Understanding Fuel Contaminants
By Tom Bock
As I promised I will answer questions that are sent to: firstname.lastname@example.org. Here are a few of the questions I received in the past quarter.
1) My iron has increased on my last sample from 45 to 80; do I need to make any repairs to engine?
This is a common question when it comes to wear metals. The answer needs additional data to properly evaluate the increase in wear whether it is iron, copper, lead, aluminum, tin, chromium or nickel. How many miles are on the engine as engines constantly wear at different rates over their lifetime. New or rebuilt engines have a break-in period where the metal parts seat and set the tolerances usually up to 100K miles. From 100K to 500 or 600K the wear rate will slow down then pick up again as engine parts being to fatigue. How many miles are on the oil as wear rates are determined by parts per million per 1000 miles. Engines that use devices to extend oil drains will have some accumulation of wear metals over time. The wear metals are not chunks of metal but similar to the iron you have in your blood, very smaller particles. An engine with iron of 80 PPM at 10K on oil may require some repair but if 100K on oil the wear is well below an abnormal wear pattern. This is the reason labs ask for the miles on oil and engine since it was new or rebuilt.
2) What is a normal wear level for my engine?
Manufacturers do not publish their wear metal rates for obvious reasons but over time oil analysis labs have produced charts that help them to evaluate engine wear. For example a Detroit Diesel engine with iron wear of up to 74 ppm and a lead wear of up to 24 ppm, would be classified as normal at 300K miles. Keep in mind that engine age has a bearing on the results but the labs charts are good resources for comparison. The wear pattern for your engine is the determining factor that should be evaluated before spending $$$$ to inspect and determine if repairs are necessary.
3) Are there any combinations of wear metals or contaminants that can help to identify an engine defect?
While it is very difficult to pinpoint a defective part the oil sample results can be very helpful to determine the engine components that should be inspected, For example if sample has high sodium and potassium levels chances are there is a leak in the coolant system causing antifreeze to enter oil. Copper, sodium and potassium would indicate a defective EGR or Oil Cooler. Etc. Potassium without sodium usually indicates a recent repair whereby the parts were not cleaned of the potassium based protective coating. Sodium (salt) without potassium is an environmental contaminant road salt for example. The combination of aluminum and fuel is most likely a fuel pump; fuel without aluminum would be an injector or fuel line issue. Increased soot and silicon (sand) usually indicates a clogged air filter or incorrect fuel to air ratio causing unburned fuel.
4) What causes increases and decreases in viscosity?
Viscosity describes a fluid's internal resistance to flow and may be thought of as a measure of fluid friction. The viscosity can be affected by heat, cold, additives, contaminants (fuel, water, antifreeze, soot, solids). The modern multi-grade oils are formulated to flow at a constant rate when temperatures are within the acceptable range. However severely overheating the oil will cause oil to thicken due to stresses placed on molecules. The analysis labs test the oils at 100 degrees C to ensure the higher temperatures produced in engine will have proper flow rate. Using additives will have an effect on the oil and usually they increase the viscosity which reduces the flow rate. Fuel and water will lower viscosity and antifreeze , soot and solids will increase the viscosity. The labs will usually recommend changing oil if viscosity goes up or down one grade level when utilizing extended drain products.
5) Why did my oil usage increase dramatically when I changed from standard oil to synthetic oil?
The oil film for standard oil is thicker than for the same grade level of synthetic oil, so the parts have been fitted to the tolerances created between the rings and cylinders riding on the oil film for example. The new synthetic oil being thinner will cause oil to pass through the gaps and burn until the parts become accustom to the new tolerance. This varies with age of engine but usually will subside after 5k to 10K miles.
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