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.