One year old bad glow plug
 

I had the classic signs of a bad glow plug, no pre-glow light, rough starts. I ohmed out the connector leading to the plugs, and saw 2.6 MΩ on #3. With the cross pipe off, and #3 disconnected, I measured the plug directly and see 2.6 MΩ to ground. So definitely a bad plug. Luckily, I can reach it without taking the intake manifold off.

My question is, what's the chances of the plug breaking after being in the car just one year? Are they weak from the get go, or does it take time? The top end was rebuilt and clean as a whistle when the new plugs were installed; I don't know if that makes a difference. Also, should I try to take it out cold, or with the engine warmed up?

Thanks.

It's pretty rare to break a glow plug. If you're worried about it get the engine warm and spray some penetrating oil on the threads of the plug, then let is sit for a hour or more. Then try to take it out. If it's tight don't use hammer on the wrench to break it loose. They aren't supposed to be screwed in really tight but people tend to ever do it and/or they get tight from the heat.

Just do a search on "broken glow plugs", and you will find out that it is not a "rare" occasion. With that being said, I think you have an excellent chance of getting yours out without a problem. Buru recommends that you stay within the 45-50 N/M range when trying to loosen the plugs. Some forum members recommend warming up the engine, and using generous amounts of PB Blaster. When I did mine, 4 plugs came out just fine, but the other two took over 2 days of spraying and moving them back and forth 1/4 turn at a time before the were able to be removed. I believe that the major problem is that the design of the plug allows them to become carbon bound, and prior to installation, the plug hole should be reamed with the appropriate tool. Good luck....

I dont understand why the system won't glow at all if there's one open plug. Seems to me that starting on 5 plugs is a lot better for the engine than starting on none.

I can't say for sure cause I don't know too much about your model, but in the earlier diesels, the GPs are still on with on bad one, it's just that the light doesn't come on to tell you that you have a problem. And depending on your compression it may be quite hard to start with one GP burned out. In my 123 wagon it was quite difficult to start with one GP out. And it will idle rough for the first bit cause the cylinder with the dead GP is much colder and not running well at first until it warms up.

The system still operates with a burned out glow plug. Just because the light doesn't come on doesn't mean the relay isn't cycling.

broken or burned out?
 

Are you saying that the plug is burnt out or that it is mechanicaly broken somehow. Entirely different problems. Glowplug life is guite variable sometimes short as weeks or months sometimes years and years. Cheers Dan

Glow plugs are like light bulbs. They either work or they don't, and there's no set mileage or age when they go bad.

If this plug is only 1 yo, I assume it was installed with Never Seize on the threads so it should come out easily.

Regardless... warm engine, lots of PB blaster, remove with a torque wrench, never exceeding 50Nm. If it won't budge at 50Nm, respray with PB Blaster, go inside and have a beverage, try again in an hour.

I think OP needs to answer this question before we get any farther. It sounds burned out to me, others have assumed it is physically broken. Both are entirely possible.

Sorry for the confusion. It's burnt out. I decided to just take it to my mechanic that did the top end job last year. He told me that he used anti-sieze when he put them in. Thanks for the info everyone.

I dont speeek nm.

50 nm = ~37ft lbs.

http://www.thetoolhut.com/Torque-Conversion-English-Metric.html

This isn't totally true. As GPs get old the resistance starts to increase and you get a less than optimal heat from the plug. They do burn out like light bulbs but they don't necessarily burn at the optimum for their whole life. If you bench test and old GP you'll often find that it burns bright red to bright orange. A new one will be extremely bright orange to almost white. New ones will often leave sunspots in your eyes, whereas the older ones won't. Don't touch them though, they're HOT, obviously, something like 1600F.

The Glow Plug in the far left pic is not a good one because it is getting hottest at the wrong place on Element. That no good plug may actually Ohm OK.
The other pic on the right is a good Glow Plug getting hottest at the tip of the element. The tip is the part that extends into the Precombustion Chamber.

I figured my statement would trigger this response, but I still stand by it. Perhaps heat areas do not stay optimum throughout the life of the GP, but 99% of GP-related questions on the forum are a go/no go issue. If you're reading megohms, your GP is bad, if you're reading an ohm, there's 144 amps going through that plug on a 12v system. Ohm's law holds...If there's 144 amps going through your GP, it's turning into heat. No other option.

This is the best piece of advice on GP's in the thread.

I agree.

Do you think he lit his cigarette with the GP when he was done?:beatnik2:http://planetsmilies.net/smoking-smiley-5436.gif

I appreciate the instruction, Diesel 911. Thanks!

The Fuse is 80 amps. I would expect the Fuse to burn long before it reaches 144 amps.

Also the Glow Plug in my picture that is heating mainly in the middle could case a miss on that particular Cylinder because the Heat would be trying to heat up the Cylinder Head and the Coolant (because that is what surrounds the Glow Plug in that area of the Plug) instead of heating the Air in the Prechamber.
Even though the Glow Plug has only partially failed it may functionally mimic a dead Glow Plug.

No, I did not light a Cigarette with it.
I smoked a Pipe back in the early 1970s for 2 years (Tobacco only) after which I lost interest in smoking.
But, like past President Clinton "I did not inhale".:D

Answer
 

Best guess the glow plug should still come out fairly easy.

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NOTE:
Some of our customers that where forced to remove the head due to stuck/broken glow plugs, remove them every year to ream the hole, clean and lubricate the threads.
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While diagnosing the glow plug system, do NOT touch any part of a hot glow plug.

Glow plugs run 1000° - 1300°C = "2372° Fahrenheit" optimal temperature range.

Touching the glow plug wire nut can cause severe burns, especially if there is a fault causing it to overheat.

Trying to OHM a heating element designed for high temperature operation at ambient temperature gives a deceptive reading.

A new glow plug reads 0.7 OHM.

Heating the air to a minimum starting temperature of 850°C is critical for diesel engine start-up.

FYI:
The most common (good quality) "NEW" glow plug failure is over torquing the 8 MM wire nut = damaging the electrode internally.
This is an ELECTRICAL connection = watch the wire, and STOP tightening when it begins to move.

All of this being said, I junk any glow plug reading 0.9 or higher.
For best reading:
* Disconnect the glow plug harness from the relay.
* Red OHM meter wire goes on the 8 MM wire nut threaded pole/terminal.
* Black OHM meter wire goes on the steel body of the glow plug.

All of my used glow plugs are tested:
# With the HOT electrode in the jaws of a vice.
# Battery/charger ground attached to the vice.
# Positive applied to the wire nut threaded pole/terminal for 15 seconds.
After you have tested one good glow plug, and personally seen how bright/hot it gets, there is no mistaking weak/bad ones.


Please read the data in the following thread for further data.


Glow plugs link thread All diesel models
http://www.peachparts.com/shopforum/diesel-discussion/137732-glow-plugs-link-thread-post1019018.html



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It was a math exercise. If the fuse is 80a, then the resistance of the glow plug has to be more than 2.178 ohms (if the battery is at 13.2v) to not blow the fuse. I'm not makin' this stuff up...Ohm's law holds everywhere.

Huh???

Do you have a weak battery in your calculator perhaps because those numbers are way off! :confused:

The glow plug on the right is either not powered up long enough or is not getting full current. I have never tested a glow plug with just the tip glowing. Unless all the glow plugs I have tested were no good?

Pictures.

Never Touch Hot Diesel Glow Plugs!!!
http://www.peachparts.com/shopforum/diesel-discussion/134359-never-touch-hot-diesel-glow-plugs-post986836.html

NOTE:
I always keep one "NEW" glow plug in my tool box for demonstration/comparison testing.

Glow plug on the right been powered for 2 seconds. By 20 seconds the entire shaft (up to the bevel seal) should be glowing.

http://www.peachparts.com/shopforum/attachments/diesel-discussion/28981d1129501651-never-touch-hot-diesel-glow-plugs-a1.jpg

http://www.peachparts.com/shopforum/...1&d=1129501651

Yup, sorry bout that...I had watts on the brain when I typed amps. The concept is still there...resistance determines the amps, amps determine the heat generated.

It is a Monark not a Bosch glow Plug. And, it might be that I took the pic too soon. However, the point is that Heat strated at the tip and got hottest their first.

When I tested some Glow Plugs one at time with an Amp Meter the Meter pegged out and as the Glow Plug heated up the Amps dropped to around 16 amps and stayed there.
It only took about 2 seconds for the Amps to drop to 16 amps.

What is the best type of GP to use? I installed 3 new Bosch and it starts worse. I am going to put the old GP's in. I think they are Beru?

Most people use Bosch. Beru cost more, harder to find and may be slightly better.

However, this is the Bosch Glow Plugs made in Germany or France. It is possible that the are also made somewhere else now.

If you removed the Fuel Injection Hard Lines you may need to bleed the Air out of them by leaving the Hard Line Nuts Loose at the Injector and cranking until Fuel comes out. Afterwhich tighten them and attempt to start.

Answer
 

Bosch or Beru others burn out to fast.




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Recycled
 

for new members

I am changing the glows in the 85 300SD today. I got them all out with just the normal amount of grunting and cussing and they all look brand new.

So I decided to test them with the jumper cable and battery and they all look to be working just like new.

Now I am wondering if I have a bad wire on one of them.

I guess I will put the new ones in and hope for the best.

Any suggestions from the collective wisdom?

what I am now understanding about glow plugs, that even if they light up. They may not be good. They aren't like a light bulb, but more like a resistor. With age and voltage their values drift thus not producing the correct heat. So the only way to test them, is to ohm test them...if the reading isn't to that of a new one...its worn...also I've read that the glow plug relay produces 8-10v mine produces 10v....your battery produces 12-14v thus making the plug brighter and producing more heat....this is why people tell you to run a jumper cable to the plugs to see if that will start the car more voltage equals more heat..

The wires can be tested from the larger of the plugs in your gp relay. Pop it off and there are the termination points for each gp clearly marked on the connector.

To ground, each of them should read less than one ohm. Best scale to read them on is your lowest one.

Well, thanks Jay.

I have them all in and wired now. I am pretty warm now so I'll go out and reinstall the hard lines and see if it fires without too much stumbling.

that's a fast way to test them. BUT I must still emphasizes that you look at the glow plugs as a resistor....if you test them through the wiring harness...all that wire adds resistance....you have to remove them from the circuit to get a proper reading....

I got it all back together now but have not been able to get the air out of the lines and now the battery is down so I am waiting for it to charge for another go later. Unfortunately now its dark but should be able to getrdone by flashlight.

Thanks for all the help.

I don't have an ohmmeter though so perhaps I should break down and buy one.;)

A new glow plug reads 0.7 OHM.
 

I just bought 5 new Bosch. I have a pretty accurate Fluke. Just out of curiosity I measured the new and the old. 4 new were .8 and one was 1.2

The old ones were .4, .8, .6, .8, .2

So can we assume that the .2 one was the bad one or does resistance rise
as the fail, unless the element does burn out like a light bulb resulting in zero
resistance?

I just replaced ALL of mine beause I forgot about testing with a battery, although now I see that just glowing isn't all it needs to do, it needs to glow
in the proper way as well.

Actually the resistance of the copper wire is very close to zero. 3' of 10 gauge wire is .003Ω I doubt if most regular digital VOM's will read finer than .1Ω.

If you are pretty sure you have one out. Just pulling the connector at the harness will get you pretty close.

The box on my new Bosch plug had a pretty good representation of what is going on in the the pencil glow plug. There is a small coil of wire that travels down to the end of the probe. I can imagine it shorting on the inside of the pencil .

Well, after a couple of hours charging the battery it started right up with some wd40 to prime it.

I'd still like to test the old glows though so I guess I will buy an ohmmeter.

The GP resistance is very high/open circuit when it fails. Not zero. GP in general measures at very low resistance, < 2 ohm, are good. I reckon all the old one your replaced are good. When GP glows, the resistance will kind of reaching a steady state and draws about 10 to 12A. Most GP are rated at 120-150W ( battery voltage x current drawn, 12v x 12A = 144W ).

Tom, you can get a good meter at harbor freight for less than $20

We don't have one here. How about Autozoo?

A DT-830 is a cheep sturdy DVM that more than meets the needs we have to work on MB and Studebakers.

We need DC volts to 20
We need ohms to about 1000
We need a milli volt AC scale if we are working on a funky alternator issue.

A search in any auction site for " digital multimeter " will come up what what you are looking for. Currently on ebay over 9000 listings came up.

Answer
 

FYI:

Trying to OHM a heating element designed for high temperature operation (1000° - 1300°C = "2372° Fahrenheit") at ambient temperature gives a deceptive (FALSE) reading.

A new glow plug reads 0.7 OHM.
A BAD glow plug can depending upon failure read 0.7 OHM, or anything from open circuit to dead short.
I have many used glow plugs, for show and tell + hands on test at tech sessions.

IMO relying on an OHM test is playing Russian Roulette with a loaded Glock.

All of my used glow plugs are tested:
# With the HOT electrode in the jaws of a vice.
# Battery/charger ground attached to the vice.
# Positive applied to the wire nut threaded pole/terminal for 15 seconds.
After you have tested one good glow plug, and personally seen how bright/hot it gets, there is no mistaking weak/bad ones.


Please read the data in the following thread for further data.

Glow plugs link thread All diesel models
http://www.peachparts.com/shopforum/diesel-discussion/137732-glow-plugs-link-thread.html#post1019018


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No disagreement on bench testing being the best, but depending on the vehicle it can be a lot of work to remove the glow plugs.

I assume a professional like yourself working on a customer's car would normally replace all GP's for a preheating problem. An individual may want to only replace the defective GP.

Is there an installed GP testing method you believe to be reasonably accurate?

Based on the bench test methodology I believe the old plugs are all good. I will try again and use the time period you describe.

Removal of the plug to check heating pattern is the defacto standard.

However, it's a lot of work and isn't warranted unless you demand absolute performance in temperatures that are frequently below 0°F.

I've used the method with the ohmmeter for the last 12 years and have never failed to identify a bad plug. If the resistance is between .7 and 1 ohm, I let it go. If it's open or greater, I change it.

Fortunately, I have never encountered a plug that wouldn't perform but had proper resistance readings.