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Seek to understand,^Value
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Discussion Starter · #1 · (Edited)
Why would Bosch spark plugs be prone to loosening & backing out & needing timeserts?

Why would Bosch spark plugs (reputedly) seem to be loosening up (causing them to eventually blow out of the engine, taking the threads with them) purportedly more so than NGK or BMW OEM spark plugs?

A thread today has yet another user faced with having to timesert the engine to repair damage from Bosch plugs that loosened and blew out, taking a few threads with them:
> E39 (1997 - 2003) > Stripped Spark Plug Hole.

Other threads have alluded to the same situation, where Bosch spark plugs loosened, causing knocking sounds and burned components, before, eventually, blowing out of the hole taking the last few threads with them.
> E39 (1997 - 2003) > Spark plug blown out of the head!!

While other threads cover what size timesert to use, and how to use them:
- Time-sert

This thread specifically asks if we have any engineering data on WHY the Bosch spark plugs might be more prone to backing out than, say, the original BMW or NGK replacement spark plugs?
 

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Seek to understand,^Value
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Discussion Starter · #2 ·
Running a search, I haven't found a logical answer yet - but I did find anecdotal evidence, as shown over here...
> E39 (1997 - 2003) > Spark plug blown out of the head!!
I am unsure of why this happens a lot with Bosch plugs.

Running an E46 and E39 only title only query for "Bosch" plugs "backing" out, netted so few threads that I widened the search to posts, which anecdotally refer to the Bosch plugs backing out, but, not WHY they back out.

> E39 (1997 - 2003) > My E39 just deciede to start knocking !!
> E46 (1999 - 2006) > Spark plug/coil boot replacement
> E39 (1997 - 2003) > Spark plugs!!!
> E39 (1997 - 2003) > Loose spark plugs
> E39 (1997 - 2003) > Loud knocking when idling
> E39 (1997 - 2003) > Spak plugs for 540I
Given we have sporadic posts about Bosch spark plugs backing out, I think we need a thread which attempts to explain WHY this might be happening.
 

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Discussion Starter · #3 · (Edited)
If this theory below holds true, then the Bosch spark plug length would likely be slightly longer than the NGK or OEM BMW.

Is that the case?
- One cause of stripped spark plug threads?
Is it possible that the plug threads extend a few mm beyond their aluminum female bmw partner's parts into the combustion chamber?

My theory is that the extended couple of mm of threaded section might accumulate carbon and corrosion, corrosion that is sturdy enough to deform the aluminum on the way out, but once dragged all the way through appears to the eye to be quite corrosion free? Force this corrosion through the aluminum a few times over the years and, voila.... your baby's aluminum female parts are just whored completely out of whack and no longer capable of holding the male parts home. And tragedy.... why of course!

I mean, I anti sieze and everything. Even use a torque wrench to spec it. Even back off a bit from spec out of fear. I'm pretty conciencious. But anti sieze would burn off of any exposed threads in short order. Is the theory just my imagination?
 

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BMW does not recommend the use of anti-seize for spark plugs. The torque spec is for dry threads. Most modern plugs have a plating on the threads that minimize seizing. I never use it on my car, and have had no problems removing plugs.

AFAIK, the Bosch Plus 4 is the only one that loosens up.
 

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Running a search, I haven't found a logical answer yet - but I did find anecdotal evidence, as shown over here...
> E39 (1997 - 2003) > Spark plug blown out of the head!!

Given we have sporadic posts about Bosch spark plugs backing out, I think we need a thread which attempts to explain WHY this might be happening.
We need much more evidence...the most important is whether these spark plugs were installed correctly in the first place. Meaning were they properly threaded (not cross threaded) and tightened to factory specification with a calibrated torque wrench? I have never had a spark plug back out of any car...and for years, I never used a torque wrench...but 7 years ago I started using a torque wrench, after reading some of these threads (might have even been one of yours Bluebee ;) )

I installed some plugs in my car by my usual method by hand. Then used my calibrated torque wrench to see how close I was to spec. I was WAY TOO LOOSE! I believe I turned the plugs about 3/4 turn more to reach proper torque. So don't trust your arm...get a torque wrench (preferably a good quality one) , take good care of it, and get the wrench periodically checked for proper calibration.

Bentley workshop manual states spark plug tightening torque should be 25NM or 18 ft/lb (says use anti-seize)
NGK website say torque should be (recommends using torque wrench) 25 to 30 NM or 18 to 22 ft/lb (says no anti-seize)
Bosch website says torque should be (recommends using torque wrench) 26 to 30NM or 19 to 22 ft/lb (says if using anti-seize, reduce torque by 30%)
 

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BMW does not recommend the use of anti-seize for spark plugs. The torque spec is for dry threads. Most modern plugs have a plating on the threads that minimize seizing. I never use it on my car, and have had no problems removing plugs.

AFAIK, the Bosch Plus 4 is the only one that loosens up.
Actually, the Bentley states to use anti-seize (copper based), but you are right, conventional wisdom is not to use anti-seize, and most spark plug manufacturers will tell you it is unnecessary, as they use plating and threading that does not require it.

I have seen threads for both Bosch and NGK coming loose. I think it was Bosch that we have had reports of occasionally losing one or more of the four prongs (there was a rash of them about 8 to 10 years ago). But I have not seen any issues in the past 5 years or so (perhaps Bosch had a quality control issue?). I installed Bosch Fusion +4 (iridium) plugs in my car a few years ago (this is supposedly an improved version of the still available Bosch +4 platinum plug)...been almost 70k miles, no issues. Took a couple out to inspect recently, they looked almost new....like they had been in the car for less than 10k miles.
 

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How weird that this kinda pre-supposes that such a plug even exists that is prone to "backing-out"??!! I have used Bosch rather religiously since a young guy once I became familiar with the company (I'm 60 now so been a long while) and have never had an issue with any of their plugs in both steel, domestic heads and foreign aluminum heads (Nissan, BMW, Audi). Never a back-out and can't even remember changing one EVER for a mis-fire. They just keep-on, keepin'-on for me. I guess YMMV.

I would think more a situation of installation method. When I use anti-seize which is very often, I always go back after a week or so and re-torque. For some reason, they seem to become sort of "relaxed" when used with A-S and can after a few heat cycles need a tweak. Just my personal exp.
 

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In my E39 with NGK Iridium and antiseize, zero problems, no plugs working loose.

However, plugs working loose is seen in many cars, not just BMW. In the Honda Odyssey van forum, there are plugs that fly out of cylinder #3 and punched through the underside of the hood. Why only #3 cylinder in Honda Odyssey, I don't know!

There are different cause for spark plugs blowing out of head, just google and you will see:

1. Incorrect torque ---> plugs working loose over time.

2. Bad cylinder head threads ---> plugs are correctly torqued but the aluminum threads on the head simply break off (Ford engines!) ---> plugs and cylinder head threads flying out...
 

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Discussion Starter · #10 ·
AFAIK, the Bosch Plus 4 is the only one that loosens up.
This is a good start, since, we can start asking the NEXT person if their backed-out plug was a Bosch Plus 4.

Also, we can start comparing that specific Bosch Plus 4 to the NGK/BMW plugs to see if anything meaningful is different.
Surrounding the center electrode, which contains 75% more platinum than previous Bosch platinum plugs, are four "surface air gap" ground electrodes made of a special wear-resistant nickel yttrium alloy. The angle and position of the four electrodes creates multiple spark paths that cause the spark to jump sideways. This has a self-cleaning effect on the center electrode and results in a longer, more powerful spark that reduces misfires for improved engine performance, better fuel economy, lower emissions and faster acceleration.
When these spark plugs fire, the spark jumps randomly to any one of the four ground electrodes. It does not jump to all four electrodes at the same time. This spreads the wear across four electrode surfaces instead of one as is the case with a standard single ground electrode spark plug.
Bosch says their tests have shown the new Platinum +4 plugs can improve fuel economy up to 4.8% over other competitive spark plugs. Fouling resistance is also said to be 33% better.
Though Bosch makes no specific mileage claims for their Platinum +4 spark plugs, they do say the plugs meet or exceed OEM requirements for 100,000 mile replacement intervals. Bosch says the plugs show almost no increase in firing voltage requirements after 100,000 miles of operation. Bosch has also run tests where the plugs have gone over 150,000 miles with no appreciable wear, so these would seem to be lifetime plugs for many vehicle applications (unless, of course, the engine is burning oil, in which case fouling might occur).
Another unique feature of the Platinum +4 is that the surface air gap between the center and four ground electrodes is factory present to 1.6 mm and is nonadjustable. No attempt should be made to adjust or change the air gap when the plugs are installed, even if the air gap specification is different from that specified for a standard spark plug. The wider gap of the Platinum +4 is necessary to achieve the advantages above.

 

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Seek to understand,^Value
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Discussion Starter · #11 · (Edited)
We need much more evidence...the most important is whether these spark plugs were installed correctly in the first place.
Who can disagree with that? If I had a plug back out, my FIRST assumption would be that it was put in wrong.

I should confess, in my failed search for WHY the plugs reputedly backed out, there were probably as many posts where people said they had been using Bosch plugs without problems for years (I didn't post those because I was specifically looking for failure situations).

We should probably start asking owners how their plugs are faring.
Here, for example, is a BMW E39 98 528 that replaced NGK with Bosch plugs way back in 2008:
> E39 (1997 - 2003) > Spark Plug DIY for E39 98 528

As Edjack said above, it could still be that only the Bosch Platinum Plus4 plugs are "prone" to backing out, which would mean:
1. Most Bosch plugs would be fine, and,
2. Not all Bosch Platinum Plus 4 plugs would back out anyway.

I do agree fully that we need more evidence (either way).

EDIT: Here is a description of the Bosch plug where it is noted that the plating is silver, not platinum (if that matters).
> E39 (1997 - 2003) > Pictorial DIY for an M54 spark plug replacement on a 2002 BMW 525i E39 with 95K miles
While this is a Bosch document (and most of us use NGK plugs), I found there is a lot of potentially useful technical information in this brochure I found while researching how spark plugs work:
- Bosch_BMW_official_spark_plug_guide.pdf

It's interesting that the center electrode is not platinum plated ... it's silver plated!
 

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Discussion Starter · #12 · (Edited)
How weird that this kinda pre-supposes that such a plug even exists that is prone to "backing-out"??!!
Just to be clear, I'm fine with whatever the truth turns out to be.

Certainly some people have assumed that the Bosch (insert-model-here) plugs back out more so than others - but - as already noted ...
1. Many people have no problem with Bosch plugs, and,
2. Most problems must be due to installation error (right?), and,
3. Even NGK/BMW plugs have problems (as cn90 noted).

All I'm trying to do is figure out two things:
a. Do Bosch (insert-model-here) plugs back out more than NGK/BMW or not?
b. If so, why

Here are some anecdotal snippets I've found by running a quick search of this forum only ...
> E39 (1997 - 2003) > Spark plug blown out of the head!!
sparks plugs backing out of the head are a known problem with the bosch plugs. For that reason most of us use the ngk brand.
No one is really sure why only the bosch seem to do this.

This happened to my ford e-350 once. Not sure of the plug brand there but it blew my whole motor as the threads got sucked in.
sparks plugs backing out of the head are a known problem with the bosch plugs.
> E39 (1997 - 2003) > My E39 just deciede to start knocking !!
check the tightness of your spark plugs. especially, if you are running bosch, a plug that has loosened or backed out will tick & sound like a bad lifter
> E46 (1999 - 2006) > Spark plug/coil boot replacement
Some of you may have read my "3000 rpm hesitation" post. As part of my continued PM regimen I have replaced my spark plugs and coil boots. I had my spark plugs replaced when I bought the car about 3 years ago by the dealer. I was initially just going to change the boots but I had NGK plugs that I bought a year ago so swapped them as well. Pics below.

My initial thoughts are that the wear is "ok" to "good" which to me is unacceptable. The plugs were Bosch and were very loose. In other words, when loosening them there was very little to no "break" in the tightness. I was surprised to say the least considering Bluebee posted in a DIY (hand tight then 180-240 degrees). I will start off by saying all plug wells were dry, it was only plug 1 and 6 that had a bit of wet oil under the washer of the plug. This is my concern as that means oil is passing the rings or this may be due to how loose the plugs felt when removing them.
> E39 (1997 - 2003) > Spark plugs!!!
I personally use NGK and would recommend that you should definitely avoid Bosch. There have been several posts regarding Bosch spark plugs backing out of their holes. I thought this was a myth until it happened on my brother's e46. Whatever you choose, I doubt there will be any noticeable difference in performance. So go with what your gut says and torque them in place!
> E39 (1997 - 2003) > Loose spark plugs
Today I had some time so I thought of checking the car in preparation for VANOS . I had this loud ticking sound for some time and thought something was loose on the exhaust side, but never gave it much thought and car felt usual.

Today I removed the engine cover and sound became even louder. I recalled that a thread in bimmer forums was mentioning loose spark plugs. So thought of checking plugs , put my ear to on top of the engine and it felt as if the sound is coming from cylinder# 5. Removed the coil and yes it was 5th cylinder, The well was soaked in oil, tightened the spark plug and sound is gone.
However I did not tighten the plug more than 1/4 turn , it felt too tight, I will check back again in week or so. Spark plugs are Bosch platinum.
+1 on vcg repair. while your there change out the plugs to ngk & the coil boots if they are old. bosch for some reason or another has a known issue w/ backing out.
> E39 (1997 - 2003) > Loud knocking when idling
Check your spark plugs to make sure they are all snug. I had a loud knock/tick that drove me nuts. I found 2 spark plugs that were loose, tightened them up and it's nice and quiet since. This has been known to happen on these engines and many posts about this can be found (when I searched I was very suprised how many people fixed the ticking/knocking by finding a loose plug or two and then tightening them). Folks seem to say the OEM Bosch plugs are notorious for "backing out" and they recommend another brand (can't remember). I have fairly new Bosch plugs but I just check them every once in a while ever since I had this issue.
Good luck!
> E39 (1997 - 2003) > Spak plugs for 540I
DO NOT use Bosch Plus 4s!!! Ask me why.

The TIS lists Bosch F7LDCR and NGK BKR6EK up to 7/97; F8LDCR from 7/97; NGK BKR6EQUP for all M62TU. These part numbers may have been superseded, so make sure you get the correct ones.
Let me tell you about Bosch Plus 4 plugs (BTW, these were not platinum, but the platinum plugs appear to have the same wimpy ground electrodes):

This happened in '02. My 540i was missing badly at engine speeds below 2000 RPMs. I pulled all the Bosch Plus 4 plugs, and found that one had NO ELECTRODES, and another had only one! Both plugs were also finger-loose, and there had been blow-by through the threads.

It's very possible that I did not properly torque these plugs when I installed them, and they loosened up. However, others have had them loosen up, even with proper torquing.

Once loose, the plugs could not transfer heat to the head, and probably got hot enough to loosen the electrodes, or even vaporize them.

The plugs were in there for 10K miles.

I replaced them with Bosch F7LDCRs, which are copper-core, 2-electrode plugs, and are specified for this model year.
I put anti-seize on the plugs because I've never heard of anybody *not* putting anti-seize on a plug. Doesn't the V-8 have an aluminum block? That's likely to cause big corrosion issues with the plugs unless anti-seize is there, isn't it? I used anti-seize on the iridium plugs with no problems.

Also, why would this problem be isolated to Bosch Plus 4 plugs? It seems like any plug is just as likely to have problems backing out as any other.
> E39 (1997 - 2003) > Pictorial DIY for an M54 spark plug replacement on a 2002 BMW 525i E39 with 95K miles
picked up 6,bosch platinum +4's but after reading all I could, decided to return, lol. picking up ngk 3199 on way home.
I returned the Bosch's and got the NGK's. Glad I did.
> E39 (1997 - 2003) > Best spark plugs to use?
At the shop I work at we have actually had a lot of problems with Bosch plugs in any BMW. The only plugs we will use are NGK. Never a problem with them. Had problems with rough idle, low power, bad gas milage all fixed with NGK plugs and pulled out new Bosch. Just my experience with Bosch.
Like I said earlier. BMW discontinued the use of Bosch plugs.

Originally, the E39 came with either Bosch or NGK plugs. But a few years ago, BMW stopped using Bosch and sent a memo (forgot what they call that memo - service bulletin or something like that - I posted that somewhere in this board when I discussed this with Bluebee), in that bulletin they instructed their dealerships that the Bosch is no longer to be used, and the only plug to use now on ALL E39s is the NGK BKR6EQUP, even on cars that had something else from the factory (like the older NGK).

So your shop's experience with the Bosch plugs seem to be similar to BMW's.
one thing is dont buy the bosch platiums they will do more harm than good. just buy regular ngk or bosch.
Bosch is known to break up. i,e. the two prongs (or 4 prongs) breaking off the plug and falling into the cylinder. Specially with the thinner prongs making hot spots and causing pre-ignition or detonation the chances of that is higher (however it might be a myth. I've never tried it).
 

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Discussion Starter · #13 · (Edited)
There are different cause for spark plugs blowing out of head, just google and you will see
This Bosch backing out propensity discussion came up over here about five years ago, based on a search I just ran ...
> E39 (1997 - 2003) > did I just drop a cylinder? (Blown plug, please help)
Just as I suspected and likely not your fault then. Lots of folks have reported that the bosch plugs back out after being torqued down. Yours probably backed out a few threads and then the compression of the engine pushed it right out taking the threads with it.
I don't get it.

Why would a Bosch spark plug "back out" if tightened properly when an NGK wouldn't?
I don't know the exact answer Bluebee, but I have seen it reported at least a handful of times now if not more. Some catch it in time, others don't get so lucky and have problems such as what the OP is going through. I've got bosch plugs in one of my cars right now. I think I'll be picking up some NGKs at my earliest opportunity though.
You can add me to that list. I had Bosch Plugs in mine when this happened to me!
Either the suspect spark plug was:
- cross-threaded
- not tightened to proper torque ---> working its way loose ---> blow out.

Helicoil is OK but "Timersert" is better.
- Helicoil is basically a Spring
- Timesert is basically a Sleeve.

Practice this on a junk engine first! Or take it to a pro mechanic to install Timersert.
Metals expand and contract from heating and cooling at different rates. Substandard materials, testing, design can lead to plug loosening due to contraction and expansion. Normal engine vibration exacerbates problem until plug is finally loose enough to be blown out by the engine compression/fuel ignition.
 

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As I posted previously, my own "test" has found that what I thought was tight, was not, when installing spark plugs. I tightened them down, then used a torque wrench and it took another 3/4 turn to get them to the proper tightness. It is possible there is a difference in the washer used on Bosch, that gives a different "feel" as it "crushes" during final torqueing and this is throwing people off to thinking they are tight, when they are not.

All I can confirm, is anyone wishes to avoid this problem, then use a torque wrench that is properly calibrated and you can trust. That is the only way to consistently and assuredly meet the proper tightness.

Also be aware, torque wrenches can be wildly inaccurate, and it is worth having yours checked, and confirmed it is within spec. I have had both of mine certified by the manufacturer to +-3%. Wasn't expensive to have done, and you can even have the service performed locally if you search around. A friend had both of his new (two months old) Craftsman torque wrenches checked, both were out of calibration.
 

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Who can disagree with that? If I had a plug back out, my FIRST assumption would be that it was put in wrong.

I should confess, in my failed search for WHY the plugs reputedly backed out, there were probably as many posts where people said they had been using Bosch plugs without problems for years (I didn't post those because I was specifically looking for failure situations).

We should probably start asking owners how their plugs are faring.
Here, for example, is a BMW E39 98 528 that replaced NGK with Bosch plugs way back in 2008:
> E39 (1997 - 2003) > Spark Plug DIY for E39 98 528

As Edjack said above, it could still be that only the Bosch Platinum Plus4 plugs are "prone" to backing out, which would mean:
1. Most Bosch plugs would be fine, and,
2. Not all Bosch Platinum Plus 4 plugs would back out anyway.

I do agree fully that we need more evidence (either way).

EDIT: Here is a description of the Bosch plug where it is noted that the plating is silver, not platinum (if that matters).
> E39 (1997 - 2003) > Pictorial DIY for an M54 spark plug replacement on a 2002 BMW 525i E39 with 95K miles
It doesn't really matter....but more importantly the Super 4 is an older tech plug and I do not believe it is spec'd by Bosch for the E39 series. The OEM spec plug in the BMW manual recommends the Bosch Platinum +4. Bosch also recommends their newer, Bosch Platinum Ir Fusion plugs, which is similar to the Platinum +4, but adds an iridium/platinum center electrode tip. I have been using them for the past 70k miles or so with no issues...previously I have used a couple different sets of OEM NGKs, I have never noticed any difference amongst them all....
 

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Discussion Starter · #16 ·
> E39 (1997 - 2003) > Spark plug blown out of the head!!
How weird as this kinda pre-supposes that any plug has a propensity to back-out of the head over a different brand or type plug. I have been using ONLY Bosch plugs ever since first hearing of the company many, many years ago (I'm 60) and have used Bosch in steel domestic heads as well as foreign (Nissan, Audi, BMW) aluminum heads and never had this issue. That's over 35 years.

I would think it a matter more of install technique; just my opinion. I use anti-seize 100% whether the manual says so or not. I find (just personally) that when I use anti-seize I must torque and then go back after about a week of hot/cool cycles re-torque as for some probably logical reason that escapes me, they seem to relax a little probably BECAUSE of the A-S. I have never even had a Bosch mis-fire over time! In my exp. only (YMMV), they just keep-on, keepin'-on! I am sure it is a function too of ring conditions (oil-fouling, etc.) which I just have been fortunate enuf to not have- knock wood.
I'm betting the problem lies with improperly tightened spark plugs. I would even go so far as to suspect (just a guess) that Bosch may use a slightly different design washer that as it compresses/yields, gives the impression it is tight when it is not. Thus, if people simply used a torque wrench it would avoid the problem.
 

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Just a complete guess and others should feel free to add, but for one plug *brand* to be more prone to release under combustion can only (in my mind) be related to the actual thread or a feature that "fools* installers such as what 540 M-Sport theorizes. T he crush washer is softer, thicker, harder, who knows? Just gives false sense of tightness if a torque wrench is not used which is common I think.

The only other things I can see making one plug more prone, would be the material plug body (threads) are made of, the depth of the thread when cut (really a function of actual
O.D. of plug threads) or the thickness of the thread itself. Was it cut "thin" which can be the case and a thread can still be 1/2-12 or whatever, These dimensions are dictated however by the ASTM and others. I buy wholly into 540 M-sports theory and my own that for some reason, the plugs just aren't installed to fully the spec. Things about this Bosch may be different as he suggested such as how crush washer "feels" to those who opt to not use a torque wrench. I DO USE a torque wrench, but still find that I always need to come back after a few drives only to find the plugs will accept about a 1/4 turn before torque wrench "clicks". I have checked again a week later and never found any loosening after one "touch-up". I guess I attribute to A-S. Makes no sense to me how one manufacturer (whether they employ iron or aluminum for heads) would recommend using A-S and another not. The process is not brain surgery and would replicate itself mechanically from car brand to car brand. It is either "ok" for all cars or "NG" for all cars IMO. YMMV as always!

It actually would make sense to me if BMW were to say "never use A-S as BMW loves to make $$$ in the repair part of the business and parts.
 

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#1 culprit of plug backing out is inadequate torque.
Recall that people are always worried about over-torquing the plug, but this is unfounded fear because in order to destroy the cylinder head, you have to go to about 100 ft-lb. And even so, the threads are still OK, only the top of the spark plug (the porcelain part) is broken! Find a junk E39 engine and torque the hell out of the plug and see what happens.

Having said that, b/c of over-torque fear, people under-torque ---> plug backing out.

If you want to avoid this issue altogether, then once every 2y or so, remove the plug for inspection and put it back in.
 

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#1 culprit of plug backing out is inadequate torque.
Recall that people are always worried about over-torquing the plug, but this is unfounded fear because in order to destroy the cylinder head, you have to go to about 100 ft-lb. And even so, the threads are still OK, only the top of the spark plug (the porcelain part) is broken! Find a junk E39 engine and torque the hell out of the plug and see what happens.

Having said that, b/c of over-torque fear, people under-torque ---> plug backing out.

If you want to avoid this issue altogether, then once every 2y or so, remove the plug for inspection and put it back in.
And you need not even consider the porcelain part unless your socket does not stay "centered" which is why one should use a socket made for plugs-has a rubber insert to help keep socket aligned and not bumping and twisting to touch porcelain. A straight socket only torques metal. A slip and the porcelain can become cracked. Use proper extensions to be able to stay very straight on plug and use no extension, if possible, for ultimate torque attainment.
 

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Very informative thread!

I exclusively use NGK plugs. My 540, my wife's MDX, my buddys e90, another buddys e36... all NGK.

I always use anti-seize. I have seen first hand what could happen if you don't. As a general rule of thumb, any plug that has anti-seize should be torqued tighter than those without. The anti-seize acts as a lubricant, so I get my plugs good and tight, and then do 1/4 turn more. Never had a problem!

CN90 is absolutely right, every couple of years (or every inspection) check the plugs and the boots while checking the vcg for leaks.
 
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