Thornycroft's model range for 1909 to 1912

For this year, the company's three-car range included the 18hp, 30hp and 45hp. However the 1909 18hp was radically different to its 1908 predecessor, and less sophisticated, with a simple monobloc L-head replacing the sohc; however, like its predecessor, the 18hp had a five-bearing crankshaft. Surprisingly, in a seemingly retrograde step, the 18hp car had thermo-syphon cooling water circulation instead of a water pump. However the five-bearing crank allowed enough water space between cylinders for thermo-syphon to give adequate cooling. A four-cylinder 3,258cc engine, the new version of the 18hp engine was larger than its 2,715cc predecessor. From this year forward, all Thornycroft cars had side valves, either L-head or T-head.

1910 and 1911
The 1909 range was continued for both 1910 and 1911, but the 18hp was enlarged, yet again, from 3,258cc to 3,707cc for 1911. The London showrooms in Albemarle Street were closed in 1910.

1912
Thornycroft discontinued the big 45hp six-cylinder cars for this year, and retained the 18hp and 30hp cars. This was the last year of Thornycroft car production, because demand for the firm's commercial vehicles was high enough to justify turning car manufacturing facilities over to commercial vehicle production. A relatively small total of about 270 cars were delivered during nine years of production.