Diesel engines are generally provided with an injection pump which takes Diesel oil from a tank and delivers it into injectors in the engine, after having passed it through a filter.
When the Diesel oil is at a temperature less than the temperature at the limit of filterability, which is, for example, at about -10.degree. C., the Diesel oil deposits flakes which clog the filter. The engine can start when the temperature of the Diesel oil is between the filterability limit temperature and a flow limit temperature, which is, for example, -18.degree. C., but operation is interrupted when the filter is clogged.
Various solutions have been proposed to ensure that the engine can be used when the temperature of the Diesel oil is between the two limit temperatures indicated above. In particular, it is known to provide a Diesel oil heater which employs the heat recovered by the water cooling the engine; the engine having started and heating up, the temperature of the Diesel oil rises and becomes higher than the filterability limit temperature, with the result that there is no deposit of flakes and any deposited flakes redissolve in the Diesel oil; any risk of clogging of the filter is avoided.