The 1908 Model G was virtually the same as the 1907 Model G except a limousine was added to the line. One or two passenger rumble seats were available, but of a different pattern than the single rumble seat model of 1907.

There were no changes in the Model G engine for 1908, but the advertised horsepower rating was increased from 20 to 25. This was due to the newly instituted ALAM horsepower formula, which gave the Model G a horsepower rating of 25.6. Cadillac had always been conservative in horsepower ratings. The ALAM rating was also conservative, and gave the same rating to every engine with the same bore and number of cylinders. There was no allowance for design, accuracy or precision of manufacture, superior practice in fit and tolerance, etc. Although having had a voice in establishing the ALAM formula, Cadillac soon took exception to being rated the same as the least sophisticated manufacturer. Although engines were tested for actual developed horsepower, it was to be many years before horsepower curves were publicized.

The engine cylinders were cast singly, copper water jackets, detachable combustion valve chamber. The main bearings were replaceable without removing crankshaft. It had interchangeable intake and exhaust valves operated by push rod & roller cam follower on single gear driven camshaft. For engine accessories it had a belt driven fan, water pump, and oiler; splash lubrication. The engine had three point suspension. It had clockwise cranking. The carburetor was float feed controlled by foot throttle or automatic ring-type governor; jet type carburetor made by Cadillac.

The transmission was selective sliding gear, independently attached to frame