Replace Spark Plugs


Here a quick guide on how to replace Spark Plugs for 272/273 engines. The car I replaced it on was a 2008 C300 Luxury (also did it for a friend’s 08 ML350). It is recommended that you replace spark plugs every 5 years or 90k miles (whichever one comes first).


Required items
• 6 Spark plugs (I got NGK Laser Platinum PLKR7A 4288)
• Anti-Seize Thread Lubricant
• Torque wrench
• Wrench Extensions (multiple lengths)
• 5/8’ Spark Plug Socket: the only difference between a normal socket and spark plug is that the spark plug socket has a built in magnet that prevents the spark plug from falling back into the engine (I highly recommend getting it)
• T-30 Torx Bit Socket
• Flat Head Screwdriver


Procedure
1) Remove the air intakes and the engine covers. For the intakes, use the screw drive to push in the clips holding it to the grill assembly. The rest you can pull off (might need to put in some force if you haven’t opened in for a long time)


2) Using the T-30 Torx Bit Socket, remove the two screws that hold the wiring for the spark plug. After removing the screws, you will have to pull a little hard since it almost like a vacuum holding it in.


3) Using extensions and the spark plug socket reach into the engine bay and open the spark plug. They were a little stuck at first but after a few spins they come out easy.

4) Open the new spark plug and apply a little Anti-Seize Thread Lubricant to the threads. The small packet in the photo above lasted me all 6 spark plugs.

5) Insert the new spark plug into the socket and put it back into the engine. Tighten the spark plug. First tighten the new spark plug with your hands until your hands cant tighten it anymore, then move to the torque wretch. When tightening the spark plug, set the torque wrench to 17lb/ft (23Nm).
6) Put the wiring harness back on top of the spark plug. Tighten the screws that hold in place. When tightening the screws for the harness, set the toque wrench to 10lb/ft.
7) Repeat steps 2-6 again for all the spark plugs
8) Go around to all the harness screws and double check they are tight to the right specifications (10 ft/lb).
9) Attach the engine cover back and install the air intakes.
10) Done!


This is an easy job for any DIY’er. I spent a total of an hour doing all of this. The dealer wanted $350.00 for this service and I did everything for around $90.00. The spark plugs were $13 each (factory oem).

Please feel to post your comment and questions and I can try to help answering them.

Thank you,

 

Great post! Thanks for taking the time!

 

Nice how-to, thanks. I was not able to find whether or not the plugs in our 350 were changed at the 5 year mark so they are on the list to be replaced when I do the next service and this will come in handy.

Something I recently learned about NGK plugs is they do not require anti-seize due to their coating process. I wish I had known this years ago for the NGK plugs I have installed but living in the aviation world for so long ingrained the use of anti-seize in my brain. This may/may not apply to other brands but something to consider when using NGK for replacements.

From their spark Plug 101 section...
"1. Anti-seize

NGK spark plugs feature what is known as trivalent plating. This silver-or-chrome colored finish on the threads is designed to provide corrosion resistance against moisture and chemicals. The coating also acts as a release agent during spark plug removal. NGK spark plugs are installed at the factory dry, without the use of anti-seize. NGK tech support has received a number of tech calls from installers who have over-tightened spark plugs because of the use of anti-seize. Anti-seize compound can act as a lubricant altering torque values up to 20 percent, increasing the risk of spark plug thread breakage."

http://www.ngksparkplugs.com/about-n...ut-spark-plugs

 

Yep, don't use the copperpaste

 

Word of advice, when installing the plug don't put the torque wrench on the extension until the plug is screwed all the way in. Head threads are easily stripped. Best procedure is to put the plug in the hole, turn backwards (counter clockwise) until you feel the threads drop into engagement and then finger tighten all the way into the head. Only then put the torque wrench onto the extension.
In the old days, plug sockets had rubber inserts rather than magnets because the heads were iron.
Nice job with great pictures.

 

ickdeep, nice write up. Thanks for taking the time to do this

ibcrusn, important tip -- thanks for reminding me.


I know that plugs come pre-gapped, but I always check the gap just to be sure. Anyone know what the gap should be?

 

Great write-up, thank you. How often should the coil packs & cables be replaced?

 

When they break

 

Fantastic post, thank you!!

 

I have a 2014 GLK350 4Matic which from the post above seemed like it would be a fairly straight forward and easy spark plug change. However, my motor looks nothing like the one above. Front little panel does pop off easily enough but the back part not so much. Not sure how to access or get to the spark plugs. VIN# WDCGG8JB4EG287246. My thoughts are mine will not be an easy DIY project to replace the spark plugs is that an accurate statement?

 

Did this my self 2 years ago, everything works fine by then and saved me a lot money.

 

U need to find some videos on YouTube there are plenty of good instructions online!

good luck!

 

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Hi there,

Please see post#10 with a guide on how to replace and index spark plugs on an M276 engine:

https://mbworld.org/forums/c-class-w...ce-thread.html