Background, I have had this car for about 5 years. I replaced the GP wire harness about 4 yrs ago, and the glowplugs about 1.5 yr ago.

About a month or so ago the GP indicator light started being erratic- not coming on when cold and then coming on for a short time until the motor warmed up. About a week ago it stopped working altogether and cold starts were very hard (temps in 30s at night).

I followed the tutorial on Diesel Giant and tested the glowplugs for continuity at the relay- found one was bad #5 cylinder. All other tests of the relay were fine- power at relay 11.8v and power to GP connector good on all cylinders at 11.6v.

Pulled the bad one last night, and put a new one in after I tested it for continuity and also put 12v on it and got nice red hot tip. Engine was still warm last night so I couldn't test it.

This AM I get up and try it- no GP light and hard start (42F ambient temp). Still get good current at relay and GP harness plug, and all GP test good for continuity between .4 and .7. Odd thing is that after starting up, the GP light on dashboard will come on for a short time.

Is it the relay? Did I miss anything?

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1995 E300 diesel

If relay tests OK....there is power to plugs, it sounds like you still have one or more bad glow plugs.

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-- Chris

'95 E300, 216k miles, Silver Surfer
'05 E320 CDI, 138k miles
'07 S550 4matic, 69k miles

Gone but not forgotten:

'76 300D, 350k miles?, SOLD in 1995
'75 240D, 300k miles, SOLD in 1991

but they all test ok for continuity at the harness plug - is it possible that one is still bad and that I must pull them all and individually test them?

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1995 E300 diesel

Can you hear the relay click off after the car is running for 90-120 seconds? If it's staying on or malfunctioning, it could be burning out your glow plugs.

Did you use Beru glow plugs or some other brand? Mercedes uses Beru at the factory. I've purposely destroyed several Bosch and Beru to see how much it takes to twist them apart. Berus are much stronger than other brands including Bosch.

Ohm meter check isn't as accurate as visually evaluating the glow color and glow location with the glow plug out of the head and directly connected to a battery via jumper cable.

You're luckier than most with this engine. Lots of owners bust one or two of the glow plugs removing them.

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2009 E320 Bluetec 117,000
1995 E300D 306,000 Sold
1996 Ford Taurus LX 130,000 Sold
1985 300TD Still 225,000 Sold
2016 Ford Fusion 24,900

I got Bosch from the local indy shop. Yes I can hear the relay click off.

Ug, so I guess I am removed the intake manifold and manually testing all of them.... glad I got a spare one.

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1995 E300 diesel

I would strongly recommend you ream the gp holes with the proper tool and clean the tapered part of the hole and the tapered part of the plug. I also strongly recommend you use Beru plugs and the Beru anti-sieze grease on the threads and torque to spec.

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2009 E320 Bluetec 117,000
1995 E300D 306,000 Sold
1996 Ford Taurus LX 130,000 Sold
1985 300TD Still 225,000 Sold
2016 Ford Fusion 24,900

I did that 1.5 ago when I replace all the GPs...

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1995 E300 diesel

Well, any time a Glow Plug is out it is OK to ream the Carbon out.

As nice as the Glow Plug Light is if your Engine is staring up OK that indicates that part of the Relay is working.

I hand One Glow Plug that was OK with the Ohm Meter but when I pulled and tested it was getting hottest in the center of the tip of the Glow Plug. You really need to go by the Symptoms.
If the GPs Ohm out OK and they are getting they required Voltage but you still have Symptoms of bad Glow Plugs you won't know till you pull them all and check them on the Battery.

As far as the Beru Glow Plugs go it is nice that the don't snap off as easily as the Bosch ones. But, the ones that came with the Engine OE are the ones that People are snapping off because they have been in the Engine for a long time.

If when you installed the Bosch Glow Plugs and used a Never-seeze type compound on the Threads or that Beru Glow Plug Grease; I think they said on the whole body of the Plug; the only reason left for them to get seized in the Head is if Carbon got past the sealing area/shoulder on the Glow Plug.

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84 300D, 82 Volvo 244Gl Diesel

OK, so the continuity test is not a guarantee. I will pull the remaining ones until I find more problems.

Where do I find a GP reamer for my motor? Come to think of it I didn't ream them out the last time, I did clean out the intake ports though....

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1995 E300 diesel

If it were me I would clip onto a glow plug with a voltmeter extension line if needed. Watch the actual voltage being fed the glow plugs with a cold engine during the run up to starting.

At this point you do not know if it is remaining on when needed. It kind of sounds like it may not be.

OK, so I got a reamer from Mercedes Source and set to pull them tonight. I got 5 out, the #2 plug is stuck. It spins but is not coming out. What are my options? see photo.

The other ones came out relatively easy, they were replaced about 2 yrs ago. Not a terrible amount of carbon on the others. This one "may" have had the plug come loose, I'm not sure if it came off when I was pulling the adjacent one.

Attached Thumbnails

 

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1995 E300 diesel

Were you able to back the plug out to expose some threads on the glow plug body or is it broken and spinning? If threads are visible, then carbon on the tip is preventing removal. If it is broken and spinning, you are in deep.

If you were able to back it out and threads are visible, then use this tool to get it out. Don't mess around. Just buy this tool, go slow and you will get the plug out. Spray plenty of kroil or other penetrant in the hole. Google this: CTA Tools 2820 Diesel Glow Plug Remover. I used this on my 606 with success. I destroyed the hinged nut by the end of my job indicating that the plugs were royally stuck.

Use only short-handle ratchets to remove glow plugs from the 606 to reduce the risk of over-extract-torquing. (just made that up)

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2009 E320 Bluetec 117,000
1995 E300D 306,000 Sold
1996 Ford Taurus LX 130,000 Sold
1985 300TD Still 225,000 Sold
2016 Ford Fusion 24,900

what about just using an easy out as opposed to the method stated here?

PeachPartsWiki: Broken Glow Plug Removal

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1995 E300 diesel

I just tested the plugs for resistance, and they all passed including the one that is stuck so I think I am going to reinstall the others and just go with it for now.

Is it necessary to put a new intake manifold gasket on? the existing one looks fine.

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1995 E300 diesel

as connermn said - use that tool, I had a mechanic loan me a socket looking tool that actually worked like a slide hammer if I wanted to (he said it was for some chev diesel), but I used it in the same principle as the split nut tool. It literally pulled the plug straight out.

Get the engine really really really hot, I even removed the fan and attempted to loosen the plugs with the engine running. Engine temp was registering 105 (high spd electric kicked in) - They still squeaked. I did get them replaced - took me a whole day. Be sure to ream the holes and slather some copper antisieze on your new BERU plugs before you install them.

There are some crafty mechanics in some other countries who have made tools that are nothing more than correctly placed pilot holes for drilling etc for these glow plugs. They mount on the intake manifold bolt holes. if I can find a picture I will post it here.


precis - dont attempt OM606 glow plug service unless you have some tools like the split nut or similar to aide you, otherwise it has been known that people have trashed this engine because of GP failure.

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)