OM642 Glow Plug Replacement

_{Note – thanks to Rimgaudas Lukas for permission to use this post / tips / images}

Glow or no glow?

Typically, with a glow plug fault you will be getting a glow plug warning light coming on, sometimes flashing and perhaps an engine management light. In Rimgaudas case, no codes or dash warnings, just some white smoke in the mornings.

They are notorious for snapping on removal but normally with the engine hot, they will come out. Also worth a mention is they are ceramic and if dropped, might look ok but unlikely to work.

Part numbers and MB remove / install details below

Onto Rimgaudas Lukas post;

Hello everyone want to share some info, which might be useful for someone else aswell

My S212 2010 E350 estate with 130k miles was cranking for around 4-5 seconds every morning and dropping white puff through exhaust. I did read in a forum that if you wait another 5secs after glow plug light dissappears it starts normal and yeah it did. Apparently that’s common issue due to glow plug module. But I wasn’t getting any error codes through OBD.

So decided to replace all glow plugs and glow plug module aswell.

I did some research on forums, cause was afraid to snap them

So ordered Kroil penetrating oil(which everyone recommendeds as number 1 for glow plugs), sprayed every other day for a week and on a day got engine to the work temperature.

Cleaned all area around glow plugs with air duster. 4 glow plugs came out very smooth(like a butter ), only 2 showed slight resistance, but after turning back and forth and a bit of more spray they finally gave up .

I did use glow plug bore reamer to clean all gunk out and yeah it was quite all of carbon build up.

Replaced all glow plugs and used Liqui Moly Pro line grease on a threads and body a bit. Torqued to 11Nm. Cleaned connector caps with electrical connector spray.

Replaced Beru glow plug module aswell.

It tooked me 2.5 hours in total from start to finish.

Now a car cranks and starts in a morning straight away and no white smoke anymore. Happy with a result.

All parts ordered through Autodoc , due to Mercedes haven’t got any glow plugs in stock and are on a back order.

New glow plugs NGK CZ159 (£30/piece)

Glow plug module Beru at Mercedes was £277, same Beru module in Autodoc only £94.

Part numbers

Worth noting at this point that there is a couple of part numbers listed depending on the age on the OM642 engine, essentially there is two different thread sizes. I believe the early engines had an 8mm thread and the later ones had the 10mm thread. There is also 2 different listings for the 10mm thread – different lengths.

If anyone wants me to check the original part number, please comment on the post with your chassis number and will look up for you. (or email me)

Part Numbers & Links

Not technically a part but a must for this job;

Torque Specs

Glow plug to cylinder head
– M8 Nm 11
– M10 Nm 18

MB Documents

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