So, I know FB25 engines require 0w20 synthetic oil.

 

What are advantages and disadvantages of running synthetic 5w20 or even conventional 5w20 (assuming all the same brand)

 

I'm not asking because I want to run 5w20. I'm asking because I've seen dealer techs using 5w20 in the FB engine and I want to know why.

Obviously most of us know that the early gens of the FB25 consumed oil.

 

So follow up question. Would using a 5w20 actually help reduce oil consumption during warm up because it's 5 and not 0?

And/or does using conventional in theory help reduce consumption at all?

I would stay with synthetic, just run thicker.

 

Probably wasting time and thought with that meager of a change, it'll fair no different.

 

I'd probably try 15w-40 synthetic in non winter/non frigid climates for a thousand miles just to see what happens.

As per the manual. 5w30 is acceptable if 0w20 is not available but 0w20 must be used next change.. The engines are sensitive to viscosity with the vvt systems

Screw that 20 weight fuel economy garbage. Amsoil 10w40 premium protection. It won't hurt a thing. Might eventually wreck the converters but probably not for 100k or so at least. 20 weight is for fuel economy only. There is no design choices in the inside of the engine that requires this thin of an oil. The turbo models of the FB spec 10w30 just like the EJ's. And take it from an engine builder there isn't any difference in the tolerances inside the FB than any other Subaru aluminum block engine. If there were, they would be locked up when cold like a NASCAR engine that hasn't been pre-heated (those really do require 20 weight, after a 4 hour pre-heat to enlarge bearing clearance to running spec). 

 

GD