Why Is My Car Using More Fuel Than It Used To? (And What You Can Do About It)

If you've noticed you're filling up more often than you used to, you're not imagining it. Fuel economy naturally degrades over time — but the good news is that most of the causes are easy to identify and cheap to fix. Here's what's likely going on under the bonnet.

1. Dirty or Worn Fuel Injectors

Fuel injectors that are clogged or worn don't atomise fuel efficiently, meaning your engine burns more fuel to produce the same power. This is one of the most common causes of increased fuel consumption in older vehicles.

Fix: A quality fuel injector cleaner added to your tank every 3,000-5,000 miles keeps injectors clean and firing correctly. Products like Wynn's Injector Cleaner or similar fuel system treatments dissolve deposits without needing a garage visit.

2. Old or Incorrect Engine Oil

Engine oil that's past its service life becomes thicker and creates more internal friction. Your engine has to work harder — and burn more fuel — to overcome that resistance.

Fix: Stick to your manufacturer's recommended oil change intervals and always use the correct viscosity grade. Switching to a fully synthetic oil can also improve fuel economy by 1-3%.

3. A Clogged Air Filter

Your engine needs a precise mixture of air and fuel to combust efficiently. A blocked air filter restricts airflow, forcing the engine to compensate by using more fuel.

Fix: Air filters should be replaced every 12,000-15,000 miles or annually. It's one of the cheapest and easiest DIY maintenance jobs you can do.

4. Underinflated Tyres

Soft tyres increase rolling resistance — your engine has to work harder to move the car. Even tyres that are 5-10 PSI below the recommended pressure can increase fuel consumption by 2-3%.

Fix: Check tyre pressure monthly and before long journeys. The correct pressure is in your vehicle handbook or on the sticker inside the driver's door frame.

5. A Failing Oxygen Sensor

The oxygen sensor monitors exhaust gases and tells your engine's ECU how to adjust the fuel mixture. A faulty sensor can cause the engine to run rich — burning far more fuel than necessary.

Fix: If your engine warning light is on alongside poor fuel economy, get the fault codes read. A failing O2 sensor is a common culprit and relatively inexpensive to replace.

6. Carbon Buildup in the Engine

Over time, carbon deposits build up on intake valves, pistons, and combustion chambers. This reduces combustion efficiency and increases fuel consumption — particularly in direct injection engines.

Fix: A periodic engine flush or carbon cleaning treatment can remove these deposits and restore efficiency. Products like Forte or Wynn's engine treatments are designed specifically for this.

7. Short Journeys and Cold Starts

Engines are least efficient when cold. If most of your driving is short trips under 5 miles, your engine rarely reaches optimal operating temperature — meaning it runs on a richer fuel mixture for a higher proportion of your driving.

Fix: Combining short errands into one trip helps. If short journeys are unavoidable, a fuel system cleaner used regularly helps offset the effects of frequent cold starts.

8. Driving Style and Habits

Aggressive acceleration, late braking, and high motorway speeds all significantly increase fuel consumption. Air conditioning also adds load to the engine, particularly at low speeds.

Fix: Smooth, anticipatory driving — accelerating gently and reading the road ahead — can improve fuel economy by 10-15% on its own.

The Bottom Line

Increased fuel consumption is rarely caused by one single thing — it's usually a combination of small factors adding up. The good news is that regular maintenance, the right fuel additives, and quality lubricants can make a measurable difference to your running costs.

Browse our range of fuel additives and engine treatments to find the right products for your vehicle.