Lots of great info in this thread but I wanted to add a bit of data as confirmation of various points already made.
I just spoke with NGK tech support to confirm that plugs I bought from Amazon (direct, not a marketplace vendor) were authentic.
I've started to do this more and more with parts I buy online since cheap fakes are everywhere.
Here's what I learned:
1. NGK is absolutely the OEM for the Mazda CX-5 2.5L plugs you'll buy at the dealer for this vehicle (and most other Mazda plugs).
2. ILKAR7L11/94124 is the correct NGK part number for the 2.5L engine even while it does not have the double tip design like the Denso that some have seen in factory plugs.
3. While not currently an official retailer, NGK is in talks to add Amazon to the official list currently occupied by familiar auto parts retailers so we know the supply chain in place.
About Fakes:
There are lots and lots of fake spark plugs out there that come in nice boxes and look pretty good until you get picky.
If the price seems too good to be true, run.
After talking with NGK about the markings, packaging, etc. we confirmed as best we could over the phone that the plugs I bought from Amazon are authentic.
NGK's main points were that if you paid a reasonable price (I paid $12.89), and the manufacturers lot date code stamped on the hex part of the plug was in their books, the plug was likely okay.
Another item to check was that the washer does not come off and matches the size of the plug.
The ground electrode on the NGKs are very precisely welded and line up perfectly with the center tip.
My plugs are stamped "M714" which stands for the plant (Minamiyama, Japan), the Year (...7), and the week code (14 = April 3). NGK said that that code checks out as an actual manufacturing lot on their books.
NGK stated that the box should also state "Made in Japan" in several languages. Russian characters on the box are a good sign as that is their new labelling standard.
Here's a link to NGK's guide to spotting fakes:
http://www.ngk-sparkplugs.jp/english/techinfo/fake/index.html
My Experience:
I tried the cheaper Densos and they did not perform as well as the factory plugs or these NGKs. I have no instrumentation to backup that claim, so YMMV.
FWIW, the NGKs all Ohm'd out at slightly above 5k Ohms and were very consistent, while the Densos were more variable and around 4k Ohms. Both numbers are within the spec of 3.0—7.5 k Ohms.
Here are some pics of the 4 new NGKs and a side by side of the Denso plugs I only ran for around 1500 miles. You'll notice that design of the 2 plugs places the spark at every so slightly a different depth in the cylinder. I can only speculate what kind of difference that might make.
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