I have a problem with the glow plug system of my 240D, 1980 Mercedes. I already changed all the glow plugs loop type, the relay and checked all the glow plug lines. I checked the alternator and is OK and installed a brand new battery. The car works fine about 2 weeks, and then burned one plug. I changed it again and after 2 weeks burned another plug. Then I changed the fuse for a 30 Amp one to avoid burning the plugs and again burned the fuse. The only thing that I noticed is that the system burned the plugs after I drived more than 40 or 50 Kms. Then when I tried to start the car, one of the plugs or the fuse are burned. What could be the problem?