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The Importance Of Oil Sampling

Oil Sampling

This is a case study of how oil sample analysis can reduce the risk of poor engine performance or catastrophic failure.

Today’s diesel engines are designed and built to run trouble free for thousands of hours before needing major service or rebuilding. Follow the manufacturer’s maintenance schedule, make sure your fuel is clean and free of water, and you can count on your engine to run as if your life depended on it.

Everyday boating can put you in a precarious position—running a rough inlet or entering an anchorage between coral reefs, for instance—and knowing you’ve done everything possible to ensure that your engine won’t falter will allow you to focus on the immediate task of safely piloting your boat. Even if you’re rarely exposed to such conditions, your diesel engine is a major investment that’s worthy of extra special care. And, of course, if you own a single-engine powerboat like I do, your safety very much depends on your engine’s good health.

Much like having your cholesterol level checked, an oil sample analysis can tell you what’s going on inside your engine. Some boat owners refuse to have their engine oil analyzed because they “just don’t want to know that much.” If their engine seems to be running OK, that’s all they need to know. But with the cost of an oil analysis being only around $30, Ben Franklin’s “an ounce of prevention is worth a pound of cure” comes to mind.

Personal experience with my single-engine Thomas Point 43 made me a believer in the concept of oil sample analysis. Powered by a 435hp Caterpillar 3208, Sawdust has safely taken my family on a 6,000-mile Great Loop cruise, on numerous trips up and down the East Coast from Maine to Florida, and to the Bahamas. We have made offshore runs well beyond the sight of land, sometimes as far as 100 miles from shore. When I had the boat built in 2000, I specified the Cat 3208 because I understood it to be a well-proven, bulletproof engine. I knew of watermen who had run their 3208 engines for more than 8,000 hours before needing any major overhaul work.

After owning the boat for two years and putting 660 hours on the engine, I decided to conduct the first oil sample analysis at the suggestion of a mechanic in Fairhope, Alabama. We had arrived in Fairhope after traveling down the rivers and waterways from Lake Michigan, and while the engine was running flawlessly, I began to make oil sampling a routine procedure each time I changed the engine oil, which I normally did every 125–150 hours. We would soon be crossing the Gulf Stream and heading down to the Exumas, and I wanted extra assurance that our engine was in good health.


The actual sampling procedure is simple. While many engine dealers, including Caterpillar, provide oil sample analysis, there also are independent labs—such as Blackstone Laboratories ( and POLARIS Laboratories (—that offer the service for any brand of engine. Many experts recommend having oil analyzed by a lab that is independent of the engine manufacturer.

The first step is to take a 4-ounce sample of spent oil and put it in a plastic bottle supplied by the lab. Next, the sample is sent to the lab, along with such information as the engine’s make and model, serial number, and total hours of use; hours on the oil sampled; and the brand and type of oil used. It’s important to provide a “clean” sample by letting a quantity of spent oil run out of the discharge hose or oil pan before bottling. (For guidelines on taking oil samples, see; for coolant sampling guidelines, visit

Things that the lab will be looking at include the metal wear rate; the oil’s chemical condition; and coolant, water, and fuel contamination. It normally takes about a week for the results to be sent back from the lab, although results can be rushed, and most labs will email the results to you. (For more information on the technical details of oil sample analysis, see PMM Nov./Dec. ’07.)

Wear-rate analysis detects and identifies miniscule metal particles caused by component wear or failure. Every engine produces some wear metals, but if the concentration of particles increases between samplings, it usually is a sign of trouble. The acceleration of wear is the key here; you need to establish and analyze trends in the data. While absolute numbers are meaningful, even more important is knowing whether certain conditions are changing. At least three samples are needed to establish and identify a trend, so if you suspect a problem, it’s wise to conduct oil samplings more frequently than your normal oil change schedule dictates.

Typically, the metals that labs look for and quantify include copper, iron, chromium, lead, tin, aluminum, molybdenum, silicon, and sodium. While both the engine manufacturer and independent labs are able to roughly pinpoint probable causes of elevated levels of metal particles, be forewarned that a good amount of guesswork will be used in their analyses and recommendations. Depending on the combination of elevated metallic elements, it may be determined that the source of excessive wear could be the engine’s pistons, rings, valve train, crankshaft, or bearings. As with diagnosing a deadly disease, the only way to tell exactly what’s going on is to open up the patient, which is a very expensive proposition.

An oil chemical analysis is similar to a wear analysis, except that it examines the chemical compounds in the oil. For this analysis, the lab will need to know the brand and type of oil you are using in order to establish a reference. Soot, oxidation, nitration, sulfur, and acid contaminants—all of which can prevent oil from doing its job—will be evaluated. In some cases, it may be beneficial to include a reference sample of new, unused oil for comparison purposes.

Lastly, the oil will be tested for the presence of coolant, water, and fuel. Coolant in your engine’s oil indicates a cooling system leak and will cause oxidation of the oil, leading to plugged oil filters and accelerated wear. Even a small amount of water (0.5 percent or more) in engine oil is problematic.

Water can find its way into the oil by means of condensation or via a leaking oil cooler, gear-driven water pump, or cracked exhaust manifold. It can quickly damage any oil-lubricated surface by creating hot spots that can fracture or scuff metal components. And, of course, the presence of water during periods of non-activity, such as winter layup, will have corrosive consequences.

Fuel is not a good lubricator, and its presence in oil will greatly reduce the oil’s performance. Typical causes of fuel contamination are failed injector pump seals and defective injector nozzles.


My first oil sample analysis report stated that the wear-metal readings were “normal.” When I asked folks at the Caterpillar lab what the levels of each metal should be, they seemed a bit evasive, saying that each engine is different and that the trends are the important thing to watch. So I did as they recommended and sampled my oil during its next change, after the engine had another 117 hours on it, or a total of 771 hours. The second report stated that there were high amounts of copper and sodium, and it recommended that I “monitor the compartment” and resample the oil in 50–100 hours.

With 902 hours on the engine, my next oil analysis report stated that copper and iron levels were high, and it was recommended that I continue to sample the oil to establish a wear trend. At these early stages, it’s difficult for the lab or manufacturer to accurately diagnose problems or recommend a solution, other than to suggest “monitoring the compartment,” which means simply keeping an eye on things. Considering the eventual outcome of my oil sampling protocol, it’s interesting to note that a problem was detected with fewer than 1,000 hours on the engine.

After returning home from a one-year cruise in the summer of 2003, Sawdust’s engine had just over 1,000 hours on it and appeared to be running fine. At 1,089 hours, I had another oil analysis done, and the report that came back stated: “Aluminum appears extremely high. Resample at half the normal interval.” Following Caterpillar’s recommended 1,000-hour maintenance schedule, I also had the aftercooler removed, cleaned, and tested at the Cat dealer’s facility in Baltimore during winter layup.

During the 2004 boating season, we put only 75 hours on the engine, and even though it seemed to be running perfectly, I was concerned by the oil analysis reports. A few calls to my local Cat dealer didn’t help, as I was told to simply “monitor the situation” and to continue sampling the oil. Their diagnosis was that the aluminum could be coming from the pistons or bearings. Before winterizing my engine that year, I had another oil sample analysis done. Again, it revealed that aluminum levels appeared to be extremely high. At this point, the engine had 1,164 hours on it.

The following summer, another sampling yielded the same results: high aluminum content. As a reference, my very first oil analysis had shown the aluminum content to be 4ppm (parts per million), a number that Blackstone Labs considers a “universal average.” By now, this number was ranging between 38ppm and 64ppm, depending on how many hours the oil had on it. I sent one of my filters to my Cat dealer for inspection, but no unusual debris was found in the filter element.

During the 2005 season, I had three oil samples taken and analyzed while putting 180 hours on the engine. One report from the Cat lab stated that the aluminum reading of 24ppm was “normal.” Each report, however, recommended simply “monitoring the compartment.”

Throughout this entire period, my boat’s engine appeared to be running perfectly. When I casually asked other mechanics and owners of Cat 3208s, including workboat captains, for their opinion, the consensus was, “If it’s running OK, stop worrying.”

Over the next three years, I continued to take oil samples, have them analyzed, and to “monitor the situation.” All of the reports indicated high aluminum readings, and although the analyses didn’t show a rapid acceleration in the level of wear metals, the excessive aluminum readings continued to concern me. In 2007, with a total of 1,400 hours on the engine, I again asked the folks at my Cat dealer for advice. They recommended performing a “blowby test” (or crankcase pressure test) to help determine cylinder wear and the condition of the rings. This test measures crankcase blowby—air/gas leaking past the piston rings into the crankcase—during a quickly advanced wide-open throttle and during gradual throttle advances. The results of this test were normal, showing no unusual wear.

During this time, I also had the oil filters cut open, and two tiny, nonferrous metal parts were found in one of the filter elements. My only conclusion was that something was wearing out prematurely but that it still hadn’t adversely affected the engine’s performance.


At the end of the 2008 season, I sent an oil sample to Blackstone Laboratories and received a rather ominous report. I called my Cat dealer, who now advised me that “something was definitely going on” and said that the only way to identify the problem was to pull the engine and tear it down. Since they wouldn’t know what the problem was until they had looked inside the engine, their rough estimate was “not to exceed $35,000.” This number was disheartening, to say the least, as the engine had fewer than 1,600 hours on it and I had followed the book in maintaining it. I had always used Shell’s high-quality Rotella T 15W-40 oil, and I religiously checked my Racor fuel filters for water and soot contamination. In fact, one mechanic jokingly referred to me as “anal” when it came to maintaining my engine.

Although we loved cruising on Sawdust and she continued to perform flawlessly, during the 2009 season, my wife and I began to think about downsizing to a pocket cruiser that we could easily truck to different parts of the country. I knew I was going to have to solve this engine mystery before I put Sawdust on the market. I joined the Boat Diesel online forum ( and learned that owners of older Cat 3208s had problems with condensation collecting in the aftercooler and finding its way back into the engine. Supposedly, my engine had a newer, improved aftercooler.

My next step was to have an independent Cat mechanic perform a borescope inspection of the engine cylinders. Looking inside the four starboard cylinders, the mechanic found that two had slightly corroded walls, a sign that water must have intruded into the cylinders at some point. While not catastrophic news, this was serious and probably had caused the pistons to become scuffed, resulting in the high aluminum readings. We saw enough in those two cylinders not to bother looking at the other side of the block.

I was perplexed at how this could have happened, considering how careful I had been in maintaining Sawdust’s engine. So I started working my way up the corporate ladder at Caterpillar, hoping to get some answers, if not some relief from the repair bills I was facing. After making many calls and talking with Cat reps at various boat shows, the customer support manager for “Global Pleasure Craft, Caterpillar Marine Power Systems” contacted me. He explained the Caterpillar warranty policy to me and referred me back to my local Cat service dealer. I found it ironic that the customer support manager refused to give me his telephone number. I was told that if I wanted to speak with him again, I should send him an email, and that he would reply.

Discouraged by Caterpillar’s response and following the advice of a mechanic who had worked on my engine and who had once been an authorized Cat service technician, I decided to have a mechanic at the yard where Sawdust was built remove the engine and send the block to a well-regarded machine shop in Baltimore to be rebuilt. This was in lieu of buying a Caterpillar remanufactured “short block.” Not only was this a slightly less expensive approach, but the rebuild would have a one-year warranty, compared with Cat’s six-month warranty. Since the yard mechanic had recently pulled a Cat 3208 for another customer, I assumed he knew what he was doing.

The shop machinist showed me the corroded cylinders, as well as the pitted pistons. Based on the condition of the cylinders and pistons, his opinion was that I probably could have run the engine a few hundred more hours before noticing a drop in performance, but he also felt I was wise to take action when I did. He explained that the condition could have deteriorated rapidly, leading to much more serious damage or even catastrophic failure.

The cylinders were bored and sleeves inserted, and all pistons, bearings, lifter assembly components, and injectors were replaced. While this machine work was expertly done, my engine room was in shambles. The two mechanics responsible for removing and reassembling the engine, as well as coordinating the rebuild work at the machine shop, seemed to have forgotten about my job. A full five months passed between the time I brought Sawdust to the yard and when the rebuilt block was returned to the yard. After waiting another two months for them to finish, I finally had to have my Cat dealer step in and finish the job.

Although a bit reluctant to pick up where others had stopped, the Cat dealer was on the job in a couple of days. Upon inspecting my aftercooler before reassembly, the Cat mechanic discovered that it was defective and had allowed water to enter the engine. Apparently, this was the cause of my problems. How it happened remains a mystery, because the unit had been removed and tested during my 1,000-hour maintenance service, and excessive metal wear had been discovered before then. I gave up communicating with the Cat customer service manager, because he seemed interested only in repeating the official warranty policy.


Despite the frustrations, the final result of my experience was extremely positive. Sawdust’s engine now is essentially a new one, with all major parts having been replaced or inspected. The total cost was $26,000, including the new aftercooler, which cost nearly $3,000.

The engine runs beautifully and even burns a bit less fuel at cruising rpm than before. I’ve been advised by my Cat dealer not to bother with a new oil sample until I have 100 hours or so on the rebuilt engine, but based on how it’s running now, I would not hesitate to run offshore. Sawdust feels like a new boat.

I also learned a lot from this experience. To begin with, I am a believer in oil sampling and analysis. My last report from Blackstone Labs before the rebuild had stated: “These metals show poor wear at the upper end in this Cat, possibly piston scuffing.” This was a warning that turned out to be accurate. Oil sampling may very well have saved me from experiencing a power loss or total failure at an inopportune moment.

Secondly, I’ve decided it’s best to have Cat’s service people work on my engine whenever possible, even if it costs more. While I am sure there are many good independent mechanics, it can be hard to pick the right one. As I found out, the wrong ones can be undependable and accountable to no one. Lastly, if I were buying or building another new boat that had power requirements similar to Sawdust’s, I would take a close look at what other engine manufacturers besides Caterpillar have to offer. And I would make sure their customer service reps give out their telephone numbers.