Why Sitting Causes Starting Problems
Vehicles are designed to be used regularly. When a car sits unused for weeks or months — common after holidays, lockdowns, medical events, or when a family member moves away — several things degrade simultaneously.
What Goes Wrong
Flat battery: A car's battery slowly self-discharges when not in use, and parasitic draw from the alarm, ECU, and keyless entry accelerates this. After 4–6 weeks, many batteries will be too flat to start the car. After 2–3 months, the battery may be damaged beyond recovery.
Fuel degradation: Petrol begins to oxidise and degrade after about 30 days, forming varnish deposits that can clog fuel injectors and the fuel filter. Ethanol-blend fuels (which are common in NZ) absorb moisture and degrade faster.
Tyre flat spots: Tyres develop flat spots where they rest on the ground, causing a thumping sensation for the first few kilometres after a long sit.
Brake corrosion: Brake discs (rotors) develop a thin rust layer within days of being unused. Usually this clears itself with a few brake applications, but on long-term storage vehicles, pads can bond lightly to the disc.
Seized brake callipers: If the handbrake was left on, rear brake pads can seize to the drum or disc after weeks of sitting.
Rodent damage: Mice and rats are attracted to parked vehicles in NZ — especially in rural and semi-rural areas. They nest in air filters and chew wiring harnesses.
How to Start a Car That's Been Sitting
- Charge or jump-start the battery. Use a trickle charger (smart charger) for several hours if possible rather than immediately jump-starting — this is kinder to the battery.
- Check for obvious issues. Open the bonnet, look for signs of rodent activity (droppings, chewed wires, nesting material), and check the oil, coolant, and brake fluid levels.
- Check the tyres. Inflate them to the correct pressure before moving the car.
- Start the car and run it. Once running, drive it for at least 20–30 minutes to recharge the battery and circulate fresh oil through the engine.
- Brake gently several times to clear any rust from the discs.
If It Won't Start
- Flat battery: jump-start or charge
- Fuel too old: drain and refuel if the car has sat more than 3–4 months
- Fuel injectors gummed: may require professional injector cleaning
- Check for fault codes before assuming a major fault
When to Service It Before Driving Regularly
After a long sit, consider:
- Oil and filter change (oil oxidises over time even without use)
- Fresh fuel if the old fuel has sat more than 3 months
- Checking the battery's health (replace if weak)
- Brake inspection for corrosion or seized components
Most mechanics can do a "recommissioning check" for $80–$150 NZD, covering the above and giving you peace of mind before WoF.