Usually if that malfunctions it will feed itself with diesel and the parish with smoke and the engine might go for a run.Thermostart is the heater element in the intake manifold, it has a fuel supply from the injector leak off pipe. When the element is powered to heat, a bi-metallic valve inside opens up and allows fuel through to burn on the hot element. If this valve sticks open fuel will be pumped into the inlet manifold and pour into the cylinder through the valves in quantities greater than what can be burnt, it will then run down past the piston rings into the sump washing the lubricating oil off the liners causing the sump level to rise. Would take a good while for a lot of diesel to get through this way though. My money is on the injector pump end seal fitted backwards or a faulty replacement lift pump.