So, glow plugs are a different technology, for increasing combustion chamber temperatures enough to get fuel to ignite while an engine is cold.
Yes, sorry I wasn't clearer. Glow-plugs in diesel engines are used to pre-heat the head of a cold engine to get it warm enough for the diesel fuel to ignite. Many modern diesels do not require them, because of improved fuel-injection technology.
A sump/block heater is a different thing. It is intended to keep the engine slightly warm while it is parked, so that it starts more easily, and comes up to normal operating-temperature more quickly, which reduces engine wear and fuel consumption. PWH was referring to the old kerosine-fuelled heaters, which were usually flat "wick" lamps with a wire gauze guard, designed to be placed on the ground under the engine. I've never seen one, but my father has described the ones they used in the army. A home-brewed way of doing the same thing is rig a lamp with an incandescent light-bulb on a piece of wood, slide that under the engine, and plug the lead into a normal power-socket. Much better is a properly installed electric sump/block heater, but again you have to hook it up to an electric power-supply in your garage, car-port or whatever.
Oh, and burning kerosine releases a
lot of water-vapour. I have forgotten the exact numbers, but I think that if you burn a litre of kero, you release roughly a litre of water in the form of water-vapour, which will then condense out on cool surfaces like a car windscreen.