Why can’t we use something like vegetable oil as a replacement for engine oil?

Question

Cooking oils also go to high temperatures. Do they expire before a synthetic would?

Edit:

Wasn’t wondering to make a substitute. It’s not an environmental or political question. Just wondering the *why* (:

Thanks so much to everyone who answered!

In: Chemistry

Answer 1

Engine oils are designed to provide lubrication for the engine. Oils are used because of their viscosity. However, temperature effects cause changes in the viscosity of the oil. Low temp = more viscous and high temp = less viscous. Engines are designed to operate with a certain range of viscosity. If the oil is too viscous, it won’t circulate properly, and will reduce lubrication, and gum up the small passages it flow through. If it’s not viscous enough, it won’t provide enough lubrication, and will cause excess engine wear.

So when you see an oil rating like 10w30, this tells you the viscosity rating of the oil at different temperatures. The number is a standard set by ASE, where a lower number is more viscous and a higher number is less viscous. In our example, 10w means the oil will be an ASE 10 viscosity at winter temperatures (32F), hence the W for “winter”. The 30 indicates a viscosity of ASE 30 at high temperature (212F). Different engines are designed for different oil ratings depending on how tight the tolerances of the engine are, how much heat the engine creates, etc.

The problem with plant based oils is that they are way too temperature sensitive, and generally not viscous enough. They are also extremely expensive relative to hydrocarbon based lubricants, and not practical to scale. It just to expensive and hard to spend a year growing a plant to extract 2% of the weight of the plant. So, even if it did work, we don’t have enough farms to make it happen and feed ourselves.