Best Engine oil for Mazda 3

The gallon of Castrol is the same whether you buy it at CT or Napa.

Could be weather related. I'm in Canada and we have weather from -35C to +35C, so Mazda recommends oil changes every 8000km instead of 12,000km.

SOOOO I've always used full synthetic way before most vehicles started recommending it from the manufacturer. I've ran mobile 1, royal purple, and a few others. When we got our 2007 Mazda 3 all of the records/receipts showed conventional Castrol was used. I've stuck with it to see how it do... I've increased the weight "one step" because we live in a hotter than average climate but we just hit 290k miles with not major issues... my average MPG is 31.x and I typically do 10 over the speed limit (so it could definitely be improved).I change it myself every 5k miles. I think the frequency is more important than the quality with oil. I'd rather have super tech every 3k than mobile 1 every 10k. I think if you stick with any major brand, use a good filter, and change it regularly you'll be fine.

I use Castrol Edge High Millage and a STP XL filter or Mobil 1.

I use Madza OEM filter with Pennzoil Ultra Platinum 0W-20 every 8,000 km to 10,000 km.

I personally like the Pennzoil over the Idemitsu high moly oil but it's mostly due to being more available in my area.

I do think the Pennzoil is slightly better fuel economy wise and comes out cleaner than the high moly but this is probably a placebo than anything.

The oil was Idemitsu Synthetic 0W-20 with 12.5k miles on it. Once again, trace metals and flashpoint were within normal range. I also ordered a TBN to measure the amount of additive left and that showed there was still plenty of active additive remaining.

I've always had great luck running 0w-20 Mobil 1 through my 2012 skyactiv. Regular changes through 130k and counting.

Eneos 5w-20 in my 2008 2.3 liter Mazda3. It's a Japanese-branded synthetic oil that you can get from Napa Auto. I've found that with Eneos, my Mz3 stops consuming any oil (in both my 2007 and 2008 2.3's).

Although this is exact replacent, mazda OE still uses Mazda branded GF-5 which is exactly the same oil but branded Mazda....

Love these high molly low viscosity oils. Absolutely the best out there

That's the wrong oil. You want the Idemitsu eco gold medalist advanced moly 0w-20, which is basically the same as Mazda oil(Idemitsu makes the mazda oil).