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 oil needs to remain chemically stable at engine operating temperatures, which will routinely exceed 200F and have some areas even hotter than that.

Most food oils aren’t chemically stable under those conditions.

Then there are other concerns with cold viscosity (your oil can’t be frozen!) and lubrication (can’t be too watery!), but first you have to not burn up.