What stops oil temperature being in mind — partly fool in vehicle (12)
I believe the answer is:
antimacassar
'what stops oil' is the definition.
(cloth protecting an item from macassar oil)
'temperature being in mind partly fool in vehicle' is the wordplay.
I cannot quite see how this works, but
'temperature' could be 't' (abbreviation) and 't' is found in the answer.
'fool' could be 'ass' (both can mean a stupid person) and 'ass' is found in the answer.
'vehicle' could be 'car' (car is a kind of vehicle) and 'car' is found in the remaining letters.
'mind partly' could be 'anima' (part of the mind in Jungian psychology) and 'anima' is located in the leftover letters.
No letters remain.
This may be the basis of clue (or it may be nonsense).
(Other definitions for antimacassar that I've seen before include "Chair back protector" , "It keeps hair oil off the back of a chair" , "Cloth protecting chair from grease" , "Covering to protect the back of a chair from hair oils" , "Protective cloth on upholstered seat" .)