I would replace both belts any time you change one. The stretchy one requires you take the other off, and you're not doing that on the side of the road without a LOT of cursing and trouble (jack, stands, etc.) Its a pretty quick job in your garage and IMHO its nuts not to change the stretchy one. You break that stretchy one and its an instant overheat and on these engines that risks a cracked cylinder head. For the cost of the belt that's a bad gamble.

As for the tensioner my rule is inspect everything in the path and check for bearing, roller and shock health. If all are ok leave it alone.

Gates is typically a good brand; the stealer has the belts as well and they're not ridiculously expensive.

 

Yes, do all three. No reason not to while you're in there and it's not hard work.

https://www.mazda6club.com/threads/gates-tensioner-newly-installed-rattling-noise.450808/

 

Yes, do all three. No reason not to while you're in there and it's not hard work.

https://www.mazda6club.com/threads/gates-tensioner-newly-installed-rattling-noise.450808/

It

Yes, do all three. No reason not to while you're in there and it's not hard work.

https://www.mazda6club.com/threads/gates-tensioner-newly-installed-rattling-noise.450808/

It looks like that post also used Gates brand, is that what you used?

 

That post had a problem with the Gates part -- and I would never use Gates personally based on experiences with other cars. I have however never used them on Mazdas.

I replaced my tensioner a couple years ago on my 2015 (at about 65k miles) with an OEM one. In this case most of the early Mazda tensioners had a slight oil leak which makes a small mess around the tensioner, and that's the only reason I replaced it, not because it was failing. I put another OEM one on (the revised part). I generally like to keep my cars a long time and replace things once and not multiple times, so I gravitate towards OEM products. However, if you plan on selling the car in the near future you might decide to save a few bucks.

Honestly though, everything I buy from RockAuto usually ends up being crap. I use them for so little these days unless it's an aftermarket brand I trust, which Gates is not. (Usually I only use them on my german car where there are several decent OEM suppliers for any part, not like my Japanese cars.)