When it comes to storing your car for an extended period, whether due to travel, seasonal storage, or an impending break from driving, a common question arises: should you leave petrol in the tank?
The decision may seem trivial, but it can have significant consequences for both the car’s condition and your wallet. Understanding the pros and cons of leaving petrol in your car can save you from costly repairs, and in some cases, prevent potential hazards.
The Impact of Petrol on Your Car When Left in Storage
The general advice for long-term car storage often revolves around keeping your car in good condition. While leaving petrol in the tank may seem like the easiest option, it can lead to fuel degradation and damage to your vehicle’s components.
Fuel Degradation and the Risk of Old Petrol
Petrol can degrade over time. In the UK, where cars may be stored for months, the petrol in the tank can lose its combustibility, leading to poor engine performance. Petrol is composed of hydrocarbons that, over time, begin to evaporate, especially when exposed to heat. This evaporation process can lead to the formation of a varnish-like substance that can clog the fuel system.
In fact, it is reported that after around three to six months of storage, the petrol in a car’s tank can start to degrade, leading to operational issues when you attempt to start the engine again. The risk is that old petrol will fail to combust properly, causing poor ignition and engine knocking. This may require a costly fuel system cleaning or even a replacement of parts such as fuel injectors and fuel pumps.
The Effect of Long-Term Storage on Fuel Lines and Tank
Fuel left in your car’s tank can also create moisture inside the tank, particularly if the tank is only partially full. This moisture can mix with the petrol, leading to rust in the tank or the fuel lines. Over time, corrosion can occur, damaging the vehicle’s fuel system. Rust can lead to blockages or leaks that may be expensive to repair, especially if they go unnoticed for some time.
Petrol Additives and Stabilisers
Some vehicle owners opt for fuel stabilisers to prolong the life of petrol during storage. These additives can significantly reduce the risk of petrol degradation. According to experts in the automotive industry, stabilisers prevent oxidation and help maintain the petrol’s volatility for up to 12 months.
If you plan to store your car for a long period, such as over the winter months, it’s advisable to add a fuel stabilizer to the petrol before storage. Doing so can also protect the fuel system from corrosion caused by moisture.
What Happens If You Don’t Leave Petrol in the Tank?
On the flip side, some car owners prefer to drain the petrol completely from their vehicles before storage. This prevents the degradation of fuel and eliminates the risk of clogging or rusting. However, draining the fuel tank entirely isn’t always a practical solution. The process can be messy and requires you to dispose of the petrol safely.
Furthermore, leaving a fuel tank entirely empty can lead to problems, as fuel tanks are designed to have petrol inside them. A completely dry tank could result in seals drying out or cracking, leading to potential leaks.
The Case for Leaving the Tank Full
Keeping your tank full can actually be beneficial for some cars when storing them. A full tank can prevent condensation from forming in the tank, as there’s less room for moisture to accumulate. The less air there is in the tank, the less likely condensation will form, which can lead to rust and corrosion. In cold climates, a full tank also reduces the chances of water vapour in the tank freezing, which could block fuel lines and lead to starting issues.
Alternative Fuel Sources: The Rise of Electric Vehicles
With the rise of electric vehicles (EVs) in the UK, many car owners are now opting for alternatives to petrol altogether. In 2025, EV sales have seen a steady increase, with over 20% of new cars sold being fully electric.
If you’re considering switching to an electric vehicle or already own one, this shift eliminates concerns about storing petrol altogether. As electric vehicle technology continues to improve, this may become the most viable option for those looking for a hassle-free storage solution.
The Bottom Line
The decision to leave petrol in your car during storage ultimately depends on your storage timeframe, the condition of your vehicle, and your personal preferences. While leaving petrol in your car can result in fuel degradation, moisture accumulation, and rust in the long term, taking proper precautions such as using stabilisers and keeping your tank full can mitigate some of these risks.
If you’re storing your vehicle for a short period, leaving some fuel in the tank is usually safe, but for long-term storage, it might be best to consider draining the tank or using fuel stabilisers.
Whatever your choice, remember that the aim is to preserve the health of your vehicle and avoid unnecessary repairs down the line. By taking a few simple steps, you can ensure that your car is ready to hit the road again, no matter how long it has been in storage.
You might like this guide: How Often Should You Drive A Car In Storage?
