In Reply to: Oil Analysis results posted by Jack on September 21, 1999 at 08:06:52:
: I had my oil analized last week and just got the results back.
: 1999 E46 328i 28,000 miles on the odometer
: 11,000 miles since last oil change with BMW synthetic 5W40
: (approx 50/50 highway/city)
: The reports states that the oil still falls within the spec'ed viscosity range (5W40)
: no trace of fuel, water, or antifreeze in oil.
: and traces of metals (aluminum, iron, copper and about 4 other types of metal) were all virtually non-existant.
: traces of silica (dirt) are also very minimal. (using K&N air filter) (there was a side note that said air filter is
: working properly)
: The conclusion of the report was that the oil is suitable for continued use and engine is in excellent condition.
: I think BMW engineers know what they're doing, and it'll be safe to go 15k to 18k before changing the oil.
: When it hits 18k, I'll send the oil in to be analized again and will post the results.
Typically we shouldn't find dirt or metal particles in the oil except in the oil filter because that's what the oil filter is for. While test can analysis the viscosity, it cannot analysis lubrication properties, especially the effectiveness of the detergent level after 10,000 miles whether it can still suspend contaminates instead of gumming up the internals. Engine performance cannot be guaged until years down the road. This is just my own opinion, no flames please. Also if there's minute traces of silica (dirt) has nothing to do with oil. It's the air filter that's passing it through into the engine. I'd say, the air filter is letting thru quite a substantial amount of dirt to be shown in the oil. Bear in mind that dirt in the oil had to pass thru the oil filter too. That's another reason why I stay away from K&N filter.
The strict rule of 15K oil change cannot be applied to different style of driving. A guy who always hotrods, inevitably let's quite a bit of fuel by-products thru the piston/cylinder and ended up in the oil as compared to someone who always drives convervatively.
Just my 2 cts on the pro and con of long term oil change.