Spark plugs...SP578 CYFS12YRT3 versus SP594 CYFS12Y

[Msfitoy]

I can't seem to find a definitive answer...is SP594 CYFS12Y ok to use?

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[Apples]

The 578 is the correct one. This said, there is a replacement number (594?). In any case, I'd check with your dealer's parts folks.

 

[Msfitoy]

The 578 is the correct one. This said, there is a replacement number (594?). In any case, I'd check with your dealer's parts folks.

This is what's on order...confusing right?

 

[deleriumtremor]

This is what's on order...confusing right?

I think the 594 is the max endurance plug "Ruthenium", whatever unobtanium element that is, IDK?. The 578 is the Iridium version. Just FYI, Rockauto is about 25% less than what you have pictured on Amazon for the 594 plug. Of course, you have to get more stuff to justify the shipping versus AMZN.

 

[Msfitoy]

Found it...from 5 Star Tuning:

" Part number SP- 578 has been superseded by Part number SP-594"

https://5startuning.com/product/201...torcraft-iridium-spark-plugs-set-of-6-sp-594/

 

[4rd SVT]

Throwing a "wrench" into this conversation...

Tune+ NGK 1-Step Colder Pre-Gapped Spark Plugs

I have a set in my RS, and seems to ide & drive smoother...
My plan is to order a set & at some point, swap these in.

I'm gonna contact them to see if there's a difference in gap for the Ecoboost-Mustang & RS version of the 2.3L specs... so I know which version to order.

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