Introduction: How to Remove Broken Glow Plugs

Picture of How to Remove Broken Glow Plugs

The aluminum head 4 valve diesels are notorious for seizing glow plugs. Apparently the plugs don't seat properly at the combustion chamber end. This allows carbon to get packed in around the barrel. Over time the plugs become glued into place. The narrow neck between the hex nut and the threaded shaft isn't up to the task of untwisting the plug and it snaps off. The problem has nothing to do with the threads sticking, though the aluminum steel combination can't be helping.

If you have a broken off glow plug, you are faced with a choice:

A: Remove the head and take it down to a machine shop to have the plug machined out

-- OR --

B: Make a simple puller to yank out the plug.

This page describes how to do (B)

Step 1: Tools, Caveat & Initial Work

This instructable is based on my DIY page on removing glowplugs from OM606 heads '''HERE'''. As such, if you are pulling a different plug you will need to adjust the tools and dimension a bit. The basic method should still be valid.


  • vice grips
  • drill motor
  • 1cm drill bit (13/32" is just right, 7/16" might be too big)
  • M6 x 1.0 Tap and drill set
  • hardened M6 x 1.0 bolt, at least 6cm long
  • hardened M6 nut
  • assortment of washers
  • a 13mm X 3/8" standard depth socket
  • patience, lots of patience, heads are very expensive replacement parts

Vice grips will do nicely. This part of the job is brute force. Just tear the off the hex part and then clamp onto the electrode and lever it out. The electrode is a good 4cm long and can be welded in there pretty well. I've had to use a pry bar to pull the electrode out. It has to come out for the next steps.

< no picture for this step ... sorry >

Step 2: Freeing the Threads

Picture of Freeing the Threads

Drill out the threaded portion of the plug. Use a 1cm/.4" drill bit to drill the first 15mm of the snapped off plug. This gets you through the threaded portion of the plug. Now the plug can be pulled straight out, rather than needing to be turned. If you drill straight along the axis of the plug you will leave the threads of the plug in the head. The head will be undamaged. Blow out the chips.

Step 3: Drilling the Body

Picture of Drilling the Body

Drill out the hollow part of the plug with the 5mm drill from the M6 Tap set. Go in at least 35mm and not more than 45mm, as measured from the surface of the head. Blow out the chips.

(All units measured for 24 valve OM606 engine)

Step 4: Tapping the Body

Picture of Tapping the Body

Use a M6x1.0 tap to make threads on the inside of the glow plug body as far in as the tap will go smoothly. Whatever you do, don't break the tap in there. Take your time. Blow out the chips. (picture shows larger tap, use a M6 for this step)

(Again, measurements relate to the OM606 24V)

Step 5: Building the Puller

Picture of Building the Puller

Thread the M6 nut onto the M6 bolt. Then stack some washers on to the bolt and thread it as far as it can go into the (now threaded) glow plug. Just get it snug, no real force is required.

Step 6: Pull the Plug

Picture of Pull the Plug

Turn the nut clockwise so that it gets further away from the bolt head. This will force the plug out of the head. The first real resistance will be firm. After the grip of the carbon gunk is broken it will move easier. Then it will stop moving. This means that the plug is jammed up against the washers. Unscrew the puller and pry out any bits (thread rings, etc) that are easily removable.

Reassemble the puller with a 13mm x 3/8" socket instead of the washers. The hollow formed by the socket will allow the plug to move further out of the head.

Step 7: Success!

Picture of Success!

When the bolt head starts to turn, you will have pulled the plug out far enough that you can yank it out by hand. This is what you should see:

Step 8: Cleanup & End Result

Picture of Cleanup & End Result

Suction out the chips. Then, insert some wadded up tissue paper into the hole. Now you can clean up or repair the threads. If you were careful the threads should be good and you can install a new plug. If the threads are damaged, install a Time-Sert or Heli-coil (M12x1.25 x 15mm). Remember to ream out the glow plug hole (Klann KL-0369-13)

As an experiment, I've chosen to coat the entire body of the plug with Hylomar HPF. Aside from sealing the nose and threads this sealant is fairly temperature stable and may fill up the space that would otherwise fill up with carbon. We'll see in 50Kmiles or so.


inkblotz (author)2017-12-07

WOW, excellent job. Thanks for posting. Any updates on the ability of Hylomar HPF? Perhaps we can discuss it in June.


brianpxbd (author)2014-06-03

Thank you for a very good suggestion and the clear explanation.

It is a great method, but if I have to do this I think it would be nearly impossible, as I have a J5 Camper van and the motor is horizontal mounted, meaning that the glow plugs are on the rear side of the engine and partly masked by the engine firewall. Greetings Brian

LinuxH4x0r (author)2008-04-29

Very useful. I was considering buying a diesel. How is the maintenance? more or less than gas? Is it worth it?

ilikeadabox (author)LinuxH4x0r2011-03-06

yo man i drive one and over all that not bad..just depends if ur burning the tires on em haahhahahah

iKill (author)LinuxH4x0r2008-04-29

diesel is soooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo expensive... more than 4 bucks some places

LinuxH4x0r (author)iKill2008-04-29

yeah, but it has more energy per dollar (like saying candles are cheaper than a 20lb gas tank)

iKill (author)LinuxH4x0r2008-04-29

i get what your saying but each fill up cost's so much... u could always switch it to bio deisel

LinuxH4x0r (author)iKill2008-04-29

yep, thats the best option

leebryuk (author)LinuxH4x0r2008-05-01

Nope, the UN recently claimed that Biofuels are considered a crime against humanity by causing shortages of food. It's been something that's been predicted for a while, but it's been made worse by the whole US market woes rippling throughout the world.

BBC Article on UN

Linux, you are right that you do get more bang for your buck and diesel is therefore more cost efficient per mile driven.

Mepains point is sort of like saying that having a bigger gas tank is inherently worse because it costs a lot to fill up at each refill, irrespective of overall efficiency per mile traveled. By his point, you could "eliminate" the diesel cost disparity by halving the size of VW Jetta tank and therefore making it "cost less" per refill.

So, go feel free to buy a modern diesel and have a nice time. On the other hand, modern compacts (Honda Civic, Toyota Corolla) can achieve around 40mpg if they are driven by sane human people. My 2000 Saturn SC1 consistently (we are talking over years) had a personal mpg city 28/interstate 40. Use the cruise control judiciously while on the Interstate, pace yourself behind a slower line of cars and in town, don't accelerate quickly, especially if you are heading up to a stoplight again. Sit back and relax while you drive.

And purchase a standard (stick) transmission. It makes a big difference.

LinuxH4x0r (author)leebryuk2008-05-01

Wrong! Thats talking about growing fuel. Waste veggie oil is actually a good thing. You can mix it with a few other chemicals and produce bio fuel.

Besides, the UN is BS!

UN sucks

tech-king (author)LinuxH4x0r2008-05-02

its worth noting that diesels have a less horsepower than gas and lower top speeds, but more torque. this is because, in order to get the high compression ratios needed, they have long, narrow bore cylinders.

membrane (author)tech-king2008-05-05

The less horse power remark used to be true but the newer CDI turbo diesels are almost the same as their gasoline counter parts and you can hardly tell it's a diesel when driving it.
Here's a good example of a modern diesel it actually can outperform many gasoline cars.
You'll be very hard pressed to get 295lb/ft of torque in anything less then a big V8
let alone a 2.2l i4 gas engine.

tech-king (author)membrane2008-05-06

as i said, diesels have more torque and less hp. a turbo does help, but there still is a gap. giving torque ratings just proves my point. how many hp does that engine give?

membrane (author)tech-king2008-05-06

Well to produce what you would notice as acceleration takes torque. An engine that has it torque peak at 2800rpm will feel much more powerful then an engine with it torque peak at 4700rpm even if they are producing about he same amount of power. A horse power is not always the same it's also is important where in the power band the power is generated if it's around 7800rpm it's pretty much useless for street driving and as far as most users are concerned. Also the 2.2l CDI produces 170hp which is very impressive for a small engine and this is with a much flatter torque band then most gas engines so it'll be faster then a 200hp gas engine in the same car. It will out perform 90% of the gas i4s in similar vehicles out there.

tech-king (author)membrane2008-05-06

torque is acceleration. all around performance is horsepower. so it really does not matter that it has more torque; all diesels have high torque engines. and most engine peak both torque and hp between 2800 and 3800 rpm. 170 hp? and the displacement is 2.2 liters. thats about average for gas i think

Esmagamus (author)tech-king2008-06-05

And you know something? Americans just have something against diesel. Europe trusts diesels for decades. And European or Japanese diesels are usually hard to break. The fact that diesels must handle a lot more pressure forces car makers to build them better than gasoline engines.

leebryuk (author)Esmagamus2008-06-05

It's a preference. Diesels drive differently than petrol engines. Diesels are also a premium in cost, usually about $2,000. People aren't to happy about paying all that extra dosh for a machine that will get them to the same place. Also, the US has stricter emissions than Europe. European diesel cars wouldn't come close to passing US emissions. Also, the cost of petrol/diesel wasn't that important until recently so there was little reason to spend an extra 10% on the price of an identical car. And, as one who works on cars and peruses junkyards often, it is rare that you have an engine that internally fails. It's a serious of failures, usually in the fuel injection systems or other externals. I have never owned a car that failed internally. I have over my years only come across one car that failed internally, and that was because it was very poorly assembled. Otherwise, the record is pretty close.

Esmagamus (author)leebryuk2008-06-06

Then think externally: Diesel demands external systems that are less likely to fail.

leebryuk (author)Esmagamus2008-06-06

To the contrary, the systems for diesels are more complex. There are obvious things (such as the glow plugs.) However, in order to get rid of that diesel clunking sound, diesel fuel is injected at several points in the compression cycle. It is a more complex system. Lifespans of cars are not determined by internal engine components. They are dictated by the small things that fall apart over time. It all adds up, along with increasing maintenance (up to a point) and it reaches a point that owners will no longer tolerate. I see diesels in the junkyards as well. And they are the same age as the petrol cars.

fondyin (author)leebryuk2010-12-09

You are right the fuel system is more complex. But the trade off is if set up right it can outlast a gas engine. Fewer people working on them means fewer people even know how they work and it is more of a mystery to them as how to even maintain them. I pulled one out of the junkyard about a month ago and spent a whooping $40 dollars to replace filters and a few crush rings and a few more bucks to clean bacteria growth out of the fuel system. It ran like a champ. This was a supposed blown engine by the way.

Esmagamus (author)leebryuk2008-06-06

And about the emission standards: Americans are still only 5% of the world population and make 25% of the world's air pollution. Think about it.

leebryuk (author)Esmagamus2008-06-06

I did, and I don't get it. Emissions and safety are still more stringent in spite of our dismal petrol economy.

Esmagamus (author)leebryuk2008-06-09

Well, probably some activities aren't regulated. That should be the problem. Cheap energy leads to waste.

tech-king (author)Esmagamus2008-06-10

1) i am not american 2) at no point did i say diesel was bad; i merely stated the facts. diesels are more complex (more things to break), have lower power-to-weight ratios and less horsepower. they have more torque. some have cold starting problems. they sound terrible at idle. the fuel smells awful. they cost less in fuel bills supposedly. the emissions also smell bad.

fondyin (author)tech-king2010-12-09

Disels actually have less things to go wrong than gas engine. The primary difference is the lack of a ignition system to run the egine. Older diesels can actually be run without an electrical system at all. The diesel knock is the rough sound at idle. There are several diesel companies that have all but eliminated it over the past decade. It is just that most of those aren't based here in the US.

Derin (author)tech-king2008-09-06

but i like the idling sound!

mcreynol (author)tech-king2008-06-10

The "diesels are noisy, stinky and slow" belief is fed, paradoxically, by the fact that the newer diesels are quiet, clean and quick. Standing on a street corner the average person notices a car clattering and sees a sooty diesel. They fail to notice the new tech diesel purring right next to it, probably on the assumption that it is a gasoline engine. The newer diesels are by no means more complicated than gas engines and are inherently more efficient. The latest high pressure injection systems had their growing pains but that is over now. Glow plugs are rarely needed these days. All it takes to start is one or two working ones anyway. That leaves N-1 or N-2 spares.

leebryuk (author)mcreynol2008-06-10

The perception of passenger diesels as being inferior comes from the initial imports of the Mercedes and Volvo diesel cars. They were stinky, noisy and had very different driving characteristics. The turbos didn't do their job very well. Also, GM tried their hand at re-engineering gasoline engines to diesel combustion. They were unreliable and made a hell of a racket. All of this left a vivid memory in the public mind. Modern diesels are more complex and require a higher degree of machining to run properly. There's nothing wrong with that. My old beetle was a very simple machine and it drove like hell. My saturn was far more complicated and was a joy to drive. My brother's modern Cadillac is extremely complicated relative to the two and I cannot think of a more pleasant car to ride in.

carpespasm (author)leebryuk2008-08-03

I just wanted to see this thread get skinnier and skinnier.

fondyin (author)leebryuk2010-12-09

You are right in some points. The only thing is diesel burns cleaner than gas. The black smoke is mostly inert gas that doesn't breakdown into acid rain like gas engines. Most americans see black smoke and think it s bad. I have owned several diesels over ther years as well as gass burners. I am also a marine technician that owns his own marine repair company. I am factory trained to work on several types of enines. All the info is out there if people just bother to look for it.

fondyin (author)tech-king2010-12-09

Diesels use compression to ignitite the fuel. Glow plugs are only used for starting. That is why diesels are heavier than gas engines. Most diesels don't even need glow plugs to start except for temps under 40 degrees.

Another difference in diesel and gasoline engines is type of HP rating used. Indicated (which is used for gasoline egines) is the max that engine can produce even if it is for only 2 seconds. Rated HP( which is used by diesels) is the amount of horsepower the enignne is built to produce under a constant load.

Horsepower is torque times RPM. Higher the RPM's the more horsepower that can be produced.

Esmagamus (author)tech-king2008-06-05

That is also the most fuel-efficient engine in common production cars.

Derin (author)membrane2008-09-06

we have TDI with no red letters like T DI or TD I as i like to callthem.(damned spacebar and damned lemonade about to fall off table)

leebryuk (author)LinuxH4x0r2008-05-01

You agreed that biodiesel is the best option (see conversation with Mepains). Bio diesel has at least a certain percentage from plant sources. The primary source for biodiesel in the world is palm oil from Southeast Asia and Pacific Rim. Crop area that was once used for rice is being converted into palm oil tree plantations. This leaves less room for rice and other staples to be grown. This then increases the price of these staples making it difficult to buy enough to eat. Another major source of biodiesel is soybeans. Soybeans are used in animal feed to improve growth (soy beans are high in protein as well as oil.) However, the beans grown are higher in oil. There are more of them being grown, which takes away from the land available for corn and wheat. This raises the cost of corn and wheat. The percentage of income for a person in the West for food is usually less than 10%. In the devoloping world it runs up to 70%. Think about it, 70%. In response to using waste oil, it's a nice quaint idea. However, you can never ever have enough Chinese restaurants churning out enough used oil to make a significant dent in the fuel consumption of the US. If we moved to a commercial collection system, it would take trucks and chemical plants to refine and then redistribute this oil. This in turn burns fuel, be it fossil or veggie derived oil. Used, processed veggie oil is even worse. It takes several chemical reactions to process it to make veggie diesel. These chemicals don't come from biodiesel. There is a cost and benefit to everything. You have to way them each and see how it balances out. *** The UN is comprised of member nations. Most are very reluctant to have any countries internal affairs altered because they worry, right or wrong, that they can be next. The US stopped shipment of several key pieces of military hardware that most likely would of stopped the war from proceeding. It is the collective nations of the UN that are at fault, not the UN as a whole. And it is not logical to state that the failure in Rwanda negates all other actions or studies from the UN. I had a friend who served with the UN forces in Rwanda and he said it was easily the worse thing he saw in his long career. They wanted to fight, but were not allowed. Whenever we talk about it, the one thing he remembers is the smell above all else. History is replete with atrocities that are mind numbing in scope. You should study more about genocides. You can learn a lot about humanity, international politics and what it takes to end those sort of wars. Take some classes on the Holocaust and other genocides in college. You'll be stunned, for reasons beyond the obvious.

netbuddy (author)leebryuk2009-01-26

Sorry but you do not need to have "Used" veg oil to convert a diesel car in to a bio fuel car.

membrane (author)leebryuk2008-05-05

Also biodiesel can be made from algae it's a better option then hybrids most of which are just marketing PR stunts. Though placing hybrid drives in heavy vehicles is a good idea but you do pay a price for starting and stopping the engine more often in a parallel hybrid in reduced service life. Though preoiling the engine before restart if it's been shut down for more then 10 minutes would help prolong engine life. A series hybrid would not have as many start and stop cycles as a parallel hybrid so this becomes a lot less of an issue. Also a diesel will still be running long after that prius's battery pack and engine have failed. I seen VW and Mercedes diesels that had a million miles and still ran well.

membrane (author)LinuxH4x0r2008-05-05

I agree this Jean Ziegler guy just doesn't know his facts . Energy is a huge cost in food processing and distribution the cost of oil and natural gas have a much larger influence then the cost of the farm commodities themselves. Even if all the land used for biofuels was converted over to food production and all live stock gotten rid of food prices would still be almost as high because the procession and transportation costs will remain unaffected and this is over 83% of the real costs. The only thing it would accomplished is force more dependence on foreign oil and harm the livelihood of farmers. Also most famine is from two things displacement via war and economic inequality.

leebryuk (author)membrane2008-05-06

Yes, the UN certainly is ignorant of issues regarding food, poverty and famine. BTW, if we converted every inch of airable land in the US to ethanol farming, we would still only be able to supply 20% of the US need for ethanol. The answer is a reasonable one. Conservation and more efficient use of transportaion is the way.

membrane (author)leebryuk2008-05-05

Biofuels are not the primary cause of the high food prices that is oil company propaganda. The real and only cause is simply high oil prices and transportation costs. Farm commodities only account for 17cents per food dollar the rest is processing and transportation cost which largely depend on energy costs. Jean Ziegler may be an activist and thinks he's on some mission to save the world but he knows nothing about farming,food production and transportation. BTW there is more then enough food to go around but where things break down is in distribution. Not addressing the high energy cost will make more people go hungry as this effects food cost directly. This is a classic example where one can do more harm then good even if they mean well if they do not understand the cause of the problem.

nature223 (author)iKill2008-05-01

yes,but you normally ger an added 5-10mpg over a comparable gas it works out as a added range thing. or run Bio/Veg Oil..and really run it cheap

Esmagamus (author)LinuxH4x0r2008-06-05

Are you kidding me?

Charger_06 (author)LinuxH4x0r2008-05-01

Diesel car get way better MPG than gas. Most get 45-50 Mpg.When comparing gas prices you pay about the same as far as, how far the gas and diesel goes!

unaffiliatedperson (author)2010-11-20

nice i had similar ideas about removing a stuck battery in a mini maglite. but it failed

kington99 (author)2008-05-01

would a normal broken stud extractor not be suitable for this job?

mcreynol (author)kington992008-05-01

Not likely. I presume you are talking about an "Easy Out" type of device? The stuck plugs are ~60mm long, the walls are quite thin and broken off flush with the head. An EZ-Out would just spread out the outer part of the plug and quite likely break off.

kington99 (author)mcreynol2008-05-01

ah fair enough, I didn't realise the plugs were of such a fragile construction.

blaminack (author)2008-05-01

This is exactly the kind of thing that brings value to this site for me. Something that is extremely useful that I have no idea when I may need. I don't own a diesel but if I did I would want to know this! Thanks to the knowledge.

Mr. Rig It (author)2008-04-30

Nice Instructable, good informative steps, well written. Good Job! you get a + plus

GorillazMiko (author)2008-04-29

I knew LinuxH4x0r would comment on this.

Nice job!

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