Seized Glow Plug - Cylinder 4

[59p]

Have been spraying with PlusGas for a couple of days, noticed quite a bit of it just sat around the glow plug - is this actually going down into the area and is there any issue with it being sat where it is? 

[SuperbTWM]

Yea thats good, if its sat around the thread it has the best chance of getting pulled into the threads and hopefully reduced the chances of it shearing off.

 

You may smell it as the engine warms up though

[59p]

So after a week or so of spraying the Glow Plug with PlusGas, it still wouldn't budge this morning and mechanic wasn't risking snapping it. However, the EML has gone off and not sure why! Not cleared the error code so kinda confused, anyone know why? 

[KenONeill]

12 minutes ago, 59p said:

So after a week or so of spraying the Glow Plug with PlusGas, it still wouldn't budge this morning and mechanic wasn't risking snapping it.

Remove the connectors from that plug, then spin the engine on the starter; the compression action sometimes frees a stuck plug.

Quote

the EML has gone off and not sure why! Not cleared the error code so kinda confused, anyone know why? 

I don't know which code it was but some of them do clear themselves after a number of starts and/or a certain running time.

[varooom]

Some faults codes will have learn/unlearn cycle's.  So I presume the fault has now gone away temporarily, and will return again when in time.

[ApertureS]

19 minutes ago, KenONeill said:

Remove the connectors from that plug, then spin the engine on the starter; the compression action sometimes frees a stuck plug.

Spinning an engine over creates next to no compression compared to the compression created from detonation of fuel and air. So basically would make no difference at all.

And disconnecting the plug from a glowplug aint would make no difference? Its not an ignition source and wont stop the engine from firing?

[J.R.]

36 minutes ago, ApertureS said:

Spinning an engine over creates next to no compression compared to the compression created from detonation of fuel and air. So basically would make no difference at all.

 

Not forgetting the heat generated, the OP's vehicle has had a week of combustion heat soak cycles combined with Plusgas and the glowplug is still firmly fixed, its laughable to think that cranking the engine over would free it.

Edited 22 October, 2022 by J.R.

[J.R.]

On 13/10/2022 at 12:12, SuperbTWM said:

It doesn't help that they are a tapered thread usually

Really? Are you sure about that?

 

How do they seal against combustion pressure and temperature, horsehair and Plumbers Mate or PTFE tape? 🥴

[SuperbTWM]

28 minutes ago, J.R. said:

Really? Are you sure about that?

 

How do they seal against combustion pressure and temperature, horsehair and Plumbers Mate or PTFE tape? 🥴

 

No not 100% just a gut feeling from past experiences (Last glow plug i changed was on a very primitive diesel water pump so it might of been that i was thinking of) but if you look at a glow plug there is no sealing face like you would see of a spark plug so either the thread or the threaded hole is tapered and seals by deformation of the threads or it seals further down the body in a conical seat type arrangement as they do seem rounded on the end.

 

You seem to doubt the capabilities of a tapered thread?

Edited 22 October, 2022 by SuperbTWM

[ApertureS]

2 minutes ago, SuperbTWM said:

 

No not 100% just a gut feeling from past experiences but if you look at a glow plug there is no sealing face like you would see of a spark plug so either the thread or the threaded hole is tapered and seals by deformation of the threads or it seals further down the body in a conical seat type arrangement as they do seem rounded on the end

 

You seem to doubt the capabilities of a tapered thread?

The threads are not tapered and never have been on glow plugs. Generally a M10x1.0 thread, no difference in pitch or width. They seal on a machined face.

[SuperbTWM]

10 minutes ago, ApertureS said:

The threads are not tapered and never have been on glow plugs. Generally a M10x1.0 thread, no difference in pitch or width. They seal on a machined face.

 

Which bit are you saying is the machined face? Only face I can see it sealing on is this one. 

Edited 22 October, 2022 by SuperbTWM

[J.R.]

35 minutes ago, SuperbTWM said:

either the thread or the threaded hole is tapered and seals by deformation of the threads or it seals further down the body in a conical seat type arrangement as they do seem rounded on the end.

The latter, the former is physically impossible hence the existence of pipe thread sealing compounds.

[ApertureS]

1 hour ago, SuperbTWM said:

 

Which bit are you saying is the machined face? Only face I can see it sealing on is this one. 

Exactly that. If the machined face is dirty and doesnt seal, soot makes its way up the side of the glowplug and stops at the threads. But at this point the soot literally seizes the glow plugs solid in the bore. Exact same thing happens with diesel injectors. 

If the threads were tapered like you suggest the soot would be right up to the threads around the side of the glowplug and would never come out again after a few thousand miles. 

[J.R.]

Aha, so its not the threads that are seizing but the highly compressed and carbonized soot occupying the clearance around the glowplug shaft behind the seal and the cylinder head bore up to the threads!

 

Now I can see why you are going to be very lucky to extract a seized one.

 

Is there  anything that can be done to minimise the risk of a newly fitted glowplug not sealing other than only replacing them when they have failed?

 

Is any carbon leakage visible in the first week or month or does it stop at the threads?

 

If none would removing and refitting after a month to see if there were any leakers do more harm than good, would the good plugs not reseal the second time?

[J.R.]

Its a shame they do not have a weep hole drilling so that any combustion escape would be visible and it could also be used for getting penetrating oil into where it was needed.

 

I expect the water jacket is in the way.

 

Not that the manufacturers would have any incentive in spending money to decrease their service revenue.

[ApertureS]

1 hour ago, J.R. said:

Aha, so its not the threads that are seizing but the highly compressed and carbonized soot occupying the clearance around the glowplug shaft behind the seal and the cylinder head bore up to the threads!

 

Now I can see why you are going to be very lucky to extract a seized one.

 

Is there  anything that can be done to minimise the risk of a newly fitted glowplug not sealing other than only replacing them when they have failed?

 

Is any carbon leakage visible in the first week or month or does it stop at the threads?

 

If none would removing and refitting after a month to see if there were any leakers do more harm than good, would the good plugs not reseal the second time?

Carbon leakage stops at the threads and doesnt often get past. You can refit glow plugs but you still have to go through the steps below again. 

 

There are 3 things that arent just 'helpful' but ESSENTIAL - yet hardly any garage or person ever does them and this is why the poor sod then has to deal with this situation.

 

1. TORQUE THE GLOWPLUGS CORRECTLY - Everyone tightens them down and goes 'oh just a bit more', glowplugs dont often go above 5-10Nm which to most is basically loose so people 'nip them up' with a ratchet probably putting up to 25nm of torque on them, thats a hell of a lot more.

2. Use a ceramic grease (not lithium or moly) on the shaft, a tiny amount - this just means if they do have a blowby then it doesnt stick nearly as much

3. Before fitting the new ones make sure to use a hole reamer as pictured below. This will first clean all deposits off the tips entry point and then use a very long thin wire brush to clean the mating face up. A quick squirt of brake cleaner to make sure the face is perfectly clean and fit the new plug.

 

[J.R.]

Thanks, that is great info.

 

I confess I would have almost certainly made the overtightening mistake on the one and only set that I fitted.

 

As mine are still (I hope) the factory fitted ones then I will not be changing them proactively unless equipped with the tools you recommend, and it does sound like a removal and refitting after a month might be a good precaution although if one is leaking unless the plug tapered face is damaged (unlikely) there is not a lot could be done other than the 'oh just a bit more' I suppose if you have one leaker then you could remove and clean it and the bore annually.

[SuperbTWM]

I think these reamers have been brought up before on this forum, not sure how I feel about breaking loads of carbon off inside the cylinders though.

 

What has always baffled me is how short the glow time is on modern diesels but I have recently learned that aparently it takes just 2 seconds to reach 1000C 

[ApertureS]

2 minutes ago, SuperbTWM said:

I think these reamers have been brought up before on this forum, not sure how I feel about breaking loads of carbon off inside the cylinders though.

 

What has always baffled me is how short the glow time is on modern diesels but I have recently learned that aparently it takes just 2 seconds to reach 1000C 

Ive dropped much bigger chunks of carbon into a cylinder before and started it up, bit of a noise then nothing. No problems - not that i recommend it!

 

Also with new glowplugs which are ceramic they get to 1000 degrees very quickly and rather than use a 12v switched relay they work on PWM voltages from very low voltage high current. This means they can regulate their temperature very closely. 

It also means you DONT test them with a 12v supply, youll damage them, do a resistance check and that is all. 

[SuperbTWM]

5 minutes ago, ApertureS said:

Ive dropped much bigger chunks of carbon into a cylinder before and started it up, bit of a noise then nothing. No problems - not that i recommend it!

 

Also with new glowplugs which are ceramic they get to 1000 degrees very quickly and rather than use a 12v switched relay they work on PWM voltages from very low voltage high current. This means they can regulate their temperature very closely. 

It also means you DONT test them with a 12v supply, youll damage them, do a resistance check and that is all. 

 

Max voltage for pre start glow is effectively11.5V according to the manual but would you really want to try and power up something on the bench thats going to get to 1000 degrees in 2 seconds, I know I wouldn't

 

Post glow down to 4.4V max 

[J.R.]

Regarding the carbon swarf those of us old enough to recall regularly decoking (I used to do several a week) or rebuilding engines will know from the formation of carbon on the piston crowns that flakes of carbon are constantly detaching and passing through the exhaust as the thickness builds up, you can see them ejected glowing red hot from a straight through exhaust system on dyno runs.

 

Even aluminium swarf that evades removal when helicoiling spark plug threads does not do any noticeable damage.