Hello You can hear from all CDI’s about the problems with the glow plugs. Cross through all rows: A-Class, 210 and here also Sprinter. What are the causes? Similar to the hard-baked injectors? So it can’t be made by a soot lump. Bzw. soot lumps at the glow tip, so that you can loosen the thread, but then turn off the incandescent pin? As a solution shortly before hot driving it can’t be. I guess that the soot only forms when the engines are driven too often short distance, so that the soot is stored in the (thermally unsuspicious) corners and intermediate spaces. Therefore, would it be advisable to chase the car over the highway for an hour before an exchange, so that the soot is burned away? As long as the engine starts you can still drive with a defective glow candle. How are the experiences from the practice?