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Dealer recommended conventional oil?

I had my first change Today on my 2019 CX-9 and they put conventional oil in it and said it was better for the turbo. This blew my mind and sounded completely false. Can’t find anything in the manual either way. I have been using synthetic in all my cars cars for years and I was dumbfounded. Any intel out there on this??

Sorry guys - I found a rather complete older thread on this. Sounds like I can put in what I like - Mazda doesn’t recommend either. Sounds like a dealer thing. Do my own oils anyhow, now that my free one is over, I go synthetic thank you.
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Mazda CX-9 Grand Touring 2016
Dealership service writers have no training in lubricants. They sell what they're told to sell, or they sell what they have the biggest margin on, or they sell based on old shadetree mechanic myths. Trust the owner's manual. Conventional oil is OK. Synthetic is superior for the very cold, the very hot, and lower rate of oxidation (so longer useful life). I use syn in my turbocharged engine.
5w30. Oil is oil just like gas is gas. Putting Chevron 91 doesn't mean your car will better than Arco 91.
That’s not true. You have different base stocks in oil and a bunch of different additives that make up different manufacturers. Some flash at different temperatures and some are more resistant to mixing with gas (best suited for DI Engines).

Gas you have top tier which has a certain certification of additives and a level which it has to be to have the certification.

Mazda CX-9 Grand Touring 2016
"5w30. Oil is oil "

I'm with Brett. All that said, every update to the API service categories (Currently tops at SN+), the ILSAC specs (GF-5), and the manufacturer specific specs (like GM's Dexos) requires better oil so the products that meet the specs are better than previous versions. That's just to meet the spec. Some oils exceed the spec. I use either Castrol full syn or Mobil 1 oils.

New oils to meet the newest specs will soon be on the market. API SP and ILSAC GF-6A (for engines like ours). These will be superior to the older specs and fully backward compatible.

There are bad oils on the market, mainly on convenience store shelves. They either meet an obsolete spec that is not suitable for our engines, API SA up to SM, or the label is OK but the oil is garbage.
Petroleum Quality Institute of America
Here's an example--REV 360 5W-30:
"The results of the tests conducted on this sample do NOT meet the SAE J300 specifications for the SAE Viscosity Grade listed on the product label, and are NOT consistent with the listed API Service Category. The Low-Temperature Cranking Viscosity is nearly six times higher than the maximum viscosity specification for this SAE grade. The Kinematic Viscosity @ 100°C could not be determined due to the presence of water, but is also very likely higher than the specification based on the very high viscosities @ 40°C and -30°C. In addition, the phosphorus content is over five times the maximum level required by the referenced API specification which could cause damage to catalytic converters. Furthermore, the organometallic additive levels in this sample are exceedingly high, potentially leading to excessive piston deposits, and the silicon results indicate the product may be contaminated with abrasive material.

"Use of this product in modern automobile engines will likely cause harm to the engine."
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Anyone using the Castrol Edge European Formula (0w40, previouly 0w30)? That oil has always seemed to be a fairly popular choice in previous cars I've owned (not just the German makes); could have just been sort of a cult following/novelty thing I suppose.
Mazda CX-9 Grand Touring 2016
I'd use an xW-40 oil only during blistering hot summers...Phoenix, etc. Castrol Edge is fine oil, as are many others, but the viscosity needs to match the engineers' recommendations and the operating temperature. In the same vein, I'd use a 0W-20 during frigid winters (and electric engine, transmission, & battery heaters).

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