Drivers issued 30-day warning over fuel in petrol and diesel cars

Petrol and diesel fuel can "degrade" within just one month, according to leading motoring experts. Specialists at BigWantsYourCar stressed that fuel sitting in a tank for just 30 days can start to go stale in a major blow for motorists.

Petrol or diesel sitting in tanks for too long can cause some issues, with experts warning that "reduced performance" and "rough starts" are likely. Fuel sitting in a tank for too long can even cause "engine knocking" in a far more serious issue that could leave motorists panicked. Heat can speed up deterioration, meaning those leaving their cars parked up for an early September holiday could be caught out.

A spokesperson for BigWantsYourCar said: "Petrol starts to degrade in as little as 30 days, and high temperatures can accelerate the process.

"Fuel that's been sitting in the tank for too long can lead to rough starts, reduced performance, or even engine knocking. Diesel lasts a little longer but isn’t immune, especially if condensation builds up in the tank and causes microbial growth."

Experts at FuelGenie claim the cut-off is a bit later, with fuel likely to start degrading at around the six month mark. The RAC explained fuel may only last around three months at 30 degrees and could degrade faster the more it is exposed to heat.

However, FuelGenie claims motorists returning to a car after some time away may notice the engine won't start as effectively. This is one of the major warning signs that fuel is going off and may require the tank to be drained.

However, they stress that driving a vehicle with degraded fuel shouldn’t cause permanent damage to the engine.

The experts explained: "As well as knowing how long fuel has been stored in a container or kept in a tank, you can tell if petrol or diesel has expired by its look and smell.

"If the fuel looks dark or muddy in appearance or it has a sour, spoiled smell that isn’t typical of petrol or diesel, then it’s likely to have gone off.

"If you try to start the vehicle and the ignition doesn’t kick in immediately, this is also an indication that the fuel has expired."