A car engine stalls, refuses to start, and then a whiff of frying oil rises from the tank. For many drivers, that’s the nightmare scenario. In Besançon, in the Doubs region of eastern France, a mechanic didn’t even need to open the hood fully to pinpoint the fault: “You can smell a hint of frying oil,” explains Charly Petitjean, owner of Vulco garage, speaking to TF1. His customer had simply mixed frying oil with diesel to save money at the pump.
The bill, however, is nothing like a smart bargain. “For about twenty euros saved at the pump, you end up, as with this car, replacing two injectors, which comes out to roughly 800 euros,” says Charly Petitjean. The mechanic has already seen a second car that same week for the same reason. And he’s not alone: amid soaring fuel costs and viral videos on social media, some people literally turn their frying-oil as car fuel, or fill their tanks with heating oil, red diesel, or homemade ethanol blends, with real risks attached.
Frying oil, red diesel, and GNR: what people replace regular fuel with
Facing a diesel or gasoline fill-up that easily tops €100, the lure of do-it-yourself hacks grows. In the TF1 report, the motorist who broke his injectors tried replacing part of the diesel with frying oil, sometimes rapeseed oil, to save a few tens of euros. This kind of blend remains completely illegal for a private individual. The same goes for heating oil or off-road diesel, recognizable by their red color, which are taxed differently and often cost 40 to 60 cents less per liter than road diesel. These products are reserved for heating or for agricultural and construction equipment. A private person who puts them in a car faces hundreds of euros in fines at a checkpoint, and the Customs Code provides, in cases of clearly established fraud, penalties that can go as far as years in prison and heavy fines calculated on the mileage driven.
And then there are the “eyed” blends with superethanol-E85. At a gas station, a young driver candidly describes his habits when the bank account is tight: “When the bank account isn’t flush, we mix; we add a bit of unleaded 95 with ethanol as well. We’re still afraid of messing up, but we do what we can,” says the young motorist interviewed by TF1. On paper, superethanol-E85 sounds appealing: a 50-liter fill currently costs about €45.50, compared with €105.50 for 50 liters of unleaded, an $60 gap. But this fuel is only allowed in vehicles designed for it, either from the factory or converted with an approved kit; in other cases, these rogue blends can seriously damage the engine.
From mechanical damage to insurance: the true cost of these “savings”
For professionals, these hacks become obvious immediately. In Besançon, the frying-oil mixed with diesel was enough to seize two injectors, ultimately preventing the engine from starting at all. On modern direct-injection diesels, highly sensitive to fuel quality and viscosity, this kind of mixture triggers accelerated deposits, residue in injectors and the pump, and sometimes outright engine failure. Where some older diesels could tolerate a little oil, today’s units operate at very high pressures, and the slightest impurity or viscosity drift can be the difference between a rough idle and a complete stall. The immediate saving of about $22 at the pump turns into hundreds of dollars in parts and labor, as the customer of Charly Petitjean experienced.
Counterfeit fuels also raise legal and safety concerns. If heating oil or off-road diesel ends up in a tank, a fuel check can lead to immobilization or even confiscation of the vehicle, with hefty fines and, in the most serious cases, up to three years in prison. The risks don’t stop there: using a fuel not supported by the manufacturer—whether raw frying oil or an unapproved E85 blend—can void the mechanical warranty. In a serious accident, an insurer-appointed expert can analyze the fuel, and if it proves noncompliant, the payout can be denied. On the flip side, there is a regulated pathway where used cooking oil is collected, filtered, and converted into fuel for captive fleets, delivering up to about a 90% reduction in greenhouse gas emissions versus fossil diesel. But even then, the vehicles must be properly adapted, the tax handling must be reported, and everything monitored. For the general public, the only genuinely low-cost option with real oversight remains superethanol-E85, provided you have a compatible car or a certified kit, which typically costs between $500 and $1,000, as one industry professional notes: “Bioethanol is a drier fuel,” says Yves Adrien, manager of Neves Auto in Champigny-sur-Marne, speaking to TF1, explaining that injection timing must be adjusted for the engine to run smoothly. More than 400,000 vehicles have already been adapted in France, a figure that underscores why these legal solutions are attractive when every trip to the pump becomes a budgeting headache, far from improvised blends of frying oil or red diesel.
