Spark Plug Cross Thread Question
Thread Starter
Newbie
Joined: Aug 2025
Posts: 4
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2018 GLE350 4Matic
Spark Plug Cross Thread Question
I have just finished installing 6 new plugs and coils in my 2018 GLE350. No major problems came up during the installation, with the driver side plugs being the most time consuming to get in.
Drove the car 100 plus miles since with no issues, feels smooth, and no codes stored.
My question is this, especially for the #6 plug as it was almost impossible to see into, how easy is it to cross thread a spark plug? All plugs were started by hand, and then switched to a ratchet there after. While I did encounter minor resistance, all six plugs went in with relative ease and all torqued down to spec.
I guess I am concerned given the lack of visual confirmation for the driver side plugs. Would there be ignition symptoms if a plug was cross threaded? Or can a cross threaded plug last for the entire service interval?
Drove the car 100 plus miles since with no issues, feels smooth, and no codes stored.
My question is this, especially for the #6 plug as it was almost impossible to see into, how easy is it to cross thread a spark plug? All plugs were started by hand, and then switched to a ratchet there after. While I did encounter minor resistance, all six plugs went in with relative ease and all torqued down to spec.
I guess I am concerned given the lack of visual confirmation for the driver side plugs. Would there be ignition symptoms if a plug was cross threaded? Or can a cross threaded plug last for the entire service interval?
Member
Joined: Feb 2025
Posts: 135
Likes: 47
I have just finished installing 6 new plugs and coils in my 2018 GLE350. No major problems came up during the installation, with the driver side plugs being the most time consuming to get in.
Drove the car 100 plus miles since with no issues, feels smooth, and no codes stored.
My question is this, especially for the #6 plug as it was almost impossible to see into, how easy is it to cross thread a spark plug? All plugs were started by hand, and then switched to a ratchet there after. While I did encounter minor resistance, all six plugs went in with relative ease and all torqued down to spec.
I guess I am concerned given the lack of visual confirmation for the driver side plugs. Would there be ignition symptoms if a plug was cross threaded? Or can a cross threaded plug last for the entire service interval?
Drove the car 100 plus miles since with no issues, feels smooth, and no codes stored.
My question is this, especially for the #6 plug as it was almost impossible to see into, how easy is it to cross thread a spark plug? All plugs were started by hand, and then switched to a ratchet there after. While I did encounter minor resistance, all six plugs went in with relative ease and all torqued down to spec.
I guess I am concerned given the lack of visual confirmation for the driver side plugs. Would there be ignition symptoms if a plug was cross threaded? Or can a cross threaded plug last for the entire service interval?
Im sure you would have known if you cross threaded one of them. It takes quite a bit of torque with the ratchet if it’s cross threaded.
Super Member
Joined: Oct 2012
Posts: 538
Likes: 88
From: Hollywood, CA
W209, W124
Cross threaded one in a Big Block Chevy once. Ran fine then one day I got on it and the spark plug shot out like a bullet. Car made a hell of a racket. Got a new plug and all was well. Cast iron heads.
Thread Starter
Newbie
Joined: Aug 2025
Posts: 4
Likes: 0
2018 GLE350 4Matic
Sounds fun. So you didn’t notice the plug had been cross threaded when installing?
Super Member
Joined: Oct 2012
Posts: 538
Likes: 88
From: Hollywood, CA
W209, W124
I was 16 or 17, first time changing plugs. The car was crusty with rust and oil crud. The plugs had anti-foulers on them so went in weird anyway. I didn’t notice but paid much more attention from then on.
