Garagebuilt

I’ve exhausted all research. Is the part number for these PLKR7A? All I’m finding is Bosch and Denso. Thank you

Mud

Those are equivalent to Bosch YR7MPP33 as stock replacement in my V6.
Stock Bosch number is different for your V8 so I don't think those NGK are correct for your car. Unfortunately I don't know which NGK are applicable, perhaps a 550 owner will have info.

Garagebuilt

Yeah i didn’t think they are. I found these as well SIZKBR8A8HS but i have never found so many dead end answers than i have on NGK’s.

konigstiger

PLKR7A is the only one listed in NGK catalog. Why not OEM 0041598103 or equivalent Bosch, see attachment.

Arrie

AutoZone lists 3 NGK spar plugs for the E550.

LKR7AIX for $8.99
PLKR7A for $13.99
LKR7BGP-8 for $4.69

The middle one is what I got from AutoZone. They are kind of expensive for a spark plug but NGK plugs in my opinion are the best you can get. I'm sure other plugs work too but Mercedes also had these plugs in my car from the factory.

The last on the list is not available by AutoZone net site. Don't know why they even list it.

Mud

I'm sure those plugs will work but I'm always a little leery of what AZ lists to fit from previous bad experience with them.
My concern in this case is that the oem Bosch numbers are different for E350 and E550, leading me to believe that heat range or plug indexing/reach into the combustion zone may be different. The PLKR7A are listed by a variety of vendors as fit for the E350 but I'm just not sure about the 550.

Arrie

I have them in my car and these are in the car manual too. But mine is pre-direct inject so it does not need indexing.

Mud

Arrie, I had found out from one of the MB techs here that even the pre-direct injection engines (mine is pre direct injection) require proper indexing.
I had always thought that plug indexing was limited to hi performance or race cars but I found his info enlightening. I'll see if I can find it somewhere.
I'm not saying that the engine wouldn't run but from the info I saw MB went to great lengths to ensure the electrode was in a particular position within the combustion chamber.
For all I know it may be the same with these NGK plugs, but again I hesitate about the different part numbers for oem plugs between V6 and V8.

EDIT - Arrie, you may be correct for the non-direct vehicles. Here's the post about it, as related to direct injection:
https://mbworld.org/forums/e-class-w...zing-fact.html
Apologies for posting before verifying

However, the nagging part to me is still on the oem part number difference between V6 and V8, may be related to depth of threads and heat range.
May seem like splitting hairs but after seeing several engines with piston "pings" from wrong heat range of plugs (too high) it may worth a second look.

belarus27

yep ngk