PeachParts Mercedes-Benz Forum - View Single Post - OM606 glow plug change

jay_bob · #11 01-21-2019, 07:41 AM

Just to be clear these are the parts of the glow plug as I named them in my discussion above.

From outside to inside you have:
the terminal - that accepts and retains the vehicle wiring harness connector, this screws on to the outer end of the electrode.

the electrode - a steel rod that is concentric with the shank, this carries the electricity between the terminal and the heating element. There is an air gap between the electrode and the shank which provides electrical isolation from the shank (which is grounded).

the nut - where you put your wrench to apply torque to install and hopefully remove the glow plug later

the threads - that generate mechanical interference with corresponding threads in the head bore to hold the glow plug in place

the shank - the steel section that extends the length of the glow plug past internal engine facilities, to allow the heating element to be in its proper location in the prechamber

the heating element - the black tip that extends into the prechamber, contains the internal resistance wire assembly, used to generate supplemental heat for starting and emissions control

This assembly is placed into a tapered bore in the cylinder head. There is a shoulder at the inward end of the bore that mates with a taper on the end of the shank. This shoulder in the bore is intended to create a seal with the taper on the glow plug shank, to keep products of combustion from propagating up the bore. Unfortunately in practice, the products of combustion can get past this shoulder and travel into the space between the shank and the bore. Since this area is relatively cooler than the cylinder, the combustion products cool and condense and deposit carbon in this space.

The point of my response above is whether anti-seize should be applied to not only the threads, but also the shank, before installation of the glow plug. Hopefully to prevent the carbon from bonding between the shank and the bore, and prevent the glow plug from seizing in the head.