Application you say.
But I thought UK "specialists" don't know anything.
So why do Cosworth recommend 15w50 on their modified short blocks?
Why do ScoobyClinic advise 10w50 on standard and modified Subarus ?
Why do RCM specify 15w50 on modified and and standard Subarus?
The reason I mentioned the Gobstopper is nothing to do with oil specs it was due to your belief that all "specialists" outside North America a less than able.
So I made mention of RCM's history, Roger Clark Motorsport, Roger Albert Clark Rally, which was renamed RAC Rally. Do you understand the connection?
Do you understand how long that particular UK "specialist" has been trading and developing cars for motorsport and modifying them for high performance road use?
I assume you think Cosworth are an American firm aswell? Rather than one that started up in a shed in London in the late fifties/early sixties.
Is there any reason why you chose to be so obtuse? Rather than simply admit that UK Subaru specialists are more than a few years ahead in their life of Turbo Subaru development and therefore they may have learned a trick or two.
And I would personally consider a 2.2 Boxer lump running mauls pistons and I would suspect copious boost to be a prime candidate for the best oil going.
One other small details I think a few have misunderstood the OP's temperature requirements.
I read it as -15oC to 25 oC which is a fair temperature range, very similar to what you get in large swathes of Western Europe
I don't know why I am trying to explain this to somebody who is certainly a fan of thin oil, and there is nothing wrong with that. Especially as my '04 WRX was almost certainly ran on 5w30 from the factory, however as I specced Mobil 1 at the 1000 mile service I suspect that it may have been 0w40 from then on.
Now I would also say that the OP will almost certainly have no issues running 0w40 or 5w30 to the shops with low boost and low revs.
Would that continue on the track or under more aggressive usage?
No, it wouldn't. The engine will suffer.
So the general consensus in the UK is to spec oil to cover all scenarios.
I suspect ScoobyClinic are more comfortable speccing 10w50 for all year use and to be honest they have. Much smaller R&D budget, if in fact they have any. Now RCM have certainly invested large amounts of cash into R&D and have come up with 15w50 for year round use.
Note it is not common to use different oils in summer and winter in the UK.
And on the subject of cold starts, the engine internals will not be wiped clean of the oil left when previously ran.
It follows that if you are running a high quality full synthetic 15w50 or 10w50 than the oil left to cling to the moving parts and costing all those nooks and crannies will be either 15w or 10w and will therefore provide protection whilst the sump oil is circulated by the pump, correct?
And due to the relative difference in cold viscosity and intact hot viscosity surely the thicker the oil the more will remain inside the engine waiting to protect on start-up? At least that is the way I see it.
But since my knowledge on this is limited I go with a specialists opinion.
