What Oil Says About Your Boat’s Health

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 without oil. 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.

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 boat’s oil in the fall.

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. Vessel Vanguard provides various types of oil and fluid analysis services. Oil and fluids are analyzed, digitally captured, and automatically integrated into the Vessel Vanguard app where the results remain available and can be accessed at any time.

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.

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

Samples need to be taken with the engine at normal operating temperature. Any particulates contained in the oil sink to the bottom of the 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 it’s condition and, by definition, the surfaces that it lubricates.

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.

Insert the other end of the plastic tube into the sample pump, and then screw on the plastic collection bottle.

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 collection container from the pump before immediately screwing on the cap. Be careful not to spill any.

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.)

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.

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.

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 is heated until it starts to produce a vapor that can be ignited. If it is contaminated with gasoline or diesel has a lower flash point 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.

Common Elements Found In Oil Samples

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

How Much Does Testing Cost?

Presently the lab cost for professionally conducted oil sample analysis is approximately $275 for 10 kits. 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 pro-testing.


Polaris Laboratories: Vessel Vanguard’s trusted partner.

Mark Corke

Contributing Editor, BoatUS Magazine

About Vessel Vanguard

Vessel Vanguard is a leading marine safety and maintenance management software provider dedicated to revolutionizing the maritime industry. With a commitment to innovation and excellence, Vessel Vanguard delivers cutting-edge solutions to streamline operations and enhance vessel performance and safety.

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