Hi,
Slickfisher - you said;
"Acutally it could be a big deal- climbing the elevations where he lives the turbo can generate a lot of heat."
and;
"Funny, now Mobile has a big long drain interval campaign with talk how well their oils do over the long term. I hope it's true, because a lot of people running small displacement turbocharged engines in realitively heavy cars will pay a price if it all hype."
In real terms a Manufacturer's oil Approval test protocols can go way beyond a simple HTHS test for a variety of reasons. These are usually tailored for its engine familie's metallurgy, expected operating oil temperatures and application/use. This is the case with the extended HTHS testing carried out by Porsche - all of their Listed oils have passed this and their extended 100C viscosity and special anti-foaming test and other protocols too. No xxW-30 oils of any brand are currently Approved!
Both Castrol's "BC" 5w-40 and Mobil 1 0w-40 are Approved and Listed by Porsche.
M1 0w-40 is their factory fill and a 0w-40 lubricant is the mandatory service fill for their ultra high performance twin turbo Cayenne V8 and etc.
I was an initial user of GC 0w-30 when it was first introduced nearly 10 years ago (and as many on BITOG know, Pscholte has bestowed "Honorary Elf" status on me)
IMHO and in this specific application I would pay the extra money and use a 0w-40 oil!
I use M1 0w-40 in my supercharged Benz over Delvac 1 5w-40 and I live in the Tropics where the ambient is often way beyond 38C (100F)
1bar - IMHO I would expect that the HTHS of the Porsche Approved & Listed oils (0w-40, 5w-40) to remain higher that a non Approved (or no longer Listed) xxw-30 lubricant during normal most vehicle applications and over prescribed OPCIs
Also remember that German cars are put together to run fast and long on their Autobahns and through high mountains in temperatures from below -30C to 40C+ as well as normal city/urban use
Doug