Glowplug Nightmare

[ed-E300DT]

One of my glowplugs needed to be replaced this week. They're original, and at 80K miles, I wasn't that surprised or concerned.
My independent mechanic could only remove one of the six. So, after I paid him for his time, I bit the bullet and took it to the dealer.

The tech at the dealer had more success - he got out four of the six. He showed me that there was a 1/2 inch of carbon buildup below the threads of the plug, which had hardened and esentially siezed them in place.

So, now my head is at the machine shop, waiting to have the #2 and #6 plugs removed. I'm looking at a bill of ~$2500 to replace parts which, by design, are meant to be replaced periodically, and which operate for about 30 seconds each time I start my car!

The dealer tells me that this is not so unusual! Sounds like poor design to me. What the dealer can't tell me is what the life expectancy of the part is, nor what the recommended replacement interval is.

Did M-B really think it was acceptable to have to remove the head to remove a glowplug?

Anyone have any experience/insight on this?

Regards,
Ed

[Fisherman]

maybe due to an aluminum head they could not remove them? frankly I am at a loss since I have never had a problem pulling gps out of a car but then all my cars are old beaters...

[TimFreeh]

I would assume its a 99 E300 turbodiesel....

This happened to a member here a couple of years ago. As I recall he had a problem with one glowplug - but I think the plug broke apart when he tried to remove it.

I've never had a problem removing a glow plug from any MB Diesel. I'm not sure if there is something about the OM606 turbo than produces extra carbon in the prechamber that causes the glow plug to "stick" in the head.

Most people on this forum don't have lots of experience with a car this new - maybe one of the professional techs can offer an opinion.

Tim

Someone once told me that spraying
water(mist with spray bottle) into the
air intake prevents carbon built up.

I don't know if that person was pulling my leg
or that he was telling the truth.

I haven't tried it so I can't confirm if it works or not.

Louis.

[P.E.Haiges]

Ed,

I go along with the theory that the problem was because of a steel GP in the aluminum head. There is an electro chemical action that causes an electron flow between dissimilar metals. This causes a solid start diffusion that fuses the 2 metals together. Carbon being soft and brittle does not fuse metals together.

I had the same problem in my 6.3 liter MB gasoline engine that had an aluminum head. It had a spark plug stuck in the head. I stripped the threads removing the spark plug and had to repair the head threads with a helicoil.

The remedy for this is to use a Never Sieze type compound on the threads and every so often loosen and retighten the GP to break any bonds that may start to form. MB certainly didn't make that an easy job on the later engines. Progress has its detractions.

P E H

[R Leo]

Originally posted by mb123mercedes
Someone once told me that spraying
water(mist with spray bottle) into the
air intake prevents carbon built up.

That's the way marine propulsion turbines are de-carboned...but, it probably takes a bigger spray bottle and an ignorant E2 to stand in the intake and perform the procedure.

[DieselAddict]

I've had some difficulty removing glow plugs on my cars because of carbon buildup which causes the plugs to rotate in place without coming out. I've found that the trick is to pull on the plugs while unscrewing them. Once removed, turn the engine for a couple seconds using the starter to blow out the carbon. Finally before putting the plugs back in, wipe the threads clean with some WD-40. This will make the plugs go in much more easily.

[ed-E300DT]

Sorry, guys. First post. Thought the vehicle info would be below my sign off.

Yup, it's a '99 Turbodiesel (US Spec). The "finest, most current diesel" M-B has to offer here, to date.

I expected it to be more bullet-proof than this. Should have definitely gone with a 100K warranty.

Cheers,
Ed

[rwthomas1]

I have to agree with PEH again on this one. I have removed enough GP's and never had a problem getting them to turn just trouble removing them once they were loosened. They always pulled out once the requisite curse words had been uttered. I put Neversieze on damned near everything, GP's included. I am willing to bet the alloy/steel mating was the problem, not the carbon. RT

[jcyuhn]

I had this happen on my '98 E300 turbodiesel. It too cost $2500 to repair. The head had to be pulled and the glowplug (one broken off plug) painstakingly removed. Normal glowplug life on this car is about three years. I had the problem when installing set #3 in January 2003. I sold the car after the repair - this problem goes beyond a quirk, it's a design defect.

The problem is not caused by corrosion, it is caused by mechanical retention of the GP via tightly packed carbon around the GP. An OM606 GP is about 6" long, vs. about 2.5" for the 617/601/602/603. The threads of the 606 GP are at the extreme top, very near the electrical connector. The great majority of the GP is in a long, narrow passageway which leads to the combustion chamber. (DOHC four valve engine with centrally located fuel injector - it's a long reach to the center of the combustion chamber.) This passageway becomes packed with carbon during normal operation of the engine. There is sufficient friction between the carbon and the glowplug to restrict its movement. The torque required to turn the glowplug exceeds the torsional strength of the glowplug, and it snaps just above the threads. Alternatively the hex flats round off - a 12mm hex head is not sufficiently robust to transfer the necessary torque. Experienced mechanics know the torque limits of the GP and quit before breaking something.

The carbon is so tight that I had extreme difficulty removing several plugs from the engine even after completely unthreading them. It was necessary to spray penetrating lubricant into the area for about two days before the plug loosened up sufficiently to be removed.

Anyways, that's my story and I'm sticking to it. I can't recommend the OM606 engine with a clear conscience, this problem is just too severe. Besides, it needs GPs so often, it's cheaper to drive an E320 with the M112 engine. The better fuel economy of the diesel doesn't offset the higher maintenance cost.

- JimY

[rwthomas1]

A 6" long GP??? No wonder the element breaks off..... What a silly design, MB should be ashamed. RT

[Ken300D]

I had no problem with siezed glow plugs during a complete changeout in the 1987 300D. These glow plugs are the same as used in the earlier 1981-1985 iron head diesels, but in the aluminum head 603 diesel. No problem turning them - a bit of a problem fully removing them due to packed carbon. But gentle persuasion and twisting loosened up the carbon. Followed that with a glow plug reamer and the new plugs went in easily.

But of course I used anti-sieze on the new ones.

I agree with JCUYHN that its more a design/dimension issue than a materials issue, based on all the descriptions I've read. Afraid I'm scratching off the later MB diesels from any future plans.

So we got "rod benders", "head crackers" and "glow plug grippers" to avoid.

Ken300D

[dmorrison]

Ed.
So you don't feel so bad

"Should have definitely gone with a 100K warranty."

I DID buy the 100,000 mile Mercedes warranty and the glow plugs are NOT covered under the warranty. So you would be paying for this anyway.

I sold my 99 E300 (75,000mi and 3 sets of glow plugs) in May and I don't miss it. Another Mercedes? It will be a 71 280SE Cabriolet. And thats the only one I will buy.

Dave

PS Just changed the glow plugs in the 82 300TD. Came out without any problems. Reamed the holes and installed a fresh set for the next 6-7 years.

[DR.DIESEL]

Yup, the carbon locks the plugs in place. When I get one that I think will break, I pull the injector and fog the combustion chamber with PB blaster overnight several times.
Usually, with some care they will come out.
However the GP can only take so much torque and when they break on the plug body above the threads, you are hosed!
That's when it is head time.
And yes, this job can be done under Starmark If you
have a good shop with a good warranty clerk and
you have a good attitude when you bring the car in.
Dr.D

[dieseldiehard]

I got to thinking, looking at my '76 project. with the old style loop Glow Plugs. They were pretty reliable weren't they? I know - if one opens up in the series connection they all go cold, but I never had one fail!
And regarding the pencil-style GP's there are two versions, one is 2 Volt the other 2.2 Volts. Does anyone know why Bosch made different voltages? For less cold climates perhaps? Or the 2.2 V plugs last longer? Just curious.

Dieseldiehard
1971 220 4-spd manual 104646
1979 300TD w/ ’85 turbo engine 290820
1983 300D 238890
1985 300TD 207980
1976 300D looking for an engine