gasoline tank vs gas tank

gasoline tank and gas tank both are nouns.

Word	Noun	Adjective	Verb	Adverb
gasoline tank	Yes	No	No	No
gas tank	Yes	No	No	No

As nouns, gasoline tank and gas tank are synonyms defined as:

gasoline tank and gas tank: a tank for holding gasoline to supply a vehicle

Other synonyms of gasoline tank include petrol tank.

gasoline tank (noun)	gas tank (noun)
a tank for holding gasoline to supply a vehicle	a tank for holding gasoline to supply a vehicle