The fa20dit recommends 10w30 and our manual says to run a higher viscosity in extreme driving situations but never states a viscosity. The fa20dit wrx also recommends a 30 weight. @Kronos

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While this is true, it is not the exact same motor. It could have different bearing clearances to go with the lower compression ratio.

Because turbo problems.

I believe it calls for 5w-30 on the 2015 WRX user manual?

Yes the manual does. And bearing part numbers are the same.

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Being the same bearing spec with a thicker oil makes me not feel bad for using 5W20 with the last oil change.

How about Octane 100 fuel?

It contains only 10% added ethanol, would this require any further maintenance?

These cars like almost all cars these days are designed for 10% ethanol fuels even says so in manual, in some places 10% or more ethanol fuels is all you can get, will be fine.

I suspect the buildup on injectors when running e85 reported sometimes is likely due additives as pure ethanol is a very clean burning fuel.

Here is what the Manuel says word for word regarding engine oil if anyone is interested.

Attachment 80676Attachment 80677





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Also @Reaper I would love to hear the results of the UOA you submitted using the amsoil dominator 10w30 when you get them. I'm hoping it's a safe solution for long term e85 users.


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Noticed my brz manual is different and states 5w30 and 5w40 suitable and even shows in chart will post up scan , been using 5w30

It also says to change it back to 0W20 on the next oil change.

im reasnobly confident they only say that for fuel economy emmisions purposes, i am happy to trade that for long gevity of the engine internals in a hot climate under high load conditions, that htey recomend 5w40 and also in the dit fa20 suggests that the motor is quite capable of using that higher viscosity oil, the 5w will still allow starting in sub zero conditions which i never get :D

True true.