Let’s try to answer the question we initially posed. The answer could be “not very well.” The initial performance of the mayonnaise nearly equals the performance of good “real” thermal compounds, and lasts for about 24 hours.
After that, the cooling performance degrades. But the temperature difference stabilizes at about six degrees Celsius hotter than the initial temperature, which is not a complete disaster, but obviously places mayonnaise below the performance of commercial thermal pastes.
So, does mayonnaise last as a good thermal compound? No, it doesn’t. But does it stop working as a thermal compound? Absolutely not. After a couple of days, it works as a pretty poor thermal compound, which is better than no thermal compound at all.
Also, after 12 days the metallic cap of the CPU and the base of the CPU cooler were pretty oxidized. Even though we could remove this oxidation with a sponge, we don’t know what would happen after a longer period of time.