Moxostoma

There's lots of information on changing the spark plugs on a C350 out there so I thought I was ready when my Bosch ZR-6-SII-3320 spark plugs and dielectric grease came in.When I checked to make sure I had the correct socket, the 5/8" that everyone said would fit is too big. I measured with my box end wrench set and it turns out that the Bosch spark plugs take a 14 mm 12-point spark plug socket. Why the discrepancy? Are iridium plugs smaller than platinum plugs?

JohnnyC

5/8" is equivalent to 16mm and 14mm is equivalent to 9/16".

Manufacturers often design parts to be not compatible with different versions of the the same machines. In this case the spark plugs are completely different on each engine so you have a less chance to mix up.

Neal W

I got a 2012 C-300 and prepared to change my own plugs soon. I'll use the 5/8'' socket although for mercedes you need a THIN WALL socket.

Hope it will help.

ItalianJoe1

All the 276/278 engines take the 14mm 12 point plugs. Be sure to use the correct ones.

ItalianJoe1

Smaller plugs actually allow more space in the head for better airflow/cooling, as the area that can't be touched for the spark plug thread is smaller. It's a performance/efficiency gain, albeit small, not just to keep them from being swapped with older style plugs.

ezshift5

Italian Joe, you bring much needed sage guidance to this site.

Thanks,


ez

ItalianJoe1

My pleasure, I just try to help where I can and make sure correct information is available. I see FAR too much false info passed around, and i'm a big DIY guy, I'm all for helping people who want to learn and do their own thing. Yes I'm a dealer tech now, but I've been working on my own cars since I was 16 and respect the people who don't have the background I do but still tackle the big jobs.