazda specifies timing-belt replacement at 60,000 miles. On 25-35 year-old cars, belts frequently fail on age/dry-rot rather than mileage. The engines are non-interference, so a snapped belt will not bend valves, but it will strand the car. The water pump is driven behind the timing belt and commonly weeps or fails in the same 70k-170k window, so it is standard practice to replace the pump, tensioner, and seals while the belt is off since ~90% of the labor overlaps.
Common Symptoms
Engine cranks but will not start (belt failed)
Coolant weeping from the timing cover / under the crank pulley (water pump)
Ticking or squeal from the timing cover
Overheating from failed water pump
Cracked, glazed, or contaminated timing belt on inspection
How to Fix
Replace the timing belt on a strict time/mileage interval (every ~60k miles or when age/condition warrants) and do the water pump, tensioner spring, idler, front crank/cam seals, and accessory belts at the same time. Verify cam and crank timing marks on reassembly. DIY kits are affordable; shop labor is moderate.
What you need to fix it
Only diagnosis- and fitment-reviewed repair parts are linked here.
Treasure Coast Miata 1990-1993 premium Gates/Mazda timing-belt and water-pump kit
OEMTreasure Coast Miata 14385851 / TCM-0455
Complete timing-belt and water-pump service kit for the 1990-1993 1.6L branch Fitment/availability: The inspected direct page identifies SKU 14385851 for 1990-1993 Miata, requires selection around VIN 209445 and showed $271.50 with Add t…
Treasure Coast Miata 1994-2000 premium Gates/Mazda timing-belt and water-pump kit
OEMTreasure Coast Miata 18598700 / TCM-0519
Complete timing-belt and water-pump service kit for the corrected 1994-1997 and 1999 1.8L branches Fitment/availability: The inspected direct page identifies SKU 18598700 for 1994-2000 Miata, requires a year selection and showed $269.70 …
What are the most common Mazda MX-5 Miata problems?
According to Au7o's analysis of 8,800+ owner reports, the 1998 Mazda MX-5 Miata has 7 documented issues. The most frequently reported are: Rocker panel and front frame-rail rust (rear of rockers / behind front wheels), Soft Top Wear and Rear Window Delamination, Rear Main Seal Oil Leak. Of these, 1 is rated critical and should be addressed promptly.
Is the Mazda MX-5 Miata reliable?
The 1998 Mazda MX-5 Miata has 7 known issues documented across 8,800+ owner reports. 1 issue is rated critical: Rocker panel and front frame-rail rust (rear of rockers / behind front wheels). Prospective buyers should inspect for these issues and factor potential repair costs into their purchase decision. Regular maintenance following the manufacturer's schedule helps prevent many common problems.
How much does it cost to fix common Mazda MX-5 Miata problems?
Repair costs for known Mazda MX-5 Miata issues range from $80 to $4,000, depending on the specific problem and whether you choose DIY or professional repair. The most critical issue, Rocker panel and front frame-rail rust (rear of rockers / behind front wheels), typically costs $500-$4,000 to repair. Au7o provides step-by-step DIY maintenance guides that can help reduce repair costs.
What is the 1990-1999 Mazda MX-5 Miata Rocker panel and front frame-rail rust (rear of rockers / behind front wheels)?
NA and NB Miatas are prone to structural rust in two well-known areas: the rear ends of the rocker panels (sills) and the front frame rails behind the front wheels. Road water enters through wheel-arch pinch welds and body seams and collects inside the double-layer sheet metal, r… Repairs typically run $500-$4,000. Severity: high.
What is the 1990-2025 Mazda MX-5 Miata Soft Top Wear and Rear Window Delamination?
Miata soft tops deteriorate over time from UV exposure, flexing during operation, and age. Vinyl tops develop cracks and tears, cloth tops fade and shrink. The rear plastic window (NA/NB) or glass window (NC/ND) can delaminate from the top material, causing water leaks and reduce… Repairs typically run $300-$1,500. Severity: medium.
What is the 1990-2015 Mazda MX-5 Miata Rear Main Seal Oil Leak?
All generations of Miata (NA through NC) are prone to rear main seal leaks as the engine ages. Oil seeps from the crankshaft rear seal, dripping onto the clutch housing and eventually contaminating the clutch disc. High mileage engines and infrequent oil changes accelerate seal d… Repairs typically run $400-$1,200. Severity: medium.
What is the 1994-2000 Mazda MX-5 Miata Early 1.8L Coil Pack Internal Igniter Failure (4-Pin Connector Coils)?
The 1994-2000 1.8L BP engines use a wasted-spark coil pack with an integrated igniter transistor. The early version (identified by the 4-pin input connector, later revised to 3-pin) is notorious for internal igniter/solder-joint failure, especially if the ignition is left in the… Repairs typically run $90-$350. Severity: medium.
What is the 1990-1999 Mazda MX-5 Miata Overdue timing belt / water pump service (age-related, both engines)?
Both the 1.6L B6 and 1.8L BP are belt-driven and Mazda specifies timing-belt replacement at 60,000 miles. On 25-35 year-old cars, belts frequently fail on age/dry-rot rather than mileage. The engines are non-interference, so a snapped belt will not bend valves, but it will strand… Repairs typically run $350-$900. Severity: medium.
What is the 1990-1999 Mazda MX-5 Miata Convertible soft-top plastic rear window cracking, hazing, and zipper tear-out?
NA and most early NB tops use a flexible plastic (vinyl) rear window, on many NA tops joined to the top with a zipper so the window can be lowered. With UV exposure and age the plastic yellows, hazes to near-opaque, and cracks (often starting at corners or the zipper seam); the z… Repairs typically run $100-$700. Severity: low.
What is the 1994-1999 Mazda MX-5 Miata Cam/Crank Angle Sensor (CAS) O-ring oil leak on 1.8L engines?
On 1.8L BP engines, the Cam Angle Sensor (commonly called the CAS) mounts at the rear of the cylinder head, engaging the camshaft, and is sealed to the head by a single rubber O-ring. With age and heat cycling the O-ring hardens and shrinks, letting oil weep out of the back of th… Repairs typically run $80-$300. Severity: low.
Content on this page was compiled with AI assistance using NHTSA complaints, TSBs, owner reports, and public automotive data. While we strive for accuracy, this information may contain errors. Always verify repair procedures and specifications with your vehicle's service manual or a qualified mechanic.
