Engine oil lab analysis – is it worth it?
Engine oils can be examined for condition by spectroscopic laboratory analysis. It is often likened to a human blood test. In many ways it is a good analogy in that it flows round collecting residues created by the functions of various components. The analysis can test for various metals and minerals, some are intentional and some accidental;
Carbon or soot from combustion process, high levels are from poor combustion typical of a powerful engine that has spent most of it’s life idling in speed limited rivers.
Iron results from general engine wear, piston rings, bores, cams, crankshaft etc. All engines will gradually shed wear metals into the oil.
Nickel is alloy used in steel making as well as bronze. This will appear when Iron and bronze components wear. It is also used to plate components as a base for chromium plating.
Chromium comes only from plated components such as rings or bores, If an engine doesn’t have plated bores then high chromium levels means significant wear elsewhere.
Aluminium is mainly used for pistons so wear comes from piston skirts. Aluminium is also used as a bonding layer in engine bearings and can be a component of white metal bearings.
Copper is also used in engine bearings as a backing shell. It can also be copper oxide stripped from pipework in oil cooler cores
Lead is a principal element of most white metal bearing surfaces. This will usually be seen in similar quantities to tin
Tin and Zinc nearly all engines use white metal for big end and main bearing shells. White metal is made from various alloys of lead tin and zinc so all these metals will appear in various proportions.
Silicon is a generally atmospheric dust so intake air filtration should be looked. However there are some other sources such as anti foam additives for diesel fuel and gasket sealants
Sodium is a prime element in antifreeze so high levels usually originate from engine coolant leaking through head gaskets failure.
Boron is used as a corrosion inhibitor in antifreeze so can be seen in conjunction with sodium, however it is also used as a high pressure additive in engine oils.
Vanadium is used in surface coatings for hardened steel components such as turbo impeller blades and valves.
Phosphorus is a common component is bronze bearing bushes used for jack shafts, cam shafts and valve guides.
So the lesson from all this is that the real skill in the ‘analysis’ is not in the separation of the various elements within the oils, it is in translating those levels into some kind of identification of the problems that they are showing up. For instance, high levels of Boron can occur naturally as a oil additive, but seen with also high levels of Sodium can mean head gasket failure. Copper can be easily explained in an engine with an oil cooler but, if no cooler is fitted, then the source is almost certainly bearing wear.
The more information that there is about the engine and the oils will help greatly in the analysis. The grade of oil, type of oil etc is invaluable. The other issue which often skews the findings is engine hours since that last change. In a pre-purchase survey an owner will often underestimate the hours to give the impression that the engine has been maintained to the highest standards. Here he is shooting himself in the foot as the more hours the lower the rate of wear. This is particularly important in the levels of Iron because all engines will shed iron almost continually at a microscopic rate.
So oil analysis is not an exact science and the best that you will get is an opinion based on various findings. Here the analogy with a blood test is accurate because doctors will tell you that blood tests cannot detect diseases on their own. It is a tool to be used in conjunction with other symptoms. They will also tell you that there are many other factors that can give abnormal readings. The big difference with a blood test is that humans don’t have a total transfusion every year.
Doctors will also tell you that the most accurate tests are those made on a regular basis. These are no longer spot tests vulnerable to misdiagnosis for the reasons given above. This trend analysis gives a whole new insight observing progressive change in metals and contaminants. It is an easy process to send off a sample from every oil change, yet in many years of surveying I have yet to see a vessels maintenance log with annual oil analyses.
However, it is also a matter of economics. The cost of an engine oil analysis at £60 to £100 represents a fraction of 1% of the replacement cost of a powerful marine diesel engine. Most boat owners think marine insurance policies at about 1% are cheap when compared to motor insurance, so thinking about it as a cheap annual insurance policy makes a lot of sense.