Just a little warning for anyone contemplating buying a used Merc CDI. Get the glowplugs checked before you buy.
I just bought a CDI from auction, intending to sell on. It needs a glowplug. After loads of work stripping it down to get access (very awkward), I can't shift the glowplug. Its stuck in the head and there's a risk of snapping it off.
I rang a MB tech mate of mine. Apparently what they do in the dealer workshop is use a torque wrench to undo them. If the plug doesn't free by the time a certain torque is reached (I don't have the figure, sorry) then they abandon the job and leave the duff plug in place. Obviously if the plug snaps then the head most likely will have to come off and its a VERY expensive job.
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I endorse Aprilia's comment. Have had numerous reader's letters warning of the same problem. Failed glowplugs stuck in the heads of late Mercedes diesels, usually C Class and A Class. An A Class reader was then quoted £4,500 for a new engine because it has to come out anyway to get the head off and involves a massive dismantling job.
HJ
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Sounds very familiar- just like spark plugs in Fords 1.3 engine. I snapped one of the plugs getting it out and had to send the head away for it to be machined out.
Mind you, this is essentially a 1950s engine which makes it slightly more forgivable than on a newly designed Merc diesel.
Ben
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Yes, I've had a couple of spark plugs snap in my time (and had stripped threads that've needed a Helicoil) however a snapped Merc glowplug is in a very different league. I would guess that at a dealer you'd be looking at an easy £1k job on a C-class. Don't know so much about the A-Class because I don't touch them (too many probs with suspension, steering etc.). The general design of the CDI engine doesn't help because access to the glowplugs is difficult anyway.
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Interesting problem...So if you can't undo the plug, Merc say they abandon the job? So why don't they try it until it snaps? It might just come loose, and if it snaps why does that matter if they were going to leave it in anyway?
Why do the plugs need removing to take the head off?
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Misread. The head has to come off to extract the broken glowqplug, not the other way round.
HJ
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I thought modern diesels worked at such high pressures they didn't need glowplugs.
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They sometimes need a hand to get going in extremely cold conditions.
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I have a small engineering workshop and i have had a 98% success at removing snapped mercedse glow plugs both the 10 m/m & 12 m/m(without removal of cylinderhead) it never seems to be the thread thats the problem but the element at the bottom that siezes into the head
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Why oh why do they not have an industrial process to 'coat the threads with copper grease?
With Ford plugs, a smear of grease = a new life of freedom. Nobody seems to use grease any more.
As my first car was an Austin A40 and every nut corroded, I have had a lifetime obssesion with greasing threads in the belief that in 6 years time all will be well.
Worked to perfection recently on the threads that go into the distributor casting on an MB, when I replaced the cap.
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