Who all use use fiat engine?

Answer 1

I can't say all the car makers who use Fiat engines, but they appear in Fiat cars (of course), and some models of Suzuki, Alfa Romeo and Vauxhall. Pretty sure that some Saab models had them too. It costs huge amounts of money to develop a new engine these days, so it makes sense for the manufacturers to co-operate with each other. They then make the engines at one or perhaps two plants, and ship them around to the factories of all participating vehicle makers.

Plus VW, Porsche, Sabaru all have boxer engines.