glow plugs failure

[gonzalo Senior Member Find all posts View Profile Close gonzalo]

Hello,


With the arrival of winter temperatures the car has been struggling to start in the morning. When it does it releases a ton of white smoke. After that it goes perfect.
The glow plug indicator in the instrument panel has been dead for a few weeks too.
This is quite strange because I fitted a new set of Bosch plugs exactly one year ago.

On Saturday I lifted the bonnet and checked for continuity between the plugs positive and the battery negative. In all of them the resistance was infinite i.e. open circuit.
Just to be sure I checked the current draw with ignition on and it was zero in all the plugs.
Voltage out of the relay was 12.6V on each pin, so the battery seems to be in good shape and the relay itself is ok too.

So I got the plugs out, fitted new ones and the car started within one crankshaft revolution. If it wasn´t for those moments….


I have attached a few images of the old plugs (ref 0 250 201 039).







Haynes owner manual states that if a glow plug fails and the probe is eroded or charred the typical cause is a defective injector. I am not sure how an eroded or charred plug to the point of failure looks like. If this is the case I believe WVO may have to something to do with it. I am thinking that perhaps carbon deposits at the injectors tips are causing them to spray poorly, which in turn causes the glow plugs to fail (the plugs are right in the “line of fire”). Something similar to over fuelling, I guess.

I have read some threads about Mitsubishis destroying glow plugs, but none about a Mercedes doing that.


So my 3 questions would be:

Do you think the glow plugs shown in the photos are eroded or charred?
What are those little balls in the last photo?
How long does a set of plugs last in your MB?



Thanks in advance
gonzalo

[froggo Senior Member Find all posts View Profile Close froggo]

Re: glow plugs failure

Hi gonzalo,

those glowplugs look deformed and overheated possibly due to overfueling and/or poor spray from injectors.

The middle two look like the outer shell may be breached(a hole) and full of carbon, this can give a continuity reading but the plugs don't heat up correctly. It also explains the dash indicator reading, the plug allows continuity but does not get the correct reading at the guage.

White smoke is also a sign the plugs are not heating up.

I would get your injectors cleaned, pop tested as you will just keep destroying glowplugs or cause worse damage.

I don't know if it is worth trying to clean your injectors with a fuel adative or with ATF first.

God bless froggo.

[gonzalo Senior Member Find all posts View Profile Close gonzalo]

Re: glow plugs failure

Hi gonzalo,

those glowplugs look deformed and overheated possibly due to overfueling and/or poor spray from injectors.

The middle two look like the outer shell may be breached(a hole) and full of carbon, this can give a continuity reading but the plugs don't heat up correctly. It also explains the dash indicator reading, the plug allows continuity but does not get the correct reading at the guage.

White smoke is also a sign the plugs are not heating up.

I would get your injectors cleaned, pop tested as you will just keep destroying glowplugs or cause worse damage.

I don't know if it is worth trying to clean your injectors with a fuel adative or with ATF first.

God bless froggo.

Thanks froggo. I too believe I need to clean the injectors. Will try AFT first and then, in the new year, will finally fit a WI system. I should have done this a while ago, but these have been busy days.

I take I should mix the ATF with the diesel in the auxiliary tank. Would you recommend a particular mix ratio?

Other than the carbon deposits the injectors should be ok because I fitted new nozzles a few months ago and had them pop tested.

Cheers
gonzalo

[froggo Senior Member Find all posts View Profile Close froggo]

Re: glow plugs failure

Hi gonzalo,

I think it's Alga who knows more about ATF for cleaning injectors. Do a search on it, there is info about how to do it.

There is another way that overfueling occurs and it's due to the ip. Once you have given the injectors a clean if the problem is still there that would be the next place I would look.

God bless, froggo.

[Westwinds Donating Member Find all posts View Profile Close Westwinds]

Re: glow plugs failure

Gday Gonzalo,We know how the veg oil collecting business is going in Oz.I am wondering how is it in Spain.Regards Westwinds.

[gonzalo Senior Member Find all posts View Profile Close gonzalo]

Re: glow plugs failure

Hi Froggo, I have cleaned the old plugs and one of them is showing erosion that has gone all the way through the probe, like you were suspecting. The other 3 are not that bad.





I will read Alga messages for the ATF ratio.


Westwinds, you may find some info about WVO collection in Spain in a thread titled "oil glut". It is becoming quite difficult, really. Only 5 years ago I would have had as much more oil as I wanted, but legislation has changed since to control WVO as if it was liquid gold.

Regards
gonzalo

[froggo Senior Member Find all posts View Profile Close froggo]

Re: glow plugs failure

Hi gonzalo,

yes, that looks like the one causing the problems. Same thing happened to one of mine, showing the same symptoms you were describing.

God bless, froggo.

[tbird650 Senior Member Find all posts View Profile Close tbird650]

Re: glow plugs failure

I've had this exact kind of glow plug failure too. I used to buy them by the box of 10. A box lot would last a year. That got to be a bit expensive. At the time my injectors were carbonizing too, requiring cleaning every 3 or 4 weeks.
My fix was to blend and it has completely cured both these problems. I should mention I also fitted a switch to interupt the glow plug trigger circuit. It uses a simple push button.
My current blend I use without heat exchanger/s. 80veg-10ulp-10dino. Varies with time of year. The blend gives reasonable power & good starting.

[gonzalo Senior Member Find all posts View Profile Close gonzalo]

Re: glow plugs failure

ok, so it looks like the problem maybe carbon deposits at the injectors.
I would like to avoid blending, so will fit the WI system and see how it goes.

Thanks for your replies.
gonzalo

[tbird650 Senior Member Find all posts View Profile Close tbird650]

Re: glow plugs failure

ok, so it looks like the problem maybe carbon deposits at the injectors.
I would like to avoid blending, so will fit the WI system and see how it goes.
gonzalo

Well, I thought the problem was to do with high speed Jap diesels. I'm surprised to see a Merc suffer the same fate. I had the theory that as the injectors carbon up more and more, the glow plugs got showered with heavier and heavier deposits.
I also have to wonder just how much ambient temperatures make to the equation. Certainly it makes a difference how much blend percent I can get away with. Obviously with money I'm saving on GP's, I can afford some blending!
I watch with great interest the WI outcome.