Has anyone done this themselves? Any pointers would be appreciated. I've changed spark plugs before, but not on this rig. Took a look under the hood, and I can't even see the spark plug wires. Do I need to access from the wheel wells?

 

to get at the plugs.
The plugs are 5year /100k mile units.
No need to change the wires.
Is your engine part of that class action lawsuit?

 

Surely you wouldn't attempt this without reference to factory procedures.

Mercedes makes this easy for you: http://www.startekinfo.com/StarTek/o...tedDocId=11498

DIY means you do it. It does NOT mean you do it without proper knowledge and tools and the investment that requires.

Have you checked your maintenance booklet to determine the replacement schedule? I have, it's 60K miles or 5 years for this engine (Ohlord confuses M272/3 with M112/113)

And, BTW, there are no "sparkplug wires."

"Class action lawsuit" is for very earliest M272/3 and not applicable to GL450, as those engines didn't arrive until 2007. It's a lawsuit that's going nowhere in any event, but if you do own a 2005-6 model I'd worry about the balancer shaft/cam gears.

 

for the info. I though the o7 273 was included.

 

'07 GL450 spark plug was the easiest plug job I've ever done.

1) Take off the sway bar, plastic covers, etc just like you are doing an air filter change

2) You'll see all 8 plug boots - none are in tricky places. Carefully pull off the rubber boots to expose the plugs.

3) Remove old plugs with an appropriate socket. I used one of the hinged ones and it helped get to the back right plug. Socket costs about $6 at Sears

4) Insert new plugs and tighten with appropriate torque. I used Bosch plugs and the torque was listed on the side of the box. Some people put in anti-seize lube here ... your call ... if you plan to change again in another 100k, might as well

5) Carefully push the boots back on the plugs

6) Reverse #1 - make sure to get the MAF tightly covered when you put the filter box back on. Also make sure that the crossbar is very tight, otherwise you'll get a rattle

Nice job ... you saved yourself a few hundred bucks.

 

Pretty simple. One is, above, it's not the sway bar. It's a cross brace. Also, the coil tops are held in place with T30 bolts. They don't just pull off.

It's a great service to combine with changing the air filters.

But I ran into a couple of difficulties.

One is, there was some sort of rubber debris, like portions of rubber flange, in several of the spark plug wells. I'm pretty sure it came off the coils.

The other was pretty much heart stopping. When I installed one of the spark plugs, as I was torquing it down, I felt it "give". Now, anybody that has wrenched knows what it feels like when threads strip. This freaked me out, because I simply didn't push that hard on the wrench; it's a 3/8" ratchet and I'm not THAT strong. I backed the spark plug out, my heart pounding in my ears, getting ready to see aluminum cylinder head material in the spark plug threads.

The threads were clean. I peeked in the spark plug well, and saw the rubber debris at the bottom. I figured that what had happened was the rubber had gotten in the way, and the "give" I had felt was the rubber getting squeezed out of the way. I vacuumed the rubber debris out of that well and the others and went back to installing the spark plugs. This time, one spark plug simply didn't accept torque, and spun freely. I pulled it back out to see this:





So, yeah, the spark plug came apart, leaving the threaded portion stuck in the cylinder head. Again the heart is pounding in the ears. Getting creative with a screwdriver, I managed to unscrew the separated thread piece out of the cylinder head. I put one of the old plugs back in to one of the front cylinders, and I'll order a replacement.

So, bottom line is this:

1. You may need to clean the spark plug wells. Mine had rubber debris in them. Inspect them with a flashlight and a mirror (to see the back cylinders).

2. Be careful with the torque! I have never in my life over torqued a spark plug to the point of self disassembly, but here you go. I applied more torque to remove the plugs than I did to break the threads on this one. Maybe defective, but they are kind of skinny ... I dunno. Maybe the rubber debris distracted me from the torque process. The box had no torque spec on it, contrary to the above. Yes, they are Bosch plugs.

Hope that helps, y'all. Carry on.

 

Could someone please verify the number of spark plugs needed to do this job on GL450? Do I need to buy 8 or 16 plugs?

Thank you in advance!

 

Eight.

Remember, watch that torque! Them plug threads stretch right apart mighty easy.

 

That pic reminds me of the plugs that break off on Ford trucks.
Anytime you change spark plugs down in a well, always vacuum out the hole before removing the plug. A slightly warm engine helps also!

 

is the same process for 2012 GL450 4matic US Version?