What's that Oil for again? ==

It says the main reason for using oil in old large capacitors and transformers is because of the heat generated. Funny, I thought it was used mainly as an insulating medium and dielectric. 

OK, its for cooling as well! 

But not mainly for cooling in capacitors as they shouldnt get very hot (unless thers a lot of ripple current and a high ESR). So I intend to correct this statement. 

Ive posted a dispute tag in this area, because I dont believe in general that oil is used for capacitor cooling.
Quote from manufacturer literature:

'#  Why are GAEP high voltage capacitors oil-filled?
 
Highly insulating oil is used to suppress partial discharges (corona), increase the dielectric strength, and increase the effective permittivity (dielectric constant) of the capacitor dielectric. Oil-filled film capacitors have high energy density in comparison with other types of capacitors used at high voltage, such as ceramic capacitors. Different types of oils are used with different types of capacitor dielectric and electrode designs.
' 
   
 

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