Attempts were made to bring more advanced steam cars on the market, the most remarkable being the Doble Steam Car[45] which shortened start-up time very noticeably by incorporating a highly efficient monotube steam generator to heat a much smaller quantity of water along with effective automation of burner and water feed control. By 1923, Doble's steam cars could be started from cold with the turn of a key and driven off in 40 seconds or less. When the boiler had achieved maximum working pressure, the burner would cut out until pressure had fallen to a minimum level, whereupon it would reignite, by this means the car could achieve around 15 miles per gallon (18.8 litres/100 km) of kerosene despite its weight in excess of 5,000 lb (2,268 kg).