ayoustin
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- Jul 31, 2018
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Indexing plugs is generally for efficiency reasons when being used in OEM applications. The only other production car I'm aware of to use indexed plugs is the first generation Honda Insight. Honda stamps the cylinder head with a letter by each plug hole for what plug is needed to get the ground strap oriented correctly. I've seen Insight owners say they've had significant changes (a few MPG) in fuel economy going from correctly indexed plugs to non indexed plugs and vice versa. Those Insights are highly sensitive cars though (it gets over 70mpg for crying out loud) so small changes make a big difference, I doubt it would be nearly as noticeable of a difference on one of these trucks.
I'm honestly very surprised to see Ford do this though. I would imagine with modern manufacturing they can get the threads in the head oriented the same for every hole so they don't need to call out different part numbers for different indexes like Honda had to 25 years ago. I'd also wager that most aftermarket plugs won't be threaded the same every time as an OEM plug, so unless you want to mess around with indexing washers stick to OEM plugs.
I'm honestly very surprised to see Ford do this though. I would imagine with modern manufacturing they can get the threads in the head oriented the same for every hole so they don't need to call out different part numbers for different indexes like Honda had to 25 years ago. I'd also wager that most aftermarket plugs won't be threaded the same every time as an OEM plug, so unless you want to mess around with indexing washers stick to OEM plugs.
