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What Your 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.

Closeup of engine component for oil

Oil samples can tell you a lot about the health of your engine. Taking samples each fall allowes you to track your engine's condition. | Photo Credit: Mark Corke

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.

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 oil recommended by the engine manufacturer. Using different brands or viscosities may skew analysis results.

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.

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

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.

Oil Chart

This is what a typical results sheet looks like. There's a legend to explain the abbreviations, but note the green box at the top that says "no action required." If this box is red as in the lower example, it's an indicator that something is wrong and you should pay attention to the lab technician's notes in the report.

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 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.

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

How Much Does Oil Testing 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 pro testing.

Resources

Blackstone Labs: Supplies, testing kits, and vacuum pumps

Mark Corke

A marine surveyor, and holder of RYA Yachtmaster Ocean certification, Mark has built five boats himself — power and sail. He was senior editor of Sail magazine's hands-on "Boatworks" publication, worked for the BBC, written four DIY books, skippered two round-the-world yachts, and holds the Guinness World Record for the fastest there-and-back crossing of the English Channel, in a kayak! He and his wife have a Grand Banks 32.