Spark Plug Replacement: Risk of Breaking

Hello everyone,

What is your opinion/experience regarding the likelihood of spark plugs breaking when being unscrewed from a 14-year-old engine with approximately 200,000 km (the first set of spark plugs are still installed)?

This winter, the car has been starting so poorly that I was thinking of replacing the spark plugs. However, I'm a bit apprehensive after reading about how often this procedure goes wrong.

Are there any tips you can offer? Letting a generous amount of WD40 soak for a while probably can't hurt, but what about the tip to "warm up the engine"? Does the engine need to be cold when installing the new spark plugs? At least, that's what I remember from my days with gasoline engines, where spark plugs were never supposed to be screwed into a warm engine.

Thank you!

First, check what the candles indicate regarding the resistance measurement.

Attention, my DB expert friend pointed out that in the CDi, the GK (presumably referring to a specific component) gets extremely hot very quickly due to slight tearing.
The R measurement is not always reliable due to the afterglow or persistent illumination of the filament.
Using the power consumption as a reference point is a more reliable approach.
You can install new, cold glow plugs into a hot engine, but don't tighten them immediately.
Wait until they have absorbed the temperature. And don't forget the special fat!

Use a small torque wrench. The breakaway torque for an M10 spark plug is approximately 35 Nm.

Hello,

The most important thing, as mentioned before, is to ensure the engine is properly warmed up beforehand. Initially, try to loosen the spark plug with a quick, forceful movement (torque slightly higher than the breakaway torque). Then, carefully unscrew it a little (1-2 turns) and screw it back in. If it seems relatively easy to turn, warm the engine up again and then fully unscrew the spark plug. Apply penetrating oil throughout the process.

Best regards,
Albrecht.

Okay, it seems that running the engine hot is common practice for breaking in new spark plugs, but should you also install them when the engine is already hot? I'm still not quite sure about that, for historical reasons I mentioned earlier.

But the real question is: What are your experiences ("statistics")? Have you ever (or rarely) experienced any major issues using the described methods?

So far, I've only had experience changing glow plugs on a W202 220CDI. Even then, I only did it when the engine was slightly warm because the car is so tightly packed. I would loosen them abruptly, turn them out a few rotations, and then screw them back in. And so on, until they were all out. I haven't had any problems with it.

Of course, letting the dough rise slowly is better, but who has time to wait?
Therefore, my suggestion is to tighten all the screws properly and make sure they are securely fastened after the waiting period.

kossmann wrote:

After the methods described - have you ever (relatively rarely) experienced any issues?

You often hear reports of stripped spark plugs, especially from Mercedes-Benz owners.

kossmann wrote:

But the real question was: What are your experiences ("statistics")? Have you ever (relatively rarely) experienced any major issues

after using the described methods?

So far, only one Champion spark plug has come loose on the Audi 75, and I must emphasize that it was during removal!
But I haven't replaced even 50 sentence GK yet.

Nowadays, there are also some great tools available. For people who do this kind of work frequently, I saw a small impact wrench from KS Tools that uses vibrations to loosen the seized spark plugs. It's specifically designed for this purpose.
And then there are various (expensive) tools for repairing it if it happens. However, the tool catalogs almost always list "CDI" for these tools.

Here is the vibrator, located in the top right corner: http://www.projektnet.nazwa.pl/karmet/promocje/LL07_20D_Motor-Spezial.pdf

To complete the thread:

I just replaced the spark plugs... it was completely easy. The old spark plugs came out very smoothly, and the new ones went in without any problems .

A stroke of luck . Congratulations.
Did you apply any Beru spark plug grease or something similar to the threads of the new spark plugs?

No, I wanted to use copper paste first, but it didn't seem to be stuck to the old candles, so I left it alone.

Welcome to the new GK life.

"It will be fine, it's not a CDI."
If everything goes well, we'll be able to drive 200,000 kilometers before the next service.