https://www.mazdausa.com/siteassets/pdf/owners-optimized/2016/mzd6/2016-mazda6-owners-manual.pdf
Starting on page 6-27
0w-20 is the preferred oil in the US and Canada. That vis is not required; it's "recommended". They also recommend Castrol; do you use that?
They also spec 5w-30 for that same engine in Mexico and just about everywhere else on the planet. They also state that 5w-20 is acceptable if 5w-30 is not available.
IOW, any decent API certified lube between 0w-20 and 5w-30 is OK to use in that engine. You'll get ever so slightly better fuel economy using the thinner grades, obviously.
This is not a new topic; it gets played out with just about every brand of OEM and the owners of their cars.
Could Mazda give you a hassle if you didn't use 0w-20? Sure they can. But ultimately it comes down to the understanding of warranty provisions and burden of proof in the M/M Act.
Mazda does not even both developing their own oil spec; they just say "use what's recommended". (page 9-4)
Basically, as long as you use an API SM or better, in a vis between 0w-20 and 5w-30, you're good.
And when was the last time we saw a Mazda engine implode because of vis grade, anyway?????
It's not like being in KY induces temps so cold that you need a 0w rated lube, or it's so hot that you must have a syn to avoid coking the oil.
Should I believe that 0w-20 is a pure necessity in El Paso, TX, but right across the border in Juarez is totally OK for dino 5w-30? What is it that happens to oil requirements when you cross the Rio Grande???
I could certainly understand 0w-20 being of benefit in the northern part of Alberta or Manitoba in winter, but come on now ... KY is so cold that we "need" a 0w rated syn? Give me a break.
You could easily find a house brand dino lube in 5w-20 or 5w-30 for less than $2.99. RK oil is $1.69/qrt; about half what you're paying. And I've run 10k mile OCIs repeatedly on that stuff; UOAs always come back as good as any brand name syn.
You are NOWHERE near anything close to poor wear rates. Even if you ran out to 15k miles, your wear would be just fine. There is tons of data to show that wear trends generally decline out to 15k miles, for just about every engine family I've ever studied. And I didn't say to run the oil until things went "abnormal" (your word). I said to run it until the wear rate goes above normal trends. As a generalization, wear rates start around 3ppm/1k, and then decline; this is a mass generalization. Your engine already super low in the wear rate. If it upticks above it's unique rate, it's still WELL WITHIN the macro normal trend.
For example; my old 4.6L engines ...
https://www.bobistheoilguy.com/forums/ubbthreads.php/topics/4389122/5
I ran 10k mile OCIs, using both house brand dino (RK 5w-20) and band name syn (Peak 5w-20).
Wear rates for all tests fell WELL inside of "normal" bounds. The average Fe wear rate across 550 samples is about 3ppm/1k miles. Yet both oils I used ran anywhere from 1ppm to less than that! And that is including the dino oils!
If you have not yet read this, please do, so you understand the true relationship of micro and macro data in terms of UOA interpretations:
https://www.bobistheoilguy.com/used-oil-analysis-how-to-decide-what-is-normal/
I certainly understand one's fear of ruining an expensive investment; I get it. But real world data shows that generally we grossly over-maintain things like cars, because of fear. Once you understand what the real data tells you, that fear should subside and common sense should take over. Even if your wear rate doubled (from 1ppm to 2ppm per 1k miles), you'd still be WELL below any condemnation level for wear rates. Wear rates for your engine family can EASILY sustain 3-4ppm/1k miles and yet live to 300k miles or longer. THAT is what macro data analysis tells us.
I will put my money where my mouth is ... I'll challenge you to try an experiment and I'll pay for it if the data comes out worse than macro data expectations.
You run two successive API SM/SN 5w-20 or 5w-30 dino 5k OCIs, with the UOAs. I expect you to drive typical of what this current UOA represents; don't do odd things or use additives, etc. Just follow your daily life.
If the data in the UOA falls outside of macro data "normal" as defined by true statistical analysis, I'll reimburse you for the costs.
I'll even be willing to put the money in escrow; I'll send funds to a mutually agreed third-part BITOG member who'll hold the funds until the experiment is over.
If I'm wrong, you get the money. If I'm right, I get my money back and all you have to do is admit that reality speaks volumes.
Yes - I am that confident I'm right about this.