How to Remove Broken Glow Plugs


Intro: 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

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

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

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

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

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!

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

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.


Very useful. I was considering buying a diesel. How is the maintenance? more or less than gas? Is it worth it?
Diesel cars have about the same maintenance as a petrol body wise. Glow plugs don't go as quickly as spark plugs though as they are only used to start the engine. Once the engine is running, you can disconnect all the electrics and it will still keep running, a solenoid to shut off the fuel is used to stop the engine, it's the ONLY way. It's also the reason why you can't bump start a diesel with a completely flat battery, no power to the solenoid to open the fuel valve. Diesel engines will go on forever unless they've been run hard at high revs a lot. 150K miles is nothing to a diesel engine, it's only just run in properly by then.

Diesel fuel can be slightly dearer than petrol in some countries but with around 50% more MPG, diesel works out a lot cheaper in the long run. The ONLY real thing to be careful of is to ensure that the car you want to buy has a good quality and working Catalytic Converter, not the cheap garbage ones that Fords have. Get a nasty one and it will smoke like crazy, chances are, it won't pass the next MOT emissions test. Even ticking over, give it a boot and see if it blows out lots of black smoke before you decide to buy it.

I have a 2001 Saab 9-3 2.2 TiD and emissions were 0.5 on my last MOT and I get around 55MPG on a run and 45MPG around town, not too shabby for an 18 year old 2.2 litre engine with 200K miles on the clock. The only main thing about a diesel is that you can't expect a performance car, I've see a 2 litre cranked up to 200BHP but most factory cars have about 120 to 150. However, they pull like a train and mine will poodle around all day in second gear, up quite steep hills as well, without even touching the accelerator. Even my petrol 2.2 SRI 150 Vectra I had before it would stall on a slight hill in first unlesss I put my foot down a bit.

In all, diesels are more suited to longer journeys and especially for towing trailers and caravans. Around town all the time, they can get choked up unless you give it a good run on the motorway occasionally to blow out the c**p.

Just be a bit careful on insurance, I don't know how these insurance companies decide on the insurance classes but you can end up with a far more expensive car for insurance than it really should be. Best to check the class before you buy one to be certain. My Saab 9-3 saloon is class 21 but the same year 9-5 which is identical in every way except that it has an estate body, (Station Wagon if you're American), is class 34. Go figure.

Maintenance is about the same. Diesel may be slightly cheaper than petrol but considerably more MPG which vastly offsets the cost. I got about 40 MPG on a run from a 1.6l petrol Nissan Bluebird but I get about 48 MPG from a 2.2l TID Saab 9-3. My 1.9l non-turbo Peugot 405 went 625 miles on 50 litres of fuel, that's 62.5 MPG!

Yes it has a lot more torque, you can usually pull away on a fairly steep hill without even touching the gas pedal. One trick I used to do patrols on a site with a diesel was to put it in second, pull away and let it pull itself around the site just idling, up hills as well, not much would stop it, in first gear, it would pull itself up a 45 degree incline without me touching the gas pedal with no effort.

But you pay for it in HP so acceleration is not as good. However, saying that, new diesel cars have a lot more acceleration than older ones despite still having less HP than their petrol counterparts. My 1999 Saab 9-3 TiD SE can match a turbo petrol 1.9 Peugot 406 for acceleration quite easily. A newer model 2.2 turbo Diesel could probably leave it standing.

yo man i drive one and over all that not bad..just depends if ur burning the tires on em haahhahahah
diesel is soooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo expensive... more than 4 bucks some places
yeah, but it has more energy per dollar (like saying candles are cheaper than a 20lb gas tank)
i get what your saying but each fill up cost's so much... u could always switch it to bio deisel
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.
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.
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.
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?
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.
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
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.
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.
Then think externally: Diesel demands external systems that are less likely to fail.
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.
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.
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