tditom said:
OK, so basically these readings are "in the noise".
At what point is Fe level considered at the upper acceptable limit?
Tom,
Test results can vary +/- 10% when the same sample is tested in the same lab by two different techs - and can vary up to +/- 20% when tested in two different labs. This means that for an average iron production of 2ppm, the same sample will read between 1.8 and 2.2 ppm for a 10% variation, and 1.6 and 2.4 ppm for a 20%. This is on the same sample. 3ppm is in no way considered abnormal and should not trigger an oil change.
Another point is that limits are set for the manufacturer's standard oil change interval. Higher levels are normal for extended drain intervals. Generating iron at 2ppm per 10,000 miles will mean that one should expect to see 4ppm for a 20,000 mile OCI and 6ppm for a 30,000 mile OCI. If, for example, the iron level becomes abnormal at 40ppm for a 10K change, that limit raises to 60ppm at 15K, and 80ppm at 20K miles.
It is normal for wear metal production to be high at break-in, then vary for the life of the engine. Numbers will rise again as the engine breaks down.
Oil analysis is a trend device - the first thing that should happen if one report shows odd numbers (that are below condemnation limits) is to note the changes, keep driving, then pull another sample at the next interval.
VW should set acceptable limits. In the absence of VW guidelines, general limits are used. These are the numbers labs use for automotive diesel engines:
Element Normal Abnormal Excessive
Iron 10-40 100 300
Chrome 1-8 12 15
Lead 15 30 75
Copper 3-15 50 150
Tin 15 20 30
Aluminum 10 15 25
Nickel 5 10 15
Silver 3 10 30
Silicon/Silica 15 25 30 (over new oil baseline)
Sodium 25 100 150
Physical property changes are normally looked for first. Most people want to change the oil before the additive package degrades enough for you to see engine damage.
As a rule, these are normal, abnormal, and excessive signs of physical degradation and contamination:
Normal: glycol 0, water < .05%, fuel dilution < 1%, viscosity in grade, solids < 1.5%, soot < 2%, oxidation/nitration less than 30% (petroleum) and 50% (synthetic), TBN greater than 2 or greater than 50% of new
Abnormal: Glycol trace, water .05%, fuel dilution 2%, viscosity up or down one SAE grade, Solids 2%, Soot 4%
Excessive: trace of glycol, >.1% water, >5% fuel dilution, viscosity up or down one grade, >4% solids, >6% soot, oxidation & nitration greater than 50%, TBN at/below 2 or below 50% of new
I hope that helps,
Andy