My brother is having a go at me because I apparently destroyed his Tefal fryer because I left the oil sitting. He said that "the oils been sitting too long, it's messed up the wiring underneath, and it doesn't work".
Can the oil stop the wiring from working?? I believe it can't as oil cant seep through metal, can it?
If oil is even in contact with the wires the unit is defective or has been modified, making it impossible for the oil to be the cause of electrical failure of a correctly working, unmodified unit. In addition, most oils are mostly non-reactive, that is why they are used for frying applications and can be used repeatedly. Some exotic oils may be a bit more reactive, but are not used for deep frying. The fryer units are made with the expectation they will have oil in them most of the time. Letting a unit sit too long may result in spoiled or contaminated oil, but not issues with the unit. I would respectfully suggest that your bother is mistaken and attempting to cast blame where it does not belong. I say respectfully as the actual words that come to my mind are more harsh.
This is very, mightily, unlikely (unless you have been deep-frying sulfuric acid or aqua regia :). I normally filtre and then store oil in my deep fryer; so far without problem.
If the oil vessel were leaking, I would expect it to have completely drained and sitting on the bottom of your (his) cupboard as the bottom of deep-dryers is vented. As well, oil has very low conductivity; somewhere between ionized water and damp wood (Electrical properties of vegetable oils between 20 Hz and 2 MHz), so is unlikely to short the wiring (although any contaminants may have done so).
I suspect either that the appliance just failed or somehow water got into it (did he wash it in the dishwasher?)
Cold oil is far more viscous than oil at frying temperature - remember why you usually filter oil for reuse as hot as you can get away with! Unless any seals are built in a way that they take advantage of thermal expansion (unlikely!) to seal tighter at operating temperature, they would fail during operation and not at rest with cold oil.
As mentioned already, oil is indeed a very good electrical insulator - actually, high voltage equipment is routinely filled with oil (not edible oil though) for that reason.
Still, any appliance design that could fail by letting oil into any wiring where it is not supposed to be would be defective safety-wise: While immersion in oil is a good idea for aome electrical circuitry as mentioned, having oil residue and air around wiring that could get hot is a potential fire hazard.
Oil could eventually penetrate plastic (very very slowly), but never metal, glass or non-porous ceramic...
