1972 Datsun 240Z Problems: 6 Known Issues

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.

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.

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.

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.

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.

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.