Sounds easy enough.

 

As you can imagine, there is associated controversy. Assuming a spark plug has 18 TPI, that's about 0.056" per turn. If you need a half turn to get the plug indexed within its range, a spacing washer that lifts the plug 0.28" is required. Some would argue that elevating the plug's electrode this much will interfere with the fuel ignition. I don't know anything about this.

But to install correctly a non-indexed plug, you need to mark the plug where you can see it's orientation, install it and torque to spec, and then see where your indexing mark is. Then, assuming you know where the plug's electrode should be, remove the plug, install a self-retaining washer whose thickness achieves the desired angular correction, and then reinstall and torque. Not rocket science, but worth the effort? Not mine. I'll just pay more for the MB plugs and get the job done.

 

Are you saying that OEM plugs are always indexed to each cylinder?
I'd expect so, since the flame front is critical.

 

Thanks for the explanation.

 

According to the MB technical paper, engine spark plug threads are precisely machined and MB spark plug electrodes are calibrated so that when correctly torqued, proper indexing is assured in every cylinder.

 

Thanks for the video/link. This is for a V6, which is different than the 3.0L IL6 on the 2020 or newer models. I'm hoping someone can create a video on these newer engines. I've yet to find one.

 

Thanks. That's what I thought.

 

Sweet, thanks!

 

You really need to grab a copy of WIS for the procedure on the M256.

 

I'm in the middle of changing my plugs in a 2020 GLS450. I have access to WIS, but I cannot find anything about getting to plug #6 in the back. It is underneath what I assume is the intake to the turbo charger inlet and some sort of actuator.(waste gate maybe?). Below is (should be) a picture of what I am dealing with. That is a rag stuffed into the intake. I've been looking at it and WIS for 2 days and am a bit stuck. ANy help appreciated!!

.

 

Are you sure you drilled down deep enough into WIS? The top level document's right-hand most column references other WIS documents that provide further instructions.

 

I'm not fluent in WIS, but "I think" I have looked at the relevant available documents. I saw a comment on a different forum about task specific notes and Job Cards which may have more, but I could not find those. Here's what I pulled up below. Could I be filtered wrong? Thanks for the quick response,

 

Am always curious, given the known issues with the wiring harness during spark plugs replacement , what would be the implications (if any) for just leaving the spark plugs alone even up to the 100k miles!? Slightly lower MPG? Anything else?

 

Once I was told that they can get hard to remove if left in for a long time.
It kind of makes sense, looking at the amount of thread on the plug, before it gets to the gasket.
I think anti-seize is not used and not recommended.
Haven't verified either of those statements.

 

You seem to have reached the bottom of the "WIS well" with the -1580E and -2003MSC documents which provide the helpful guidance "remove ignition coils" and "unscrew spark plugs". You might just have to nudge stuff out of the way to reach #6.

 

I changed the "100K mile plugs" in my Rubicon last year at 50K, and 3 of the 6 plug electrodes were substantially eroded. The new plugs produced smoother operation and better mpg's. If coils and cables are suspect, do a total changeout.

 

That's exactly what I mean... I feel that 80K or 100K is the right duration, given how expensive this job is, I don't see the need to do it at 50K. Things will be fine at 100K that's assuming the 1st owner will keep it that long. I think we won't keep the car beyond 70-80K miles, and hence, am not planning on doing the 50K spark plug change as am sure they will be just fine at 80K when we are about to let the car go without ever doing spark plugs. I am just not convinced it's worth it to do it twice in the span of 100K miles.

 

I expect to keep my car for 8-10 years. I can't find any other car that interests me now. Part of it is the options I chose, so a similar replacement would cost in the $140k range.Can't afford that.

So (after a favorable oil analysis) my plan is to change the plugs at my next oil service, around 55k miles, get the old plugs to analyze, and we'll see their condition. Both the tip/electrode erosion, and the amount of combustion products that may have creeped up the threads.

Then I'll know if it was premature, or a wise decision.

 

I think that's the right idea. With direct injected engines requiring plug indexing, I would expect sensitivity to plugs being correctly gapped also. An eroded electrode with a gap 2x the spec can't be a good thing. Even if the old plugs look OK, a new set buys 50K miles of confidence. $200 for plugs and a day's work is a good investment.

 

Just following up on my original question with the results. Short answer is that there is a reason they charge so much for a plug change on the GLS450. All of the real effort is in getting to plug number 6, which is a pain in the butt. After disconnecting all of the obvious oil lines, the process included first removing the divert air switchover valve (#1), then the actuator (#2) for the turbo (not proper name), and then the intake air duct (#3) for the turbo before you could even begin to fight with the coil and plug in minimum space. Moving #2 required getting to the 2 bolts underneath the back right side only viewable with bore scope. Then the second bolt on the intake is not accessible from above or below easily and required removal of the wheel well which didn't help that much. I relearned how to use WIS/ASRA though, so I got something out of it. Short story is it may be worth it to have the dealer or experienced GLS x167 Mechanic do it unless you have limitless free time, all the proper tools, a good working knowledge of WIS/ASRA and a lot of luck. Plus be extra careful with the wiring harness which I read is very prone to cracking and breaking ($$). I will not do it again. Makes the LX 600 start to look awful nice... just saying

Access to plug #6

 

Just had mine done at the dealer. $450 was a small price to pay to not have to fight with this setup. So much more complicated than it needs to be.

 

Money well spent. Which dealership did you use? $450 is a steal based on my experiences.

 

Mercedes Benz of Memphis. Had it done with my Service B and 60k transmission service. Had a 2025 GLS450 for a loaner too.

 

What did they charge for the transmission service, if you didn't mind sharing?

 

$750