Engineer’s Angle: Keep on top of boat’s bloodwork to save engine’s life

Aug 15, 2018 by JD Anson

Engineer’s Angle: by JD Anson

For days on end, machinery on board runs nonstop. Myriad parts are constantly rubbing together under incredible pressure, separated only by a film of oil a few thousandths of an inch thick. That oil is the lifeblood of the boat.

Just as a doctor can use a blood sample to check a person’s health, a sample of oil offers insight into the condition of an engine. And like blood, oil performs several important tasks simultaneously. Not only is it there to lubricate and prevent wear and friction, but it also is cooling and cleaning the insides of the machine, be it a small pump or a many-thousand horsepower main engine.

Oil sampling is easy to do, but must be done correctly to be of value. A written procedure must be established and followed. If your boat has no established procedure, making one right away can begin the trend for later analysis. The longer the history, and thus more data, the better. Do not wait for symptoms to arise before beginning to sample the oil.  If you are noticing a problem without using samples, it is probably too late.

There is no one-size-fits-all procedure. It is more important that whatever method is used is followed to the letter. Failure to do so can cause wildly varying results, and these variations will make it impossible to monitor changes in conditions over time. Testing intervals should be established based on hours of use or fixed period of time. If the manufacturer has not specified an interval, at a minimum the samples should be taken at each oil change.

When taking a sample, remember that cold oil has fewer suspended particles than warm, so sampling must be done after the machine has reached operating temperature for at least 15  minutes. Each sampling container kit comes with a small tube to draw oil from the dipstick tube using a hand vacuum pump. The tube should be inserted into the dipstick tube until it touches the bottom, then withdrawn a bit to avoid sucking particles off the bottom of the oil pan, which would skew the results.

If provided, a sample may be taken from a sampling draincock. When doing so, let the oil run for several seconds before sampling to flush the passageway inside. Use protective gloves and safety glasses to prevent burns from hot oil, and ensure that all sampling equipment is clean and free of contamination.

Once the sample is received by the laboratory for analysis, it will be heated to a specific temperature while mixing the sample thoroughly. It is then tested for properties such as viscosity and acid neutralization, which will indicate the level of breakdown in the oil. Viscosity is related to the oils ability to lubricate, while acid neutralization shows the condition of the oil as it oxidizes from age and use. To establish a good baseline for comparison, it is recommended that a sample of the oil directly from the drum be tested as well.

The oil is also tested for wear metals and contamination. Each type of internal part is made of specific materials. By using emmisive spectography, the lab can measure amounts and types of metals suspended in the oil. Rising levels of particular metals can be early indicators of damage occurring before it reaches catastrophic levels.

For instance, high levels of copper (Cu) and tin (Sn) can indicate wear on valvetrain components, bearings and bushings while chrome (Cr) can point to wear of rings and exhaust valves. Contaminants can include water, fuel or antifreeze and give advance warning of internal leaks. Dirt and salts can cause wear and corrosion.

A report is issued to the vessel after testing, but without a history of previous samples done according to the same procedure, trends can be impossible to spot. This is why the written procedure must be followed each time to give comparable results. Each sampling kit is only a few dollars, and well worth the expense if it saves an engine.

File the reports chronologically in a binder, one section per machine. Graphing the results on a simple spreadsheet can visually cue one into changes better than a bunch of numbers. Plus, it will give you something to do on long passages.  Because, seriously, how many episodes of Below Deck can you watch?

JD Anson has more than 20 years of experience as a chief engineer on megayachts. He is currently project manager at Fine Line Marine Electric ( in Fort Lauderdale. Comments are welcome below.