Getting your engine, transmission, or lower unit oil tested can yield valuable
information ... if you know what to look for.

Think of the oil in your engine like the blood in your body: You cannot survive
without blood, and neither can your boat’s engine. When you get a checkup, your
doctor often orders a blood test to check your overall health. The same can be done
for your engine.
According to BoatU.S. oil samples are best taken at regular intervals each year.
These, for example, can either be drawn every 50 hours or, if the boat is only used
lightly, just before winter layup, which is what I do. Doing an oil analysis yields a
snapshot of one particular moment. Although that can provide enlightening
information, regular sampling is far more beneficial as it allows the boat owner or
mechanic to monitor and track a specific engine during its lifetime. The first sample
acts as a baseline to which you can compare future samples, giving you a good idea
of what’s going on in your engine or drive.
How to take an oil sample
Taking an oil sample is pretty straightforward. The first step is to purchase an oil
sample kit from a reputable supplier, usually the same place that will be analyzing
the results.
You’ll need just two items to take an oil sample: a small plastic container to hold the
oil and a special hand pump for drawing the oil up through the dipstick hole. There
are usually no instructions that come with the kit, so here’s how to go about it.

1. Oil samples need to be taken with the engine at normal operating
temperature. Any particulates contained in the oil sink to the bottom of the
oil pan of a cold engine, but warm oil that has circulated throughout the engine will hold these particles in suspension giving a more accurate reading
of the oil’s condition and, by definition, the surfaces that it lubricates.
2. Shut down the engine once it has reached normal operating temperature and
remove the dipstick. Insert the plastic tube that comes with the sample kit
into the dipstick tube until it reaches the bottom of the oil pan. Then pull it
back an inch or two so you are only withdrawing oil, not any gunk stuck to
the bottom of the pan.
3. Insert the other end of the plastic tube into the oil sample pump, and then
screw on the plastic collection bottle.
4. Operate the pump with slow, deliberate strokes to suck up oil from the
engine. Keep pumping until the container is almost full. Place some rags
under the pump to collect any drips. Once full, unscrew the oil collection
container from the pump before immediately screwing on the cap. Be careful
not to spill oil.
5. Remove the plastic tube from the pump, and after allowing any remaining oil
to drain back into the engine, remove it from the dipstick hole and discard
the tube. (Each tube is used only once to avoid cross-contamination.)
6. Fill out the adhesive label as thoroughly as possible with engine hours, serial
number, and other requested information, and stick it onto the container. It’s
imperative to label each container immediately after taking the sample. If
drawing multiple samples, it’s all too easy to get them mixed up.
7. Once the samples have been taken and labeled, place them in the supplied
envelope, box, or tube and mail them to the lab. You can expect to get the
results via email within 72 hours.

TIP
Be consistent when taking oil samples so you have a comparison from year to year.
A good time to do it is when changing the oil in the fall.

Testing is high tech

Once oil arrives at the lab, it is divided up into smaller samples for different
individual tests. One of these is the flashpoint test. A small sample of oil is heated
until it starts to produce a vapor that can be ignited. Oil contaminated with gasoline
or diesel has a lower flashpoint than an uncontaminated sample, which is valuable
information.
Oil is also checked for metal elements by vaporizing the sample and sending it
through a spectrophotometer, a machine that measures the amount of light that
passes at different wavelengths. The results help the lab determine the amount of
each metal present in the sample in parts per million (ppm). Based on stored data,
the lab can interpolate those results and what they may mean for each tested
example. For example, excessive amounts of a certain metal could indicate that
some component in the engine is experiencing wear, typically bearings or some
other part.

Here are some of the most common trace elements found in oil samples and some of
their likely sources:Cu – copper from oil coolers and bushings
Fe – iron/steel from worn bearings or journals
Al – aluminum from pistons
Pb – lead from wear in the main crankshaft bearings
Na – sodium, most likely caused by antifreeze from the cooling system finding its
way through a crack or pinhole and diluting the oil
Ni – nickel from crankshafts, valves, and camshafts
P – phosphorous typically comes from antiwear additives in the oil
Cr – chromium from cylinder liners and piston rings
Fuel – often caused by blow-by from the combustion chamber, which dilutes oil and
makes it less effective

TIP
Every brand and weight of oil has unique characteristics. Only use oil recommended
by the engine manufacturer. Using different brands or viscosities may skew analysis
results.

How much does it cost?
Presently the lab cost for professionally conducted oil sample analysis is about $30.
Although there are DIY sample kits where drops of oil are placed on special sample
cards and then compared to a supplied colored reference chart, these are a poor
substitute for professional testing.

Mark Corke is associate editor of BoatU.S. magazine and is also a SAMS (Society of Accredited Marine Surveyors) surveyor.