can you use animal fat in your car

[JaydenLee]

No, you should not use animal fat as fuel or lubricant in a modern car. While chemically possible to create a biodiesel-like substance from animal fat through a process called transesterification, using raw or improperly processed fat in your vehicle will cause severe and costly damage to the engine and fuel system. Modern diesel and gasoline engines are precision-engineered for specific fuel properties, and animal fat does not meet these requirements.

The primary issue is viscosity. Animal fat is far too thick at room temperature and will solidify, clogging fuel filters, injectors, and fuel lines. This can lead to a complete engine failure. Furthermore, its combustion properties are unsuitable, potentially causing incomplete burning, excessive carbon deposits on injectors and pistons, and damage to emission control systems like the Diesel Particulate Filter (DPF). While "grease cars"—older, mechanically simple diesel vehicles with modified dual-tank systems—can run on waste vegetable oil, they still require extensive filtering and heating. Animal fat presents even greater challenges due to its higher saturation, which promotes solidification.

The following table compares key properties of standard diesel fuel with animal fat, illustrating why it's a poor substitute:

Property	Standard Diesel Fuel	Animal Fat (Tallow)	Impact of Using Animal Fat
Viscosity (@ 40°C)	2.0-4.5 mm²/s	~45 mm²/s (heated)	Clogs filters and injectors; poor atomization
Cloud Point	Varies by season, e.g., -10°C to -15°C	~45°C (113°F)	Solidifies at high temperatures, blocking fuel flow
Cetane Number	40-55	~40 (after processing)	Poor ignition quality, leading to rough operation
Energy Content	~130,000 BTU/gallon	~120,000 BTU/gallon (processed)	Reduced fuel economy and power
Oxidative Stability	High	Very Low	Rancidity and acid formation corrode fuel system components

Stick to manufacturer-recommended fuels and lubricants. The risks of experimenting with animal fat far outweigh any potential cost savings, potentially leading to repair bills that exceed the value of the vehicle itself.

[OCorbin]

Trust me, as someone who’s tinkered with old engines, it's a terrible idea. It might seem like a clever hack, but you’re asking for a world of trouble. That fat will turn into a waxy, greasy clog in your fuel system before you even get down the block. You’ll be dealing with tow trucks and mechanic bills instead of saving money. Just use the proper fuel. It’s not worth the risk.

[OQuinn]

From a purely chemical perspective, the hydrocarbons in animal fat can be burned. However, the practical application is where it fails. Modern fuel injection systems rely on precise atomization of a thin liquid. Animal fat's molecular structure is too large and complex, leading to incomplete combustion. This creates harmful deposits that degrade engine performance and increase emissions. The chemistry simply isn't compatible with today's engineering standards.

[MacAvery]

I think the idea comes from old stories or survival scenarios, like people using whale oil in lamps. But a car isn't a simple lamp. It's a complex computer on wheels. The fuel pump, injectors, and sensors are designed for a very specific liquid. Pouring in rendered fat would be like trying to run a smartphone on potato battery power—the fundamental technology is mismatched. It might have worked in a primitive engine, but not in anything built in the last 40 years.

[EvaLee]

The biggest immediate danger is to your fuel filter and injectors. They are designed for clean, refined fuel. Animal fat contains impurities and solidifies easily, causing blockages that starve the engine of fuel. This can happen quickly, leaving you stranded. Long-term, the fat can coke onto piston rings and valves, leading to loss of compression and a need for a prohibitively expensive engine overhaul. The potential damage is severe and irreversible.