The Fiat 1800 and 2100 are six-cylinder saloons produced by Italian automotive manufacturer Fiat between 1959 and 1968. Both six-cylinder models appeared in 1959: in 1963, a four-cylinder 1500 cc version was added to the range. The styling closely resembled that of the Peugeot 404 and BMC's family cars of the same period: all three were designed by Pininfarina of Turin.

1800 (1959-68)

The Fiat 1800 appeared in 1959, offered as a 4-door sedan and a 5-door Station Wagon (Family). The 1800 model had a 6-cylinder in-line engine with 1795 cc and a power output of 75 hp / 55 kW delivered through a 4-speed transmission. Its maximum speed was, depending on the version, 137 km/h (85 mph) - 142 km/h (88 mph). This was replaced in 1961 with the 1800 model B: the engine output was now 81 hp / 60 kW and top speed between 143 km/h (89 mph) - 146 km/h (91 mph).

2100 (1959-61)

The 2100 was a version with a bigger six-cylinder engine. In autumn 1959, the 2100 Speciale was introduced with a lengthened wheelbase and different front grille. The Speciale was used by diplomats. The 2100 was discontinued in Italy during 1961, when the Fiat 2300 became available.

1500L (1963-68)

Fiat used the body of Fiat 1800/2100 to create a new less expensive model, the Fiat 1500L introduced in 1963. To distinguish it from the 1300/1500 its name used the designation 1500L (lunga = long). The car shared with its more compact sibling Fiat's four-cylinder 1481 cc engine, delivering 72 bhp, which, in 1964, was increased in the second series to 75 bhp. A reduced-performance version was also offered for the taxi trade. This proved popular in southern Europe, equipped with a straight-4 1481 cc petrol engine developing just 60 bhp: the low power engine permitted the transport of customers in comfort and space at urban speeds, without consuming too much fuel.

This version was made also by SEAT in Spain, where no other petrol version of the Fiat 1800/2100 was ever produced. It was badged simply as SEAT 1500, since no equivalent of the Fiat 1500 was produced by SEAT. Nearly 200,000 Seat 1500s were built until 1972.

It is estimated that total production in Italy of the Fiat 1800/2100 range is 150,000.

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