An expert car mechanic has urged motorists to think twice before filling up at supermarket forecourts.
Reaz, who has 17 years' experience in the trade and runs his own garage, said drivers should steer clear of fuels sold by Tesco, Asda, Morrisons and Sainsbury's.
He told GSF Car Parts that supermarket fuel often lacks the "necessary detergents" to keep engines clean.
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The mechanic advised alternating between premium and standard petrol or diesel, calling it a "simple practice that can extend the life of your vehicle's engine."
Specialists at Allied Autocare have raised similar concerns, warning that budget fuel may be lower quality than branded alternatives.
They said: "Retailers like BP, Shell and Esso sometimes put additives into their fuel to help boost the fuel efficiency of your car.
"This means that fuel from supermarkets, without these additives, could be costing you more in the long run. This concoction of additives can improve fuel efficiency and help keep your car engine clean. It could be a case of getting what you pay for."
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Tesco defended its Momentum 99 product, saying: "Our Momentum 99 petrol contains a special blend of additives to help keep a car's fuel system clean and working at its best.
"Additionally, the higher octane level (99 compared to 95 for regular unleaded petrol) gives improved overall engine performance for cars that are able to take advantage of this (generally, sportier models)."
Asda stressed: "There is no such thing as 'supermarket fuel' – our fuel conforms to the same standards and comes from the same refineries as the branded oil major petrol stations. We also have a dedicated fleet of tankers to ensure the quality is maintained from the refinery through to the pumps."
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Morrisons highlighted value for money, saying: "We aim to be competitive with our petrol prices and they do change to ensure we give our customers great value. Prices are not available on our website but are displayed on the totems at your local petrol station."
Sainsbury's added: "We want to ensure our petrol stations remain competitive within their local area, offering customers a fair price wherever they live. We therefore adjust the price at each station using locally gathered pricing information."
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