Difference between 消防车 and 救火车
This is an issue about 书面语(words that are used for writing articles) and 口语 (words that are usually used in oral Chinese)

The two words have the same meaning. However, 消防车 is more formal, it's used in most of the written materials. 救火车, on the other hand, is usually used in spoken Chinese, it's rarely used in formal documents.

As an example, 妻子 and 老婆 are both Chinese words for "wife". 妻子 is 书面语 while 老婆 is 口语.