Is It Cheaper To Have A Full Petrol Tank Or Keep Topping It Up?

With fuel prices fluctuating across Spain in 2025, many drivers are seeking ways to save money at the pump. One common question arises: is it more economical to keep your petrol tank full or to top it up regularly? Let's delve into the details to find out.

Understanding fuel evaporation and weight

Modern vehicles are equipped with sealed fuel systems, which significantly reduce fuel evaporation. So the difference in evaporation between a full tank and a half tank is negligible. Some drivers argue that less petrol means less evaporation, while others say keeping the tank full avoids faster fuel degradation. In reality, the fuel system design makes this debate largely irrelevant for most modern vehicles.

On the other side, a full tank adds weight to your vehicle — around 30 to 40 kg depending on fuel type and tank size. Added weight can slightly reduce fuel efficiency, particularly in stop-start city driving. But the difference is marginal — typically around 1% or less in overall consumption.

Refueling frequency and practical cost

Drivers who top up a little at a time may find themselves visiting the petrol station more frequently, which not only consumes more of your time but could lead to extra fuel usage if your route requires a detour. Frequent refueling also increases the temptation to spend on snacks or impulse buys while inside the petrol station.

If your weekly schedule is tight, the real saving might come from efficiency of time rather than cost per litre.

Mechanical benefits of keeping the tank fuller

Driving with a nearly empty tank frequently can harm your fuel pump. Petrol acts as a coolant for the pump, and when levels are low, it may overheat — leading to wear or failure. Additionally, sediment at the bottom of older fuel tanks can clog filters if it’s stirred up by running too low too often.

Keeping at least a quarter tank is often recommended to maintain pump health and avoid unnecessary wear.

Conclusion on the main debate

In terms of fuel cost, there’s no major benefit to filling the tank fully versus topping up in small amounts. The impact on weight and evaporation is minimal. However, there are practical reasons to keep your tank above a quarter full — including mechanical reliability, fewer station trips, and more peace of mind.

Practical ways to save fuel in Spain (2025)

Use fuel comparison apps – Try apps like GasAll, Waze, or Google Maps to find the cheapest nearby stations. Price differences can be up to 20 cents per litre in some areas.

Check your tyre pressure monthly – Underinflated tyres increase drag and reduce mileage. Tyre Pressure Monitoring Systems (TPMS) help, but a manual check ensures accuracy.

Lighten your load – Remove heavy or unnecessary items from your boot. Leave roof racks and boxes off unless you're using them. Less weight = more mileage.

Drive with care – Accelerate gently, avoid harsh braking, and shift gears early in manual cars. On motorways, cruise control can help maintain consistent speeds and improve fuel economy.

Minimise air-con usage – Air conditioning increases fuel use, especially at lower speeds. Use natural ventilation when you can.

Avoid idling for long periods – If you’re stationary for over a minute, switch off the engine. Restarting uses less fuel than you might think.

Combine errands into single trips – A warm engine is more efficient than repeated cold starts. Plan ahead and group outings together.

Fuel up mid-week – Petrol prices often rise before weekends and holidays. Refueling on Tuesday or Wednesday morning can sometimes save you a few cents per litre.

Long-term savings tip: Track your consumption

Use a fuel log app or a simple notebook to track your consumption, average cost per fill-up, and driving habits. Many expats find that small adjustments lead to noticeable monthly savings.

Does this advice apply to hybrids and electrics?

The full tank vs topping-up debate only applies to petrol and diesel vehicles. If you're driving a hybrid, fuel economy tips still help — particularly smooth driving, tyre checks, and reduced load. For full EVs, the equivalent would be charging habits and route planning for energy efficiency.

Real-world example

Let’s say your tank holds 50 litres and fuel costs €1.60/litre. Whether you fill it once a week or top it up with 10 litres five times, the total cost is the same: €80. However, you’ve spent more time driving to the pump, and possibly detoured 10 km roundtrip each visit. That’s extra wear, extra fuel, and less convenience.

The final word

There’s no need to overthink whether you're better off topping up or filling up — the impact is negligible. But keeping your tank above a quarter full, maintaining your car, and driving smartly? That’s where the real savings lie.

Sources

20minutos.es
Wales Online
The Sun UK
Mechanics Stack Exchange
VerifyThis.com