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Discussion Starter #1
I live in nothern virginia and bought a 2018 Outback 3.6R and now have 2800 miles
on the clock and getting ready have the oil changed according to the severe usage
schedule of 3000 mile intervals.

Every reference from subaru is either Conventional oil or Synthetic oil.
I would like to use a third oil choice (Synthetic Blend oil).
I have heard that the H6 enging is not designed for full synthetic oil and may have
oil consumption issues with it.

The Castrol website shows the GTX 5w30 Ultracleen as a Synthetic blend, but the bottle does not.
(perhaps it is just a little blend and they still want to sell as Conventional oil).
The Castrol website and the oil bottle whows the GTS 5w30 High Milage as a Synthetic blend.
Both the GTX 5w30 Ultracleen and GTX 5w30 High Milage are API SN Resource Conserving and ILSAC GF-5.


Anyway, I changed out the factory fill break-in oil at aprox 1600 miles.
Replaced with to Castrol GTX 5w30 Ultracleen.
I figure that the GTX 5w30 Ultracleen is close enough to conventional to continue any remaing break-in
of the rings (using the shifters more, up and down WV hills using the engine for downhill deceleration).

I want to switch to Castrol 5w30 High Milage oil (a Synthetic Blend oil).
It bothers me that they promote it as High Milage (75000 mile).
I like that it is a thicker 30 weight oil
30 weight range is 0.3 - 12.5 cSt viscosity at operating temp 100 C.
Idemitsu 5w30 Synthetic = 10.79 cSt viscosity at 100 C.
Idemitsu 5w30 Conventional = 10.94 cSt viscosity at 100 C.
Castrol GTX 5w30 Ultracleen = 11.0 cSt viscosity at 100 C.
Castrol GTX 5w30 High Milage = 11.7 cSt viscosity at 100 C.

Should I be concerned and not use Castrol GTX 5w30 High Milage oil in a not so high milage car ?
 

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I simply cannot abide useless people.
2006 2.5i and 2002 3.0 wagons.
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12,306 Posts
I have heard that the H6 enging is not designed for full synthetic oil and may have
oil consumption issues with it.
Nonsense. Use whatever you want that meets the specs Subaru requires, which is a simple API SN rating.
 

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2016 3.6 Limited with ES
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2,692 Posts
+87 to what AWD said.

Please don't waste your money on a semi syn oil. You have no idea what percentage of the blend is syn and you will never find out. Is it 1% or 15%?

Just run a conventional or syn and call it good. SN rated from Walmart is as deep as you need to go with this.
 
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2015 Outback Limited 3.6r
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3.6r H6's Ships with Conventional recommends Synthetic, may run on either. Says right in the manual, quite a few threads on the topic as well.

The Outbacks aren't expensive enough for something as trivial as engine oil to be of large concern. The longevity of the engine will most likely not be hindered by blends, or incorrect oil. The biggest thing to worry about is timely changes.

If your car is your investment, then by all means there is no harm in research, but the many power users here will recommend what Subaru specifies.
 
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