Glow plugs are consumable. When the go bad throw them out. There is Jo break in process that is necessary. Take a look at the plug after you have run the engine for awhile. After you install a new plug it will tell you what your engine is doing. If the wire is distorted and clean then the engine is too lean. If the wire is black and all gummed up then the engine is too rich. You want the wire to remain in its original shape and just a little bit of oil or discoloration around the wire. That tip only works after a new plug had been installed but it tells you alot.