Smooth, yes, but you don't want all that oil! (5)
I believe the answer is:
slick
This clue could be a double definition.
'smooth yes but you don't want all that' is the first definition.
'slick' can be an answer for 'smooth' (I've seen this in another clue). I'm not sure about the remainder of the definition.
'oil' is the second definition.
(thesaurus)
Can you help me to learn more?
(Other definitions for slick that I've seen before include "Meretricious" , "Smooth" , "Sleek - film of oil" , "Smart" , "polished performance" .)