David
This is the full thread from which you are quoting :
http://bbs.scoobynet.com/general-technical-10/608314-oil-you-get-what-you-pay.html
Your grasp of oil technology is simply quoting what another
Engineer has quoted but this is more in context on forced induction engines in the main
where lubrication duties have vastly greater temp / pressure criteria than that
found on a large n/a engine with a very efficient engine oil cooler fitted as std.
Thats why I use Mobil one 15w/50 synthetic on my Skyline.
It's duty cycling means constant exposure to several hundred degrees Celcius within the
intermediate housing of the turbocharger.
In extremes, the Turbocharger can reach 1000 Deg C
All that with high pressure oil feed to the turbine shaft bearings, you need
the best chemical formulation when bulk oil temps exceed 140 Deg C
Its resistance to breaking down under these much more extreme conditions make
it worth paying for.
With the added security that its an oil that is proven to work in a forced induction vehicle using the
correct viscosity.
May I ask what the highest bulk oil temperature you have measured on any of the
E34 M5 's you have owned ?
I would suggest that whilst viscosity is not the only issue , in context of the application for S38
where oil bulk oil temp rarely, if ever exceeds 110C or around 230F, the engines do not need anything
remotely exotic.
The "Planet oils" I use are rated far beyond this temperature.
The S38 application :
The vehicle in B36 guise was a world vehicle in 1988.
In B38 circa 1991,it was a mainly European offering due to pass-by noise & emissions
In all cases, it was tested on Cold crank test, Autobahn signoff, Altitude soak @ Grossglockner &
as you have quoted, many thousands of Kms at the Nordschliefe.
All this with Mineral oils @ an average of 6k mile service intervals.
So then, whats changed please ?
Oilman has recommended 5w/40 for colder climates & winter use where more
efficient cold crank can utilise the thinner when cold oil.
He has just been approved as member & I am sure he will be happy to answer
specifics.
David
I have seen no actual failure of the valvetrain parts in this application...yet.
What I can say without doubt is the that all the cars I have seen
running 10w/60 have bad pitting of camshafts.
No exceptions.
These engines as exmained have as little as 90k miles on them.
From past experience, it has been documented that when pitting gets bad enough,]
the surface hardening of the cam no longer has
the integrity.
The compression, shear & turning forces concentrate on the damaged areas.
These areas being softer are more likely to fracture over time with
micro-cracking emanating from the damaged areas.
When a camshaft lobe disintegrates, its usually fatal for the engine.
No big mystery.
Same with crankshaft bearing shells in that once you are through the hardened land,
then,wear through the soft shell & potential brg shell being spun out by the crank, a likely conclusion.
The 10w/60 oil you lent me was drained the next day as you know.
Thankyou.
My own engine has no pitting or visible damage of any kind @ 180 plus k miles.
All run on 10w or 15w /40 "Planet oil" for the last 8 years.
A highly stressed ,fragile, about to go bang 3.8zzzzz
Wow, who would have thought it.