Diesel engine oil analysis
An engine oil analysis can help you identify minor problems before they become major problems. Finding problems early maximizes engine reliability and efficiency, which in turn extends engine life. You may also be able to extend oil drain intervals, thus saving money.
If you buy a used boat and choose not to get a full engine survey, do yourself a favor and at least get the transmission and engine oil analyzed. A typical oil analysis runs about $20, which is cheap insurance.
How to take an oil sample
When taking your oil sample, make sure your engine and/or transmission is near normal operating temperature. Take your sample from the center of the sump to ensure that it’s representative of all the engine oil. In other words, don’t take the oil from the top or bottom. Finally, don’t allow your samples to be contaminated with dirt or oil from a previous sample.
Oil analysis is all about change. It's essential to have a new lube reference with which to compare your used oil analysis. You will be looking for changes in oil properties, including contamination, additive depletion rates and viscosity fluctuations.
What tests look for
Typical oil analysis testing looks for wear metals, such as iron, chromium, aluminum, nickel, copper, lead, tin, vanadium and silver. Depending on which metal shows up in your analysis, you may be able to determine what part of the engine is wearing out. For example, high levels of iron could signify that your gears, crankshaft or camshaft is wearing. High aluminum levels could indicate piston scuffing. If your analysis comes back with high wear metals flagged, your mechanic may be able to pinpoint the cause early.
Oil sample analysis also measures contaminant metals, such as silicon, sodium or potassium. High silicon levels might indicate a dirty engine environment because everyday dirt is a major source of silicon. High sodium levels might indicate salt-water contamination. You will need to research the causes of elevated levels of contaminant metals.
Additive metals also show up in oil analysis. These metals are added to oil after refining to improve various properties such as detergent dispersant or anti-wear. One important additive gives oil the ability to neutralize acids created in the engine during combustion.
Elemental metals analysis, discussed earlier, detects metals in used oil due to wear, contamination or additives. This test can determine the type and severity of wear within an engine or transmission.
The base number test measures the oil’s alkaline reserve or ability to neutralize acids. Acids are a result of combustion by-products and oxidation. Excessive acids increase engine component wear.
The oxidation test measures the breakdown of oil due to age and operating conditions. Oxidation prevents additives from performing properly, promotes the formation of acids and increases viscosity.
Fuel dilution measures the amount of raw, unburned fuel that ends up in the crankcase. Fuel dilution lowers oil’s viscosity and flash point, creating friction and related wear almost immediately by reducing film strength.
Another test measures water in the oil. Needless to say, there should never be water in our oil.
The viscosity test measures a lubricant's resistance to flow (fluid thickness) at a certain temperature. Depending upon lube grade, viscosity is measured at 40 or 100 degrees Celsius. Viscosity is considered oil’s most important physical property.
Finally, a soot test measures and reports soot as percent of volume. Indicating reduced combustion efficiency, soot can be caused by over-fueling, air restrictions, blow-by or excessive exhaust backpressure.
Reading the numbers
As mentioned earlier, oil analysis is all about change, which makes it difficult to tell what a "good" or "bad" number is. Readings will differ based on the oil or the engine or transmission. Your mechanic should be able to provide some guidance.–Gary Ball
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