This question might be a bit weird, but I just asked myself why a wooden spoon creates bubbles when put in oil at about 170°C. My idea is, that the water in the spoon reacts with the Oil, but why does this just starts to happen when the Oil reaches approx 170°C? Why does this not happen at 100 or 120°C ?
Wooden spoons are porous, and have oil, water, and air embedded in their surfaces after being used for a while.
Putting a spoon like this into hot oil will boil the water in the surface, and expand any air there, thus creating bubbles of water vapor mixed with air.
If you then allow the oil and the spoon to cool off together, the remaining air in the (hot) spoon will contract and pull oil into the deep pores of the wood as it does. This will form a thick layer of oil-saturated wood on the spoon surface, and suppress bubble formation the next time you stick it into a container of hot oil.
I doubt whether this has to do with the content of the spoon, as old and new spoons behave in the same way. I suspect the reason is that oil is a mixture of different oils, and that oils with smaller molecules have a lower boiling temperature. The oil may contain a small proportion with a boiling temp of about 170°C. The spoon has a rough surface on which bubbles are more likely to form. You could test this by seeing whether any other objects with a similar rough surface have the same effect.