Here FYI are the results from using Mobil 1 5W-40 synthetic oil in my USMY 02 WRX. The car has 35K miles on it, and the oil was left in use for 5,800 miles, since I'm in no mood to be changing oil every 3,000 miles in the 21st century - no reason for that IMO, and the data proves it for this particular motor and this particular oil with my use patterns.
I am a bit anal about proper maintenance, so I wanted an decent motor oil that was API SL certified and would protect the motor as well as possible with a reasonable oil change interval - I set my mind on 5,000 miles.
Mobil 1 5W-40 is labeled "Truck and SUV" as a lame marketing ploy, but turns out it's a great oil (even with no Mo in it!). It's the bottle with the yellow cap.
Here's the data:
TBN = 3.5
(All elements below in ppm):
The explanation for each item from the laboratory:
Aluminum: Pistons, bearings, cases (heads & blocks).
Chromium: Rings, a trace element in steel.
Iron: Cylinders, rotating shafts, the valve train, and any steel part sharing the oil.
Copper: Brass or bronze parts, copper bushings, bearings, oil coolers, also an additive in some gasoline engine oils.
Tin: Bearings, bronze parts, piston coatings.
Molybdenum: Anti-wear additive, some types of rings.
Nickel: Trace element in steel.
Manganese: Trace element, additive in gasoline.
Silver: Trace element.
Titanium: Trace element.
Potassium: Antifreeze inhibitor, additive in some oil types.
Boron:_ Detergent/dispersant additive, antifreeze inhibitors.
Silicon: Airborne dirt, sealers, gaskets, antifreeze inhibitors.
Sodium: Antifreeze inhibitors, additive in some gasoline engine oils.
Calcium: Detergent/dispersant additive.
Magnesium: Detergent/dispersant additive.
Phosphorus: Anti-wear additive.
Zinc: Anti-wear additive.
Barium: Detergent/dispersant additive.
Water and fuel dilution are indicative of short trips and idling; antifreeze means just what it implies - antifreeze in the oil therefore a failed head gasket or other bad news.
So far, so good then it seems. Since I can go 5,800 miles on the oil, changing it every 5,000 ought to be very safe and yield good results.
I'm happy with the data.