Toyota Supra (A70), Known Issues and Common Problems
Overview
The Toyota Supra A70 (1986-1993) is a well-engineered car let down by one critical design flaw in the 7M engine’s head gasket arrangement. Beyond that headline issue, the A70 is mechanically robust, Toyota built the chassis to a high standard, and most problems on these cars stem from age, neglect, or the consequences of poorly executed modifications.
These cars are now 33-40 years old. Many have been modified, some multiple times by different owners with different levels of skill. When diagnosing problems on an A70, always consider what has been changed from stock, the issue you’re chasing may be a modification side-effect rather than a factory deficiency.
Engine, 7M-GTE (Turbo)
Head Gasket Failure
What happens: The head gasket blows, allowing coolant into the combustion chambers and/or oil passages. White smoke from the exhaust, coolant loss without visible external leak, overheating under boost, milky oil on the filler cap, and bubbles in the coolant overflow tank. In severe cases, hydrolock (coolant filling a cylinder and bending a connecting rod on startup).
Why it happens: Toyota designed the 7M head with only 10 head bolts, insufficient clamping force for the cylinder pressures generated under boost. The factory composite head gasket degrades over time and eventually fails. Thermal cycling accelerates the process. Every 7M-GTE will eventually blow a head gasket on the factory bolts, it’s a matter of when, not if.
How to fix it: Strip the head, machine it flat (check for warpage, common after overheating), install a Cometic multi-layer steel (MLS) head gasket, and secure it with ARP head studs (part number 203-4205). The ARP studs provide dramatically more clamping force than the factory bolts. While the head is off, replace the valve stem seals. Retorque the studs to ARP’s specification (typically 85 ft-lb with ARP moly lube). Total cost: $1,500-2,500 including machining, gaskets, studs, and labour.
What doesn’t work: Simply re-gasketting with a standard gasket and factory bolts. It will fail again, usually within 20,000-50,000 km. Do not waste money on this approach.
Severity: Critical. This is an engine-killing failure if not caught early.
Low Oil Pressure at Idle
What happens: Oil pressure drops below 10 psi at hot idle. The factory oil pressure warning light may flicker or illuminate at idle, particularly in traffic on hot days. The engine may develop bearing noise (deep knocking from the bottom end).
Why it happens: The oil pump wears internally over time, reducing output at low RPM. The oil pressure relief valve spring weakens with age, allowing the valve to open too early and dump pressure back to the sump. Using incorrect oil viscosity (too thin) compounds the problem.
How to fix it: Start with an upgraded relief valve spring, this is a $30-50 part and a 30-minute job. It’s a bandaid but effective if the oil pump is only mildly worn. For a proper fix, replace the oil pump ($200-400 for the pump, plus labour to access it). An oil cooler relocation kit ($150-300) moves the oil cooler from the factory position to a more exposed location for better cooling, which helps maintain oil viscosity in hot conditions. Use 15W-40 or 10W-40 oil, do not use 5W-30 in a high-mileage 7M.
Severity: Urgent. Low oil pressure destroys bearings. If the light stays on at idle, stop driving immediately and investigate.
CT-26 Turbo Failure
What happens: Loss of boost pressure, excessive oil smoke (blue/grey) on startup or deceleration, whistling or grinding noises from the turbo, and oil in the intercooler piping.
Why it happens: The CT-26 has a limited service life. Shaft bearings wear, allowing the compressor and turbine wheels to contact their housings. Seal wear allows oil past the turbo seals into the intake (compressor side) or exhaust (turbine side). Running the turbo hard and shutting down immediately (no cool-down idle) accelerates seal and bearing failure.
How to fix it: Rebuild or replace. A CT-26 rebuild runs $400-800 at a turbo specialist. For anyone planning to increase power beyond stock, this is the time to upgrade. Common replacements: Garrett GTX3076R for mild builds (300-450 hp), BorgWarner S362 for mid-range (400-550 hp), Garrett GTX3582R for serious builds (500-700 hp). Upgrading from the CT-26 requires a new exhaust manifold (or adapter), oil and water lines, and an ECU retune. Budget $2,000-5,000 depending on the turbo choice.
Severity: Needs attention. A failing turbo won’t strand you immediately but will accelerate engine wear from oil consumption and reduced performance.
Cooling System Inadequacy Under Boost
What happens: Coolant temperature climbs rapidly under sustained boost, particularly in traffic or on hot days. The temperature gauge sits higher than normal and doesn’t recover quickly.
Why it happens: The factory radiator was adequate for 1986 driving conditions in Japan but struggles in Australian heat, particularly with any power increase. The fan clutch wears and stops driving the fan at sufficient speed. The intercooler and piping add heat to the engine bay.
How to fix it: Replace the radiator with an aluminium performance unit ($300-600), this is one of the highest-value modifications on a 7M-GTE car. Replace the fan clutch if it spins freely by hand when cold ($150-300), or convert to an electric fan setup with a quality controller ($300-600). Ensure the fan shroud is intact and properly sealed to the radiator, gaps allow air to bypass the radiator core.
Severity: Urgent in summer. Overheating causes head gasket failure, and the 7M is already vulnerable in that area.
Fan Clutch Wear
What happens: The engine runs hotter than normal, particularly at low speeds and idle. The cooling fan doesn’t seem to pull much air through the radiator.
Why it happens: The viscous fan clutch uses silicone fluid that leaks out over time as the internal seals wear. Once the fluid level drops, the clutch can’t engage fully and the fan freewheels.
How to fix it: With the engine cold, try to spin the fan by hand. A good fan clutch should have definite resistance, you shouldn’t be able to spin it easily. If it freewheels, replace it. Aisin or OEM Toyota units are preferred ($150-300). Alternatively, delete the clutch fan entirely and fit a quality electric fan with a thermostatically controlled relay ($300-600 for the conversion).
Severity: Needs attention. A failed fan clutch causes gradual overheating.
Engine, 7M-GE (Naturally Aspirated)
Head Gasket Failure (Less Common)
The 7M-GE shares the same head bolt design flaw as the turbo engine. However, without boost pressure stressing the gasket, failure is less frequent and less sudden. Symptoms are the same: coolant loss, white exhaust smoke, and overheating. The fix is the same: ARP studs and MLS gasket. The ARP stud upgrade is worthwhile as preventive maintenance on any 7M, even if the gasket hasn’t failed yet.
Severity: Important. Less urgent than on the turbo engine, but the same fundamental weakness exists.
Transmission
W58 Synchro Wear
What happens: Crunching or grinding when shifting into 2nd or 3rd gear, particularly when cold or during quick shifts. The synchros may improve slightly once the gearbox oil is warm.
Why it happens: The W58 is a light-duty gearbox with brass synchros that wear with age and aggressive use. The W58 was designed for the naturally aspirated 7M-GE and is marginal even at stock turbo torque levels. Anyone driving a modified turbo car through a W58 is on borrowed time.
How to fix it: A W58 rebuild with new synchros runs $800-1,500. However, if the car is making turbo power, the money is better spent swapping to an R154 ($1,500-3,000 for a complete swap including gearbox, bellhousing, tailshaft, and clutch). The R154 swap is one of the most well-documented modifications on the A70 platform.
Severity: Needs attention. Worn synchros are annoying and will eventually leave you unable to select gears.
R154 Input Shaft Bearing Noise
What happens: A whining or howling noise that changes when the clutch pedal is depressed. The noise is present in neutral with the clutch engaged and disappears when the pedal is pressed.
Why it happens: The input shaft bearing wears over time, particularly on cars that have been driven with heavy clutch setups or high power levels.
How to fix it: The bearing can be replaced without a full gearbox rebuild, but the gearbox must come out of the car. Budget $500-1,000 for the bearing replacement including removal and refitting the gearbox. While it’s out, inspect the synchros and replace the gearbox oil with a quality 75W-90 GL-4 fluid.
Severity: Needs attention. A failed input shaft bearing will eventually seize and destroy the gearbox.
Suspension and Chassis
Rear Subframe Cracking
What happens: Cracks develop in the rear subframe, typically around the differential mounting points and the subframe-to-body mounting brackets. May manifest as unusual handling, the rear end feeling “loose” or inconsistent over bumps.
Why it happens: High-mileage, hard driving, drag launches, and increased engine power all stress the rear subframe beyond its design limits. The factory subframe was designed for 200-230 hp, not 400+.
How to fix it: Inspect the subframe carefully, you need to get under the car on a hoist. Small cracks can be repaired by a qualified welder, but the subframe must be removed for proper access. Aftermarket reinforced subframes and subframe bracing kits are available ($500-1,500). For high-power builds, this is a preventive upgrade worth doing before cracks appear.
Severity: Critical. A cracked subframe is a structural and safety issue. Do not ignore this.
Spherical Bearing Wear in Suspension Arms
What happens: Clunking over bumps, imprecise steering response, uneven tyre wear. The car may feel vague at turn-in.
Why it happens: The A70 uses pressed spherical bearings (not rubber bushings) in the suspension arms. These are precision components that wear over time. The bearing surfaces corrode and develop play. This is often misdiagnosed by mechanics unfamiliar with the A70’s suspension design, they’ll suggest poly bushes as a “fix,” which actually makes the problem worse.
How to fix it: Replace the spherical bearings with correct OEM-spec replacements. This requires pressing out the old bearings and pressing in new ones. Specialty suppliers stock these, they’re not common hardware store items. Cost: $50-100 per bearing, plus pressing. Some aftermarket arms come with replaceable bearings for easier future maintenance.
What doesn’t work: Fitting polyurethane bushings in place of the spherical bearings. The suspension geometry was designed around the zero-deflection characteristics of spherical bearings. Poly bushes introduce unwanted compliance and change the handling characteristics.
Severity: Needs attention. Worn bearings compromise handling and cause tyre wear.
Body
Targa Roof Seal Deterioration
What happens: Water leaks into the cabin when it rains or when washing the car. Staining on the headliner, musty smell, and damp carpets. In severe cases, water collects in the footwells and causes corrosion of the floor pan and electrical connectors.
Why it happens: The rubber seals around the targa roof panel perish with age and UV exposure. The seal channels can also accumulate debris that prevents proper sealing. On cars that have sat for extended periods, the targa bolts can seize, making removal difficult and damaging the seal channel.
How to fix it: Replace the targa seals. Genuine Toyota seals are still available (check with a Toyota dealer, they’re surprisingly reasonable). Clean and lubricate the seal channels. If the targa bolts are seized, use penetrating oil over several days before attempting removal, forcing them will strip the threads in the body. New seal kits: $200-400 installed.
Severity: Needs attention. Water ingress causes corrosion and electrical faults.
Targa Bolt Seizure
What happens: The bolts that secure the targa roof panel to the body seize in place. Attempting to force them strips the threads or breaks the bolt heads.
Why it happens: Dissimilar metals (steel bolts in aluminium threads) combined with moisture create galvanic corrosion. Cars that sat for years without the targa being removed are worst affected.
How to fix it: Soak bolts in penetrating oil (Wurth Rost-Off or similar) for days, not hours. Apply gentle heat with a heat gun if accessible. If the bolt head strips, you’ll need to drill it out and helicoil the thread. Preventive measure: remove the targa panel twice a year, clean the bolts, and apply anti-seize compound on reassembly.
Severity: Minor but frustrating. Prevention is much easier than repair.
Pop-Up Headlight Motor Failure
What happens: One or both headlights fail to raise or lower, raise slowly, or raise unevenly. Clicking or grinding noise from the headlight motor area.
Why it happens: The electric motors and their nylon gearboxes wear over time. The gearbox teeth strip, or the motor itself fails electrically. Water ingress through worn seals accelerates failure.
How to fix it: The motor and gearbox assembly can be replaced as a unit. Toyota OEM parts are still listed but expensive ($200-400 per side). Aftermarket replacements are available and generally adequate. The motors can also be rebuilt by replacing the gearbox gears with aftermarket metal replacements ($50-100 DIY). Some owners convert to fixed headlights, but this changes the car’s appearance significantly.
Severity: Minor. The headlights still work manually (most can be raised by hand in an emergency).
Electrical
ABS Module Failure
What happens: The ABS warning light illuminates permanently. The ABS system may activate inappropriately (pulsing brake pedal during normal braking) or not function at all.
Why it happens: The ABS module on the A70 uses early electronic technology that degrades with age. Internal solder joints crack, capacitors fail, and the pump motor wears. The module is also sensitive to voltage spikes and poor grounds.
How to fix it: ABS module repair specialists can sometimes reboard the module ($300-600). Replacement modules are rare and expensive. Many owners disconnect the ABS system entirely and run without it, this restores normal braking but without anti-lock functionality. For cars that have had a manual transmission swap from an automatic, ABS integration issues are common because the speed sensor signals and wiring differ between auto and manual variants.
Severity: Needs attention. Non-functional ABS means the car relies solely on driver skill to prevent wheel lockup.
Power Steering Pump Whine
What happens: A persistent whining noise from the power steering pump, most noticeable at idle with the steering wheel centred (no load on the system).
Why it happens: Internal pump seals wear, allowing air to be drawn into the hydraulic fluid. The fluid becomes aerated, causing cavitation noise. Low fluid level from leaking hoses or rack seals worsens the issue.
How to fix it: Check and top up the power steering fluid first. Inspect all hoses and the steering rack for leaks. If the whine persists with correct fluid level and no leaks, the pump needs rebuilding or replacing ($300-500). Use genuine Toyota power steering fluid or a quality ATF, the wrong fluid accelerates seal wear.
Severity: Minor to needs attention. The pump will eventually fail completely if ignored, resulting in heavy steering.
Engine Wiring Harness Degradation
What happens: Intermittent electrical faults, random misfires, fluctuating idle, gauge malfunctions, check engine lights with inconsistent fault codes.
Why it happens: After 30+ years, the factory wiring harness insulation becomes brittle, particularly in the engine bay where it’s exposed to heat. Connectors corrode internally. On modified cars, spliced wiring from previous owners adds further failure points.
How to fix it: For a stock car, carefully inspect the harness, repair damaged sections, and clean all connectors with contact cleaner. Apply dielectric grease to connectors after cleaning. For modified cars with extensive wiring issues, a complete aftermarket engine harness from a specialist (e.g., Wiring Specialties) is the definitive solution ($500-1,500 for the harness, plus installation).
Severity: Varies. Can range from minor annoyance to complete no-start depending on which wires are affected.
Fuel System
Injector Failure/Inadequacy
What happens: Rough idle, misfiring under load, lean conditions (visible on wideband O2 gauge), and poor fuel economy.
Why it happens: On stock cars, the original injectors (260 cc on 7M-GTE) clog from age and contaminated fuel. On modified cars, the stock injectors are undersized for the increased airflow and can’t deliver enough fuel at high RPM/boost.
How to fix it: For stock engines, professional injector cleaning and flow testing is the first step ($15-20 per injector). If the injectors are beyond cleaning, replace with new OEM-spec units. For modified engines, common upgrades: 440 cc injectors for mild builds (up to ~350 hp), 550 cc RC Engineering injectors for moderate builds (350-500 hp), and 1,000 cc injectors for big-power builds. Any injector change requires a retune.
Severity: Needs attention. Lean running under boost destroys engines.
Preventive Maintenance
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Do the ARP head stud upgrade proactively on any 7M engine. Don’t wait for the gasket to fail, the cost is similar whether you do it preventively or after a failure, but a failed gasket can cause additional damage (warped head, scored cylinders).
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Change engine oil every 5,000-7,500 km using 15W-40 or 10W-40. Check oil pressure with a mechanical gauge, not the factory warning light.
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Replace the fan clutch if there’s any doubt about its condition. Overheating kills 7M engines.
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Inspect the rear subframe annually on any car making more than stock power. Cracks caught early are a weld repair; cracks caught late are a subframe replacement.
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Remove and re-grease the targa bolts twice a year. Five minutes of prevention saves hours of drilling out seized bolts.
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Use quality fuel. The 7M-GTE requires 98 RON for detonation resistance under boost. Do not run 91 RON in a turbocharged 7M.
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Let the turbo cool down before shutting off the engine. Idle for 60-90 seconds after spirited driving. A turbo timer is a cheap alternative ($50-100).
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