A more common problem was that if the water level in the boiler of a steam engine dropped too low, the lead plug in the crown of the furnace would melt, extinguishing the fire. If a hot-bulb engine ran out of fuel, it would simply stop and could be immediately restarted with more fuel. The water cooling was usually closed-circuit, so no water loss would occur unless there was a leak. If the cooling water ran low, the engine would seize through overheating — a major problem, but it carried no danger of explosion. Compared with steam, petrol (Otto-cycle), and compression-ignition (Diesel-cycle) engines, hot-bulb engines are simpler, and therefore have fewer potential problems. There is no electrical system as found on a petrol engine, and no external boiler and steam system as on a steam engine. Another big attraction with the hot-bulb engine was its ability to run on a wide range of fuels. Even poorly combustible fuels could be used, since a combination of vaporiser and compression ignition meant that such fuels could be made to burn. The usual fuel was fuel oil, similar to modern-day diesel fuel, but natural gas, kerosene, crude oil, vegetable oil or creosote could also be used. This made the hot-bulb engine very cheap to run, since it could be run on readily available fuels. Some operators even ran engines on used engine oil, thus providing almost free power. Recently, this multi-fuel ability has led to an interest in using hot-bulb engines in developing nations, where they can be run on locally produced biofuel. Due to the lengthy pre-heating time, hot-bulb engines usually started easily, even in extremely cold conditions. This made them popular choices in cold regions, such as Canada and Scandinavia, where steam engines were not viable and early petrol and diesel engines could not be relied upon to operate. However, it also makes them unsuitable for short time running use, especially in an automobile. Uses The reliability of the hot bulb engine, their ability to run on many fuels and the fact that they can be left running for hours or days at a time made them extremely popular with agricultural, forestry and marine users, where they were used for pumping and for powering milling, sawing and threshing machinery. Hot bulb engines were also used on road rollers and tractors. J. V. Svenssons Motorfabrik, i Augustendal in Stockholm Sweden used hot