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How Long Can You Leave A Car Without Starting It?

How Long Can You Leave A Car Without Starting It?

Whilst using a car regularly causes wear and tear to the engine, suspension and other components, leaving a car unused without starting it can cause problems in itself. If you stop driving your car for an extended period of time, you should be aware of the best practices we’ll detail below. 

What happens to your car if you don't use it? 

Leaving a car to sit can cause damage and require the replacement of certain parts, such as: 

Tyres 

Rubber perishes with time and exposure to sunlight, even when not used. This is accelerated by the tyres having low pressure from a slow puncture or not being inflated regularly.  

If the tyres lose all their pressure, the sidewalls can crack and the tyres develop a ‘flat spot’ in a matter of weeks, rendering the tyre too damaged to be used.  

Hoses 

Hoses are used in various systems on modern cars, including the cooling, air conditioning, steering and brakes. All rubber hoses deteriorate faster when not used, meaning after a few months leaks can develop in various places. 

Suspension Joints 

Along with hoses and tyres, many suspension and engine mount bushes are made of rubber, these too deteriorate faster when sat in the same position for a long time.  

Battery drain 

Various systems like the alarm, immobiliser and even some ECU functions still operate even when the car is not in use. This is known as a parasitic draw, and it is impossible to avoid completely. Without frequent use of the car, this can cause the battery to become depleted. 

How long can you leave a car without starting it? 

If you’re not regularly driving your car, it's advisable to start the engine at least once a week, allowing it to run for at least half an hour. It would be ideal to drive the car for a short journey too, this would help keep the battery charged.  

How to keep the battery healthy in an unused car 

There are a few things you can do to stop the battery from being damaged from lack of use, with the correct steps a battery can be kept unused for years. 

1. Remove the battery and store it 

Current draw from the car's electrical system, and changes in temperature both affect the battery's health. Removing the battery from the car and keeping it inside, in a reasonably stable environment keeps the battery from deteriorating. 

Make sure to charge the battery fully before removing it, either by taking the car on a long drive, or charging it using a battery charger.  

2. Trickle charging 

Most battery chargers have a trickle charge function, this keeps the battery topped up with a small amount of current constantly. This prevents the battery fluids from crystallising and prevents the battery's capacity from being diminished.  

If you don't have a garage or the ability to get power to the vehicle where it’s parked, there are solar-powered trickle chargers that can maintain a battery purely from solar power. 

What happens to a car battery if unused?

If you allow your car battery to become fully discharged for too long or too many times, it will no longer have the same capacity as before and may need replacing soon. 

When a car battery discharges, the liquids solidify into crystals inside the battery. When the battery is charged up again, the crystals are dissolved and the liquid enables the voltage potential to be restored, restoring the power in the cells. 

The problem comes when the battery is fully discharged too many times or for a long time, the crystals build up excessively and cannot be effectively liquidated, which severely limits the capacity of the battery.  

What happens to a car if unused for 2 weeks?

Modern cars should be okay left unused for a fortnight, it is not enough time for the tyres and other rubber components to perish, as well as suspension joints and wiper blades.  

Make sure you top up the tyre pressures and the battery charge - even just by taking the car on a long drive - before parking. Especially check no interior lights or other electrical components are left on. 

What happens to a car if unused for a month?

30 days of inactivity could cause some issues, especially on older cars. The most likely issue will be a dead battery. This can be mitigated by either disconnecting and removing the battery, or using a trickle charger as described previously.  

What happens to a car if unused for 6 months? 

6 months is quite a long time to leave a car unused. If left as is, the battery will almost certainly be flat, and probably not able to take a full recharge. It is also likely that one or more of the tyres will have deflated.  

If a tyre has deflated, it will most likely need to be replaced, as the sidewall will have been stressed excessively at one point, and caused cracking. 

Any fuel left in the car’s tank will likely have deteriorated to the point where the car will not run properly using it. 

What happens to a car if unused for a year or more? 

After a year, as well as the other issues listed above, it is likely that some rubber perishing on hoses, bushed and tyres will have occurred. This may present itself in small leaks on coolant, vacuum or air conditioning hoses, as well as creaking/knocking suspension.  

To fix a car that has been left for over a year, it would probably need new tyres, some new suspension bushes, a new battery and a substantial inspection from a mechanic.  

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