why can cooking oil be used in a car

[Petunia]

No, you should not use standard cooking oil directly in a modern car. While it is technically possible to power a diesel engine with vegetable oil, doing so requires significant modifications to both the fuel and the vehicle. The core issue is viscosity. Straight vegetable oil (SVO) is much thicker than diesel fuel, especially when cold, which can lead to poor atomization, clogged filters, and severe engine damage over time.

The process isn't as simple as pouring fryer grease into your tank. To be used safely, waste cooking oil must be rigorously filtered and processed into biodiesel, a certified fuel alternative. This conversion process involves a chemical reaction called transesterification, which reduces the oil's viscosity and alters its combustion properties to be compatible with diesel engines. Even then, most vehicle manufacturers do not warrant the use of SVO or homemade biodiesel, as it can degrade seals and injectors not designed for it.

For a standard gasoline-powered car, which most Americans drive, using any type of oil is completely ineffective and will likely destroy the engine.

Factor	Standard Diesel Fuel	Straight Vegetable Oil (SVO)	Processed Biodiesel
Viscosity	Low; flows easily	Very high; thick like syrup	Modified to be similar to diesel
Engine Modifications Required	None	Yes (two-tank heating system)	Possibly minor; check manufacturer
Cold Weather Performance	Excellent	Poor; solidifies	Good with proper additives
Long-Term Engine Impact	Minimal (with maintenance)	High risk of deposits and damage	Varies by blend and quality standards
Manufacturer Warranty	Covered	Typically voided	Sometimes approved for specific blends

While the idea of a cheap, renewable fuel is appealing, the practical challenges and risks make it an unsuitable option for the average driver. If you're interested in alternative fuels, consider a vehicle approved for biodiesel blends (like B5 or B20) available at commercial fueling stations.

[LeAddyson]

Absolutely not in a regular car. My uncle tried this years ago with an old diesel truck. He had to install a separate fuel line and a heater just to thin the oil enough for the engine to run. Even then, it smelled like a fast-food joint and was a constant hassle. For any car made in the last 20 years, it's a one-way ticket to a ruined engine. Just stick with the fuel your owner's manual specifies.

[ElijahLee]

It's a common misconception. The engines that can run on oil are diesel engines, not gasoline engines. Diesel works by compression ignition, and vegetable oil has enough energy density to combust under similar conditions. However, its thickness is the problem. Without being chemically converted into biodiesel first, thick oil can clog fuel injectors and cause expensive damage. It's not a viable fuel for a modern vehicle without serious, expensive modifications.

[VanJeffrey]

It’s a clever thought, but the chemistry is all wrong for today's precision engines. New cars have fuel injectors that operate at incredibly high pressures. They're designed for the specific thinness and properties of gasoline or diesel. Dumping thick, viscous cooking oil into that system would be like trying to pump molasses through a hypodermic needle. You'd likely foul the injectors and the catalytic converter, leading to repair bills that far outweigh any perceived savings on fuel.

[McRosalie]

From an environmental standpoint, the idea has roots in the biodiesel movement, which aims to replace fossil fuels. The key step is conversion. Raw plant oil must be transformed into biodiesel through a chemical process to make it a clean-burning, viable fuel. Using unprocessed oil is inefficient and can increase harmful emissions. So, while the concept of recycling waste oil into energy is sound, the execution requires proper industrial processing, not a direct substitution at home.