Is "synthetic blend" a legal term to use a cheaper oil?

I know Subaru "requiring" Synthetic oil changes have wiggle room in the O.M.
Hidden somewhere - purposefully, so dealers can up-sell their "Subaru Genuine Synthetic Oil" -
is the statement that the use of Conventional oils will provide adequate service
with no harm to the engine.

In my 2018 Outback owner's manual it says to fill it with full synthetic 0w20 and in the event of oil consumption you can top of with conventional 5w30 if one so chooses.

I have been looking into Castrol oils recently to decide on what to use in that 2018 Outback as well as a 2012 Hyundai Accent and 2004 Chevy Venture. I am thinking SP Edge High Mileage 0w20 for the Subie but can quite decide on which Castrol 5w30 to run in the Hyundai and Chevy.

Ultraclean and GTX High Mileage look good for the price BUT I could spend a few more bucks and get Magnatec BUT then again I could spend a few more bucks and get Edge High Mileage. What is really "worth it" if I am just looking to clean up two old, high mileage engines both with an OCI average of about 4000 miles?
 
In my 2018 Outback owner's manual it says to fill it with full synthetic 0w20 and in the event of oil consumption you can top of with conventional 5w30 if one so chooses. ...
The term " Fully Synthetic" is absolutely meaningless in terms of Approvals. If it meets or exceeds ILSAC GF-5 or 6
It is adequate . In a Subaru 2.5L I would run something more robust than a 0W20. That may be a 5W20 or a 0W20 with some 0W40 MB228.5x added in for a bit of HTHS and package boost.
If you dig deeper in that manual you will likely see the allowance of "conventional oil" hidden somewhere.
Thankfully my used - but new to me 2012 EJ253 OM "allows" 5W30 at the lightest and warns to use a beefier oil where required. Up to 20W50. CAFE standards set that 710 fill cap F.E. oil recommendation.
You have to read between the lines.
 
The term " Fully Synthetic" is absolutely meaningless in terms of Approvals. If it meets or exceeds ILSAC GF-5 or 6
It is adequate . In a Subaru 2.5L I would run something more robust than a 0W20. That may be a 5W20 or a 0W20 with some 0W40 MB228.5x added in for a bit of HTHS and package boost.
If you dig deeper in that manual you will likely see the allowance of "conventional oil" hidden somewhere.

So do you think that a synblend 0w20 would be okay as a primary fill oil in this engine? I don't, I would happily fill with Magnatec 0w20 over Ultraclean 0w20 for a few bucks extra and think nothing of it, I would spend even more and put Edge or Edge EP in before I would consider a synblend.

And I have read the OM thoroughly and the most it allows for is a conventional 5w30 or 5w40 as makeup oil with a recommendation for an oil change soon after adding such oil. I have filled my engine with both synthetic 5w20 and 5w30 both of which caused the drivetrain to perform rough and poorly.
 
And I have read the OM thoroughly and the most it allows for is a conventional 5w30 or 5w40 as makeup oil with a recommendation for an oil change soon after adding such oil. I have filled my engine with both synthetic 5w20 and 5w30 both of which caused the drivetrain to perform rough and poorly.
So changing from an oil with a 0W winter rating to one with a 5W caused your "drivetrain to perform rough and poorly".

In thread after thread the manifold things that are attributed to an oil's winter rating continue to amaze me.
 
So changing from an oil with a 0W winter rating to one with a 5W caused your "drivetrain to perform rough and poorly".

In thread after thread the manifold things that are attributed to an oil's winter rating continue to amaze me.

Put aside your condescension and consider that this specific engine and its drivetrain components were developed to operate and react around the premise that 0w20 was the oil intended to be used. I experimented using 5w20 and 5w30 and related my findings, if you have not done what I did than it would not be best to adopt a presumptuous attitude.

Similarly I had an Audi that had Mobil 1 5w40 TDT (turbo diesel truck) put in it by some ignoramus at a European vehicles shop and that oil caused the engine and drivetrain to respond poorly, so did gas less than 91 octane. When I switched it out to the Audi approved Mobil 1 0w40 everything went back to normal, perhaps surpringly to some everything worked as well as intended when I used the recommended 91 octane gas.
 
Put aside your condescension and consider that this specific engine and its drivetrain components were developed to operate and react around the premise that 0w20 was the oil intended to be used. I experimented using 5w20 and 5w30 and related my findings, if you have not done what I did than it would not be best to adopt a presumptuous attitude.

Similarly I had an Audi that had Mobil 1 5w40 TDT (turbo diesel truck) put in it by some ignoramus at a European vehicles shop and that oil caused the engine and drivetrain to respond poorly, so did gas less than 91 octane. When I switched it out to the Audi approved Mobil 1 0w40 everything went back to normal, perhaps surpringly to some everything worked as well as intended when I used the recommended 91 octane gas.
Like I said the amazement just keeps on going.
 
No sense getting syn blend IMO. You'd be better off saving your money and getting "conventional" that meets the spec, it's probably a syn blend anyway. Oil labeled "synthetic blend" could have a legitimate 50% synthetic content, or it could be just a thimble full. Some brands will state the synthetic content on the label but most do not. As long as there is *some* synthetic content, it's not fraud and they can't get sued. So it's just not worth bothering IMO. You'd be better off buying conventional and synthetic of the same brand, then mixing it yourself :D (This is what I do with my dirt bikes, half Rotella T4 and half Rotella T6 because using all T6 synthetic makes the shifter feel notchy.)
 
The way I see it - there is basically no Conventional oil anymore and also there is no such thing as true 100% Synthetic oil, all are various concentrations of a mix/blend.
So I choose oil that is proven to perform well for my application and is reasonably priced. There are some I like and some I dislike as far as brands go but that's a different story.
Lately, I like to use (all in 5w-30) Valvoline Daily Protection (which is a syn blend), Pennzoil Platinum, Supertech Full Syn, M1 HM.
I always try to get oil while it's on sale and usually have 4-8 jugs on hands at any time since I maintain 3 cars. Sales run every so often so I don't need to stock up for next 5 years while a year worth of changes is reasonable.
 
So changing from an oil with a 0W winter rating to one with a 5W caused your "drivetrain to perform rough and poorly".

In thread after thread the manifold things that are attributed to an oil's winter rating continue to amaze me.
A generally true statement regarding all season multigrade, but I have come to notice that the Asian automakers 0W20 is oftentimes a MUCH lighter oil than a "Ford Style" 5W20.
Subaru Idemitsu show a surprising light KV40 at one point it was 37cSt. Its likely in the mid forties currently with 0W16 taking up the supper skinny banner.
 
When I bought a new car in 2010 the dealer offered $20 oil changes for the life of the car. Of course they use this as a was to get the customer back in for an upsell but I always wondered how much a synthetic oil change at $20 cost them. I just noticed that what they actually call it is a "synthetic blend". Is this just as way to use a cheaper oil or is a blended oil better in some circumstances?

A bit of history on 'Blends.'
After Group IV and V synthetics became widely available it was found that Group I and II base oils could be improved by adding a percentage of Group IV and V synthetic oils.

In the '80's and '90's, the customary 'Blend' formulation (or 'Parasynthetic') contained up to about 25% of Group IV PAO with a small percentage of diester for improved seal conditioning.

With the advent of Group III, and it being accepted as a synthetic oil, a 'Blend' can now contain anything from Groups II through IV.

My finished 'Blends' have an average of 25% PAO with Group II and a small percentage of other base Groups, but I cannot vouch for what today's 'Blends' contain as found on any store shelf..
 
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