Amount of water I put in a car (5)
I believe the answer is:
fiord
'amount of water' is the definition.
'fiord' can be an answer for 'water' (fiord is a kind of water). I'm not certain of the 'amount of' bit.
'i put in a car' is the wordplay.
'put in' is an insertion indicator.
'a car' becomes 'ford' (Ford is a make of car).
'i' placed inside 'ford' is 'FIORD'.
Can you help me to learn more?
(Other definitions for fiord that I've seen before include "Deep sea inlet as in Norway" , "Long narrow sea inlet between high cliffs" , "Long, steep inlet from the sea" .)