What Does a Seized Engine Mean?
An engine seizes when internal components bind together or lock up, preventing the crankshaft from rotating. The starter motor may groan, strain, and then click off, or the key may just produce a heavy clunk with no movement whatsoever. Unlike a dead battery (where the starter spins freely but weakly), a seized engine presents as a mechanical inability to rotate.
This is one of the most serious and potentially most expensive automotive problems a NZ driver can face.
Common Causes of Engine Seizure
Oil starvation is the most common cause. Without adequate lubrication, metal-to-metal contact generates heat rapidly. Piston rings, connecting rod bearings, and main bearings can weld themselves to cylinder walls and journals within minutes. Causes include:
- Running the engine with critically low or no oil (ignored oil pressure warning light)
- Oil system failure (oil pump failure, blocked oil pickup)
- Extended oil change intervals on a high-mileage engine
Hydraulic lock (hydrolock) — water enters the cylinders (from a flood, failed head gasket, or leaking inlet). Water doesn't compress. When the piston tries to compress a cylinder of water, it bends or breaks a connecting rod or cracks the block. You can't start a hydrolocked engine safely.
Rust seizure — a vehicle left sitting for a long period (months to years) can develop rust on the cylinder walls that bonds the piston rings in place. The engine turns with extreme difficulty or not at all.
Overheating — severe overheating can warp pistons and cylinder heads, causing physical binding.
Broken internal component — a snapped timing chain, broken connecting rod, or dropped valve can lock up the engine immediately.
How to Confirm Seizure vs. Starter/Battery
Put the car in the highest gear (manual) and try to push it forward. If the car won't roll and there's a grinding or clunking resistance from the drivetrain area, the engine is seized. If it rolls freely, the engine itself is likely fine and the starter circuit is the issue.
Alternatively, a mechanic can attempt to turn the engine by hand using a breaker bar on the crankshaft pulley bolt. A seized engine won't turn at all; a healthy engine turns with moderate effort.
What It Means for Repair
A seized engine usually means:
- Rebuild: Strip the engine, replace damaged components (bearings, rings, pistons, possibly cylinder head), reassemble. Cost: $3,000–$8,000+ NZD depending on extent of damage and vehicle.
- Engine replacement: Fit a used or remanufactured engine. Used engines from Japanese imports are often available. Cost: $2,500–$6,000 NZD fitted.
- Write-off: For an older, lower-value vehicle, the repair cost may exceed the car's worth. Get a quote from two or three mechanics before deciding.
WoF Implications
A car with a seized engine can't be driven. Beyond the WoF, this is a total repair situation before the vehicle is road-legal again.