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

I’m 95% sure ProjectFarm (YT channel) has done this exact test among many other thorough substance/brands-mechanical experiments.