Just wondering if anyone here ever attempted heating the aluminum head around a stuck glow plug with a torch then apply candle wax rather than pb blaster or some other penetrant.
I have used this method in the past with success on seized bolts. the melted wax seems to "wick" into the threads similar to solder flux when soldering copper pipes.

Get the engine warmed up. Ok to run without the manifold to get it warm, use common sense and don't let anything get sucked in.

Try AeroKroil penetrant, nothing else compares.

I would get it warm, pull the manifold, and apply the penetrant in the evening (like Friday night). Then Saturday morning start it up again and let it get heated up. Then hit the plugs again with the AeroKroil.

Wait a few minutes then use a battery operated impact to free the plugs. I have read many threads on this and this seems to be the best tactic. Don't use a gorilla 3/4 inch air compressor impact, just a little 1/4 inch battery drill type with a socket adapter. The impact has several benefits. One is that the many small shocks are better at breaking the plug loose than the constant force provided when you turn the ratchet. Also applying force with a ratchet tends to be off center due to the physics involved, this ends up applying an uneven force to the plug and I suspect this is what really ends up snapping them off.

Also don't forget to pick up a tube of Anti-Seize for the new plugs. And be sure you have either the official reamer tool or use an appropriately sized drill bit smeared with grease. Use No Power Tools on the reamer!!

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2014 ML350 Bluetec (wife's DD)
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both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech

Excellent advice Jay-Bob,
I just bought this car with all service records from previous owner and came across one of the invoices from 2012 that stated #1 glow plug was replaced and the remaining 5 were seized and not replaced at owners request. I called the Mercedes service center that has maintained this car and the guy I talked to was very familiar with it, he said previous owner was very very meticulous with the car but opted not to spend the money to change the glow plugs because the car was stored winters. he also told me what they do is set a torque wrench to the correct value for glow plugs and attempt to remove the plugs and if they do not come out the head comes off and goes to a machine shop were they get cut out with an EDM machine, then the new plugs go in and the head goes back on and $4000 later you are good to go!!

Aerokroil has been ordered and on it's way.
Thanks again for your help and wish me luck!

Best advice is right here and the method I used to remove the glow plugs on my now sold '98 E300. If they still don't wanna come out, tighten it with a ratchet and back it off again. Rinse, wash, repeat!

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Only diesels in this driveway.
2005 E320 CDI 243k Black/Black
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jay_bob, I wanted to simulate removing a seized glow plug before attempting it on my car. I took a piece of aluminum, drilled a hole a little larger in diameter than the small end of the glow plug (the tip that glows) then drilled down with the tap drill staying above the bottom of the block for the glow plug to seat at the bottom and finally taped the top and removed all cutting oil.
Using an oxy acetylene torch adjusted with a yellow flame, I covered the glow plug with soot, then screwed it into the block as tight as possible without risk of breaking it (I do not have a torque wrench yet) then applied Aerokroil and let soak for three days. I put the block in a vise and hit it with a small 3/8" air operated "butterfly" impact wrench (80 ft/lbs. max.) turned way down. I turned the wrench up half way, I'm guessing 40ft/lbs. and the glow plug would not budge. I tried this several times letting the impact wrench hammer for at least ten seconds at a time. the next thing I did was to heat the block up with the torch getting it just hot enough where I could hold it in my hand without getting burned. I hit it with the impact wrench and the plug spun right out!
Your idea of keeping the engine warm is excellent advice.
I might try this test again with the block cold and turning up the impact wrench a little at a time just to find the breaking point of the glow plug then turn it back down somewhat when I attempt this on my car with the engine warm.

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You are the first one that has posted that it works.

I am inclined to think it would work where the treads are corroded but not if they are siezed due to Carbon leaking past the sealing area (the plugs don't seal on the threads).

Note use some never-sieze type compound at least on the threads of the new Glow Plugs to prvent the corrosion.

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84 300D, 82 Volvo 244Gl Diesel

Well gee, I was a mechanic for 18 years and never had any one say melted wax would help loosen nuts and bolts! Not even the old timers.

One of the reasons I read this forum is to learn new stuff and today I did.

"My favorite trick for removing rusted NPT pipe plugs from cast iron is to heat the surrounding iron, then melt a candle on the threads. Paraffin will wick into the threads and act as a lubricant. Be sure to use a snug fitting, proper sized socket. In this example I used a special female square drive socket that fits the square on the pipe plug."

"Be sure to first clean off all the penetrating oil and only use open flame in areas
safe to do so. ... iron is to heat the surrounding iron, then melt a candle on the
threads. Paraffin will wick into the threads and act as a lubricant."
Removing Rusted Bolts

The Art of Removing Stuck Nuts and Bolts - DSPORT Magazine

Who has bees wax in their tool box ? [Archive] - The Garage Journal Board
"Recently I retired from going to sea for 30 years. I sailed deep sea as an engineer. Every ship had blocks of bees wax in the machine shop. It is for sale in the Mariner's Catalog.

Steam engineers, even before the Cival War, melted wax on hot stubborn nuts and bolts. It would seep into any thread or frozen up tight space. This was used way before Blaster and Liquid Wrench was invented.

I often heat up things gently and then put the wax to it. Some poor guy on a different thread was fighting a sheared off water pump housing bolt. I would have heated the bolt head with a small flame and let the wax do all the work."

I am afraid this old trick is not used very much anymore except by seaman that I've worked with. I have found it in a few old hardware stores and also on the internet. Everyone that works with tools should buy a block.

FYI, the union I was in was formed in 1876. A lot of the ship and riverboat engineers were also train drivers. Anyway I hope this bees wax trick helps somebody out, preferably before they shear off a bolt or stud.

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84 300D, 82 Volvo 244Gl Diesel

I use this trick all the time. I think I learned it on the practical machinist forums, and first used it to get a frozen stud with over an inch of threads rusted into an iron block out of a ford explorer (worst car ever to work on).

Everything else failed on that bolt, but after two heat, add wax, cool cycles, it came right out. Best wrenching trick ever.

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Garage:

2017 Chevy Colorado Diesel (nanny state emissions)
2005 Volvo S40 T5 AWD, 77k
1987 Mercedes-Benz 300D turbodiesel, 4 sp auto, 156k - 28.7 mpg
1996 Tracker 4x4, 2 door, 16v, 3 sp auto. 113k - 28.6 mpg

WARNING: this post may contain dangerous free thinking.

I am surprised I was never told about this because I used to work in a Diesel Shop at a Naval Shipyard for 6 years. Also the people that I worked with and been through an apprenticeship program and there were 2 machinist right in front of us in the same building.

Lots of the stuff we worked on was badly rusted.

Then just to the side of us there was a section that was part of the “Steam Gang” that worked on the stuff steam stuff for the Ships steam turbines. I mean 2 guys would spend 2-3 hours trying to remove the large Bolts with a Sludge Hammer and a Slug/Striking Wrench.. And there was 6 or more Bolts just on one side of the items they worked on. It was a daily struggle for them.

I once spoke with my Forman and said that if replacing the Bolts costs less then the labor to remove them they should cut the bolts off and buy new Bolts. But, I doubt if he ever looked in to that as it was not our shop.

So who knows if some Wax might have helped as they were there with Torches heating the stuff up. I know they used a lot of Penatrating Oil.

By the way that was Tax money going to pay those guys to beat off the Bolts.
　

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84 300D, 82 Volvo 244Gl Diesel

+1 on 'its not the threads that seize' - been there done that. The carbon below the threads seizes the GP. The neck snaps off below the threaded body. Hence the strong advise to use Neverseize on the GP.

I was under the assumption that the threaded portion of the the glow plug was the area that becomes seized. Now that I have a better understanding of where the carbon is actually building up, that changes everything.
If I understand correctly there is a chamfer near the bottom of the glow plug body and the electrode protrudes beyond that approx. an inch or so.
The chamfer near the bottom of the glow plug body seats at the bottom of the pre chamber in the head where it has a chamfer at the bottom as well.
If the bottom of the glow plug is not seated at the chamfer, carbon will migrate and impact the length of the glow plug body up to the underside of the threaded portion.
If I am correct, this would be like trying to remove a bolt that is embedded in concrete!?

Another option to keep the engine warm while you work on it is to plug in the block heater. (Obviously this assumes your car has one and the required cord.) This is especially helpful if you're changing all the glow plugs and thus taking longer than just one.

Jeremy

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"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
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Santa Rosa population 176,762 (2022)
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"Oh lord won't you buy me a Mercedes Benz."
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Yes it can either be corroded threads or carbon build up or both of them combined.

From the number of posts corroded threads seem to be the most frequent issue.

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84 300D, 82 Volvo 244Gl Diesel

Next time I come across the issue (twice so far) going to try another theory by building small clay walls around each injector well. The idea being to fill with small amount of solvent (bio diesel) then drive a for a month or two.

What's the chances of it working through to carbon affected areas?

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David


1996 Mercedes S124 E300TD - 129k - rolling restoration project -

1998 Mercedes W210 300TD - 118k (assimilated into above vehicle)