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RE: 15w-50w inferior

<<< Well BMW can recommend 5w-30w Mobil 1 if they want, but I spent the
weekend 
changing engs. on a rig that got it's 3rd eng at 124,000 because of the
label
on the oil fill cap that specifies 5w-30w. Anything I own that holds oil
gets
15w-50w Mobil 1, period. Many manufacturers subscribed to the theory for
awhile
that running light oil to meet cafe standards and replacing rod and main
bearings as a maintenance item at 25-35k mi. was ok. Not in my book. >>>

I understand your concern about running excessively low viscosity oils
in a high performance engine, but you must remember that synthetic oils
are designed to operate over wider range of temp. ranges than
conventional
oils. Hence the fewer variations available.  Results from my oil analysis
show that the 10W-30 and the 15W-50 are similar in viscosity at 100 deg.
Celsius. Here is the data from the analysis.

 VIS @ 100 deg.
11.74     Valvoline 15W-40 oil run for 3000 miles
16.80    Mobil 1 15W-50 oil run for  4000 miles
15.39    Mobil 1 10W-30 oil run for 5000 miles

The chart for reference is as follows:
Oil Grade       Min         Max
10W	      4.1
20                    5.6          9.29
30                    9.3        12.49
40                   12.5       16.29
50                   16.30     21.89

As you can see both, Mobil 1 10W-30 falls into
the 40 grade category while the 15W-50 falls
into the 50 grade category.  Thus you could 
say the 10W-30 is acting like a 10W-40 oil.
		

Prakash Maggan
'92 DINAN 750iL
Maggan@domain.elided
http://ourworld.compuserve.com/homepages/PrakashMaggan