If your car is dirtier than a pig that's just had the time of its life in a patch of mud then you might be paying more for petrol than you need to.
At least that's what the experts say, as they've said that a clean car is sleeker and more aerodynamic so it uses less petrol.
Graham Conway, Managing Director at Select Car Leasing told the Mirror that there had been experiments into how much cars being dirty mucked with their performance.
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That's not the only cost to having a dirty car, so as much as you might have been putting it off it might be time to pay your local car wash a visit.
If the outside of your car is dirty then you can be fined up to £1,000 depending on how much the muck covers.
You'll definitely want to make sure your number plate is visible before heading out as that could land you a hefty fine, while a dirty windscreen which obstructs your vision can also get you in trouble and fined.
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As for saving money on petrol, Conway explained what the experiments done on dirty cars had discovered.
He said: "A cleaner car is in fact more fuel efficient.
"Experiments found the vehicle was more fuel-efficient when clean, averaging two miles per gallon (mpg) more than when it was dirty.
"The average fuel mileage of the dirty car fell to around 24 mpg, while the clean car was 26 mpg.
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"If you extrapolate that over an entire year, and with a driver covering around 8,000 miles, there’s a potential saving of around £200 annually just by keeping your car clean."
Cars are made to be aerodynamic so a cleaner car will make the most of the sleek contours of the vehicle and allow the car to move while using less fuel.
On top of that dirt can weigh down your car even if it doesn't look like much more than just a muddy cover and cost you even more in fuel.
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It might not be a massive difference but if you had the choice between two otherwise identical cars where one did 24mpg and the other did 26 you'd pick the second one every time.
When it comes down to it taking a bit of time to wash the car and keep it in a good condition sounds like the better option in the long run.
As an added bonus you'll also miss out on the silent judgment from other drivers.
Joe Harker