IsItAGoodCar
Reliability Guide

Common Problems with the
1974 Datsun 240Z / 260Z

The 260Z took over from the 240Z in UK showrooms from 1974, fitted with the larger 2.6-litre L26 inline-six and continuing the S30's refined grand-touring formula. UK 240Z/260Z sales totalled just 3,636 cars and ended in August 1979 when the 280ZX arrived, so every surviving UK 260Z is scarce.

What changed for 1974

  • •Larger 2.6-litre L26 inline-six replacing the 2.4-litre L24
  • •2+2 grand-tourer layout continued from the 240Z range
  • •UK sales ended August 1979 with the arrival of the 280ZX

Common MOT watch-outs

  • !Structural rot in sills, floor pans and chassis legs common to all S30 Z-cars
  • !Worn Hitachi carburettor needles and vacuum leaks causing poor idle and emissions failures
4
Known Issues
2
Serious
2
Moderate
0
Minor

All Known Issues

Structural Corrosion (Rust)

SeriousBodywork & Rust

The S30 chassis has many hidden box sections where moisture traps and eats the metal from the inside out. Frame rails, battery trays, and floor pans are the most common failure points.

Est. Repair Cost: £5,000–£20,000+
Warning Signs:

Bubbling paint, Soft spots in floor/sills, Doors not aligning (suggesting chassis flex), MOT failure for structural rot

What to Inspect:
  • Magnet test on sills and arches
  • Hammer tap on frame rails
  • Check under the battery tray for acid/water damage
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Overheating & Head Gasket Failure

SeriousCooling System

Older L24/L26 engines can suffer from silt buildup in the radiator or blocked coolant passages in the block, leading to localized overheating and warped heads.

Est. Repair Cost: £1,000–£3,000
Warning Signs:

Temp gauge climbing in traffic, White smoke from exhaust, Mayo-like sludge under oil cap

What to Inspect:
  • Condition of coolant (should be clean)
  • Ask when the water pump/radiator was last replaced
  • Test for exhaust gases in coolant
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Carburetor & Fuel System Issues

ModerateFuel System

The Hitachi-SU carburettors require regular maintenance and adjustment. Worn needles, vacuum leaks and gummed-up passages cause flat spots, poor idle and hesitation. Parts are hard to source, with many owners converting to Webers.

Est. Repair Cost: £200–£600
Warning Signs:

Hesitation on acceleration, Stalling at idle, Rich or lean running, Strong fuel smell

What to Inspect:
  • Check for smooth throttle response through the range.
  • Look for fuel leaks around carburettors.
  • Inspect fuel lines for perishing.
  • Ask if Weber conversion has been done.
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Wiring Loom Degradation

ModerateElectrics & Electronics

After 45+ years, the original wiring loom becomes brittle. Corroded fuse connections, cracked insulation and perished earth straps cause intermittent electrical faults throughout the car.

Est. Repair Cost: £100–£500
Warning Signs:

Intermittent lighting failures, Gauge erratic behaviour, Flickering dashboard lights, Blown fuses

What to Inspect:
  • Inspect fuse box for corrosion.
  • Check all earth points for clean metal contact.
  • Test all electrical systems including lights and gauges.
  • Consider a relay upgrade for headlights.
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Buying Tips for 1974 Datsun 240Z / 260Z

  • Distinguish a 260Z by its L26 engine badge; UK examples are rarer than 240Zs
  • Prioritise a sound floorpan and chassis over cosmetics - replacement panels are scarce
19731975–1978
Check a 1974 Datsun 240Z / 260Z by Registration