According to Au7o's research across NHTSA recalls, manufacturer TSBs, and owner forum reports, the 1973 Datsun 240Z has 7 documented known issues, with 3 rated critical. The most serious are Unibody Rust: Frame Rails, Floor Pans, Battery Tray & Doglegs ($1,500-$12,000 repair), L24 Flat-Tappet Cam Wear & Brass Valve Seats on Modern Fuel/Oil ($200-$2,500 repair) and Marginal Cooling System & L24 Overheating ($400-$1,800 repair). Across all issues with published estimates, repair costs range from $150 to $12,000. DIY maintenance guides at au7o.io.
On the 1970-1973 Datsun 240Z L24 inline-6, the S30 240Z left the factory with minimal rustproofing and several built-in moisture traps, so rust is the single biggest weak point restorers face. Corrosion attacks the structural front frame rails, the floorpans, the battery tray (acid + trapped water accelerate it), the rear 'dogleg' below the quarter window, the rocker panels, the spare-tire well, the cowl (water drains through it and rots from the inside out), and around the hatch. Because the 240Z is a unibody with no separate chassis, the frame rails and floors ARE the structure — a rotten rail means the car flexes, doors no longer shut, and suspension/diff mounting points lose their integrity. Most failed 240Z projects fail not from visible surface rust but from hidden structural rot the buyer never checked.
Common Symptoms
Bubbling or flaking paint along rockers, fenders and doglegs
Soft or holed floorpans found when lifting the carpet
Rusted-through battery tray with green corrosion
Doors that sag or won't latch (shell has lost rigidity)
Water leaks / damp carpet from rotted cowl and hatch seals
Flaking metal in the spare-tire well
How to Fix
Bulletproof it with full reproduction steel rather than patching: weld in repair panels that are now reproduced for nearly every rot area (full and half floorpans, frame-rail sections, battery tray, dogleg and rocker repair panels, spare-well). Media-blast or chemically strip the shell to find ALL the rust first, butt-weld new metal (not lap/overlap), then seal welds with weld-through primer, epoxy prime, and critically pump cavity wax (e.g. Fluid Film / Eastwood Internal Frame Coating) into the frame rails, rockers and box sections so it never returns. Drill/clear the factory cowl and rocker drains, and re-seal the battery tray (or relocate the battery) to stop the most common re-rot point.
On the 1970-1973 Datsun 240Z L24 inline-6, the L24 uses a flat-tappet (sliding-contact) overhead camshaft riding directly on rocker arms — a design that depends on the high ZDDP (zinc/phosphorus) levels of 1970s oil. Modern low-ZDDP, emissions-friendly oils don't provide enough anti-wear film, so a freshly rebuilt or hard-running L24 can 'wipe' a cam lobe and rapidly destroy the camshaft and rockers — a classic, expensive restoration heartbreak. Compounding it, the early E31/E88 heads use softer BRASS exhaust valve seats designed for leaded fuel; on today's unleaded they erode and recede, dropping compression and burning valves.
Common Symptoms
Tapping/clatter from the head, rough idle (worn cam lobe)
Power loss and a wiped/rounded lobe found at valve adjustment
Low or dropping compression on one or more cylinders
Metallic glitter in the oil after a fresh rebuild
How to Fix
Bulletproof the valvetrain in two parts. First, run a proper high-ZDDP oil (a dedicated classic/flat-tappet oil at ~1,200-1,500 ppm zinc) and, on any rebuild or new cam, do a strict break-in with assembly lube + a high-zinc break-in oil so the lobes properly mate. Keep the oil-spray-bar/lubrication path clear during the rebuild. Second, when the head is off, have a machine shop install hardened, unleaded-compatible exhaust valve seats (and fresh guides/valves) so it tolerates pump gas indefinitely. Together these stop the two most common L24 top-end failure modes.
On the 1970-1973 Datsun 240Z L24 inline-6, the L24's factory cooling system is marginal by modern standards, and 50 years of scale, aging brass/copper radiators, tired water pumps, clogged passages and a sludged block leave many 240Zs prone to overheating — especially in traffic, in hot climates, or with any performance build. The stock dash temp gauge is also imprecise, so owners often don't realize how hot the engine actually runs. Chronic overheating on an L-series risks a blown head gasket and, worse, a cracked cylinder head — exactly what a restorer is trying to avoid.
Common Symptoms
Temp gauge climbing in traffic or on hot days
Coolant loss, pinhole radiator leaks or boil-over
Heat soak / hard hot restarts (carb percolation)
Overflow puking after shutdown
Head gasket failure or cracked head if neglected
How to Fix
Bulletproof the cooling system as a package: fit a high-efficiency aluminum radiator (or a quality re-cored brass unit with more rows) with a proper fan shroud, add a thermostatically-controlled electric fan to kill heat soak in traffic, and renew the water pump, a correct-temp thermostat, and silicone hoses. Back-flush the block to clear decades of scale (or hot-tank it during a rebuild), use a good coolant + water-wetter, and verify real temps with a mechanical/aftermarket gauge rather than trusting the stock one. This combination keeps street and mildly-built L24s cool and protects the head from cracking.
On the 1970-1973 Datsun 240Z L24 inline-6, after 50 years every rubber bushing and mount on a 240Z is hardened, cracked or collapsed — control-arm and tension-rod (T/C) bushings, sway-bar bushings, the transverse-link mounts, plus the R180 differential front mount and 'mustache-bar' rear diff insulators and the transmission mount. Worn T/C and diff/mustache-bar bushings let the geometry wander under load and produce the classic 240Z driveline 'clunk' on acceleration and shifts, vague steering, and uneven tire wear. The mounts also let the differential move, stressing the diff and the body mounting points.
Common Symptoms
Driveline 'clunk' on acceleration, deceleration and shifts
Vague, wandering steering and poor turn-in
Clunks/rattles over bumps from worn T/C and link bushings
Uneven/feathered tire wear and bouncy ride
Visible cracked, collapsed or oil-soaked rubber bushings
How to Fix
Refresh the entire suspension and driveline-mount package while the car is apart. Restorers fit polyurethane bushing kits throughout (control arms, T/C rods, sway bar) for sharper, longer-lasting handling, renew the R180 differential front mount and the mustache-bar/diff insulators (poly or fresh OEM-style) plus the transmission mount to kill the driveline clunk, and replace the tired shocks/struts with quality gas inserts (often with lowering/uprated springs). Many also add a urethane or reinforced mustache bar so the diff is properly located. The result is tight, modern-feeling handling and a clunk-free driveline.
On the 1970-1973 Datsun 240Z L24 inline-6, the 240Z uses front discs but REAR DRUM brakes, and after decades of sitting the whole system is usually tired: the rear drums fade with repeated/heavy use, the wheel cylinders leak, the single-circuit-era hardware and rubber hoses are perished, and the proportioning is dated. For a restored Z that actually gets driven hard (or has more power), the rear drums are the weak link in braking balance and consistency.
Uneven braking or rear lockup from worn drum hardware
Poor parking-brake hold
How to Fix
The proven upgrade is a rear disc conversion — bolt-on kits use later Datsun/Maxima or Toyota calipers/rotors that mount to the stock locations (with an integrated parking-brake), requiring 15-inch-or-larger wheels for caliper clearance. Many restorers pair it with a front upgrade (e.g. Toyota 4Runner/300ZX 4-piston caliper + vented rotor swap), stainless braided brake lines for a firm pedal, fresh DOT4 fluid, and a correctly-sized master cylinder/proportioning to balance the new discs. The result is consistent, fade-free, modern stopping that matches a uprated drivetrain.
On the 1970-1973 Datsun 240Z L24 inline-6, the 240Z left the factory with only a ~40-amp alternator and a crude points-type EXTERNAL mechanical voltage regulator. The mechanical regulator can't hold a stable output by modern standards, its contacts pit and stick with age, and it commonly causes under- or over-charging, flickering lights and dead batteries. The low 40A output also can't comfortably support electric cooling fans, halogen lighting, an electric fuel pump or a modern stereo — all common upgrades on a restored Z.
Common Symptoms
Dim or flickering headlights, fluctuating ammeter
Battery repeatedly going flat or boiling/overcharging
Charging that drops out then returns (sticking regulator points)
Electrical accessories browning out at idle
Burnt or corroded voltage-regulator connector
How to Fix
Convert to a modern internally-regulated alternator. The favorite swap is the 60A unit from an 81-83 280ZX, which bolts directly to the L24 block; pair it with a plug-in conversion adapter (with the required diode built in) so no harness wiring is cut and the change stays fully reversible. This deletes the troublesome external regulator entirely, delivers a steady 13.8-14.7V, and provides headroom for electric fans and accessories. While in the engine bay, restorers also clean/upgrade the battery and ground cables and refresh the fusible-link/fuse connections that corrode and cause phantom electrical gremlins.
On the 1973 Datsun 240Z L24 inline-6, for the 1973 model year (emissions-era), Datsun switched the twin Hitachi SU carbs from the proven HJC46W 'round-top' design to the HMB46W 'flat-top' with an integrated (HIF-style) float chamber. These flat-tops are notoriously hard to tune, far less reliable than the round-tops, run rich/lean as the throttle shafts and worn float systems age, and are loaded with emissions-era vacuum complications. On a restoration they cause hard starting, poor idle, stumbling and dismal economy, and good rebuildable cores plus knowledgeable rebuilders for them are scarce.
Common Symptoms
Hard cold starting and erratic idle
Hesitation/stumble off idle and flat spots
Poor fuel economy and fouled plugs (running rich)
Carbs that won't stay in balance/tune
Fuel smell from leaking integrated float chambers
How to Fix
The community-proven fix is to ditch the flat-tops and bolt on the earlier round-top HJC46W SUs (1970-72 240Z spec) — they share the manifold and linkage, tune easily, and parts/kits are plentiful. Best practice is to fit a professionally restored/bushed set (ZTherapy or equivalent) so the throttle shafts aren't worn, then balance with a Unisyn and set mixture with the float/nozzle method. Many builders also delete the leftover emissions vacuum plumbing during the swap. Those wanting modern reliability instead fit triple Mikuni/Weber sidedrafts or an EFI conversion, but round-top SUs keep it period-correct and dependable.
According to Au7o's research across NHTSA recalls, manufacturer TSBs, and owner forum reports, the 1973 Datsun 240Z has 7 documented issues. The most frequently reported are: Unibody Rust: Frame Rails, Floor Pans, Battery Tray & Doglegs, L24 Flat-Tappet Cam Wear & Brass Valve Seats on Modern Fuel/Oil, Marginal Cooling System & L24 Overheating. Of these, 3 are rated critical and should be addressed promptly.
Is the Datsun 240Z reliable?
The 1973 Datsun 240Z has 7 known issues compiled from NHTSA recalls, manufacturer TSBs, and owner forum reports. 3 issues are rated critical: Unibody Rust: Frame Rails, Floor Pans, Battery Tray & Doglegs and L24 Flat-Tappet Cam Wear & Brass Valve Seats on Modern Fuel/Oil and Marginal Cooling System & L24 Overheating. 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 Datsun 240Z problems?
Repair costs for known Datsun 240Z issues range from $150 to $12,000, depending on the specific problem and whether you choose DIY or professional repair. The most critical issue, Unibody Rust: Frame Rails, Floor Pans, Battery Tray & Doglegs, typically costs $1,500-$12,000 to repair. Au7o provides step-by-step DIY maintenance guides that can help reduce repair costs.
What is the 1970-1973 Datsun 240Z Unibody Rust: Frame Rails, Floor Pans, Battery Tray & Doglegs?
The S30 240Z left the factory with minimal rustproofing and several built-in moisture traps, so rust is the single biggest weak point restorers face. Corrosion attacks the structural front frame rails, the floorpans, the battery tray (acid + trapped water accelerate it), the rear… Repairs typically run $1,500-$12,000. Severity: high.
What is the 1970-1973 Datsun 240Z L24 Flat-Tappet Cam Wear & Brass Valve Seats on Modern Fuel/Oil?
The L24 uses a flat-tappet (sliding-contact) overhead camshaft riding directly on rocker arms — a design that depends on the high ZDDP (zinc/phosphorus) levels of 1970s oil. Modern low-ZDDP, emissions-friendly oils don't provide enough anti-wear film, so a freshly rebuilt or hard… Repairs typically run $200-$2,500. Severity: high.
What is the 1970-1973 Datsun 240Z Marginal Cooling System & L24 Overheating?
The L24's factory cooling system is marginal by modern standards, and 50 years of scale, aging brass/copper radiators, tired water pumps, clogged passages and a sludged block leave many 240Zs prone to overheating — especially in traffic, in hot climates, or with any performance b… Repairs typically run $400-$1,800. Severity: high.
What is the 1970-1973 Datsun 240Z Perished Suspension Bushings & Differential/Mustache-Bar Mounts?
After 50 years every rubber bushing and mount on a 240Z is hardened, cracked or collapsed — control-arm and tension-rod (T/C) bushings, sway-bar bushings, the transverse-link mounts, plus the R180 differential front mount and 'mustache-bar' rear diff insulators and the transmissi… Repairs typically run $300-$1,500. Severity: medium.
What is the 1970-1973 Datsun 240Z Outdated Rear Drum Brakes (Disc Conversion Candidate)?
The 240Z uses front discs but REAR DRUM brakes, and after decades of sitting the whole system is usually tired: the rear drums fade with repeated/heavy use, the wheel cylinders leak, the single-circuit-era hardware and rubber hoses are perished, and the proportioning is dated. Fo… Repairs typically run $500-$2,500. Severity: medium.
What is the 1970-1973 Datsun 240Z Weak 40A Alternator & Failure-Prone External Voltage Regulator?
The 240Z left the factory with only a ~40-amp alternator and a crude points-type EXTERNAL mechanical voltage regulator. The mechanical regulator can't hold a stable output by modern standards, its contacts pit and stick with age, and it commonly causes under- or over-charging, fl… Repairs typically run $150-$450. Severity: medium.
What is the 1973 Datsun 240Z Troublesome '73 Flat-Top Hitachi SU Carburetors?
For the 1973 model year (emissions-era), Datsun switched the twin Hitachi SU carbs from the proven HJC46W 'round-top' design to the HMB46W 'flat-top' with an integrated (HIF-style) float chamber. These flat-tops are notoriously hard to tune, far less reliable than the round-tops,… Repairs typically run $400-$1,500. Severity: medium.
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.
