Oil Sample Analysis

Oil is the lifeblood of your engine, and like a blood test for the skipper, an oil analysis can identify potential problems before they become major ones.

Story And Photos By Alison Mazon

Photo of boat engine oil

A lot goes on inside your engine. Pistons race up and down, valves snap open and closed, gears spin — and everything's working at breakneck speed to produce the power you need to propel your boat. Because all of this happens deep in the hidden bowels of your engine, you may never know if a problem is developing until one day it just quits. Having your engine or transmission oil professionally analyzed can tell you what's really going on inside and alert you to potentially serious problems.

How It Works

An oil sample analysis (OSA) evaluates the levels and types of metals and the presence of such contaminants as abrasives, soot, water, fuel, and engine coolant in the oil of gas and diesel engines. A lab report will flag any suspected anomalies, state possible causes, and offer some plain-English recommendations. Typical conditions that can be found by analysis include abnormal wear of metals, fuel dilution, dirt or water contamination, coolant contamination, and incorrect lubricant. Discovering any out-of-range condition early can prevent expensive repairs later on. For instance, fuel dilution will accelerate cylinder and bearing wear. High levels of solids will cause wear on bearings, pistons, cylinders, and the valve train. Excessive soot in a diesel engine can be caused by dirty injectors, weak ignition, low compression, or restricted intake or exhaust, among other things. Simply servicing a dirty injector can save an engine rebuild if caught in time.

Most OSAs will include the following:

  • Spectral Exam: A spectrometer is used to find the quantity of various metals and additives in the sample — useful for finding excessive wear in bearings, pistons, rings, cylinders, valve train, and gears. It also determines the composition of any oil additives.
  • Viscosity Test: The thickness of the oil at a specific temperature is tested — useful for finding fuel dilution, the breakdown of viscosity enhancers, or other contamination.
  • Flash Point: Tests the temperature at which vapor from the oil ignites — contamination can cause a specific grade oil to flash higher or lower than the design flash point.
  • Insolubles Test: Insolubles are typically abrasive solids — high readings are usually byproducts of incomplete combustion.

OSA is more useful as a tool to monitor a specific engine and/or transmission over time rather than as a one-time evaluation. Small changes, which may not look significant in a single analysis, will stand out if there are prior samples on record. For example, a higher lead or tin level than in past reports, while still within normal ranges, could alert you to accelerated plain bearing wear. That's not to say that OSA on a one-time basis isn't useful. A single sample (often performed in the course of a pre-purchase survey) will indicate a serious condition that deserves further investigation. However, a one-time analysis has to be carefully reviewed and interpreted prior to waving a red flag. The machinery total hours, type of machinery and use, type of oil and hours on the oil, knowledge of average baselines common to a particular unit—such context is important. This is where you may need the services of a knowledgeable marine-engine technician or surveyor; she can review the report in light of all known information, and then make recommendations.

I've found that many brokers dislike one-time samples because of questions that can arise due to lack of experience and the lack of a detailed service history typical of many vessels. The less knowledge there is about the sample taken, the broader the interpretation of the results must be. I recommend OSAs every year, more often for high-usage engines or for those that have red flags from previous analysis.

How To Take A Sample

I mentioned earlier that a "carefully taken" sample is useful; you wouldn't want your doctor to use contaminated equipment to draw your blood. The same is true for oil sampling. There are some very simple but important steps to ensure the sample taken represents the average fluid in the engine or gear. Sampling mistakes include: getting oil out of a drain pan after the oil is drained, pulling an oil gallery plug and drawing a quantity of oil while the engine is running, sticking a suction probe to the bottom of the oil pan, reusing suction tubing or sample containers, or contamination of the vacuum pump. These can all skew a sample, not only making it worthless but possibly sending you on an expensive trail trying to fix a problem that may not exist.

Most heavy-equipment manufacturers sell suction pumps and oil-sample kits that are convenient and inexpensive. For most marine engines and marine gears, a simple vacuum pump, semi-rigid disposable plastic tubing, and a plastic bottle that can be screwed into the vacuum pump are all you need. The pump is a one-time purchase and can be reused many times. The OSA kits contain a collection bottle with cap, a label to be completed by the person taking the sample, a length of plastic tubing, and a mailer of some type to mail the sample to the lab. The cost for an OSA kit at my local Caterpillar dealer is about $17, which includes processing the sample and sending me the analysis of the results. That's a bargain by any measure.

Photo of oil sample toolsTaking an oil sample is easy with the right tools, and they can be used again and again.

Note: If the fluids have been changed very recently, an OSA isn't likely to be particularly useful except to see if there is something catastrophic happening. Fifty hours in service is generally a suitable time of operation to obtain meaningful results.

Follow these steps to draw a representative oil sample:

1. Run the machinery to warm up the fluid and suspend the particulates.

2. Cut a length of tubing that allows you to extend the tube into the engine or gear and with enough length to allow you to get in a comfortable position to operate the pump.

3. Insert the tubing into the top of the pump so it extends through the pump approximately 1 to 2 inches. Tighten the knurled top so the pump O-ring grips the tubing tightly, ensuring a good seal.

4. Take the cap off the sample bottle, place the cap in a clean location, and screw the sample bottle to the pump.

5. Pull the dipstick, and lay it alongside the suction end of the tubing. Mark off this length on the tubing with a marker or tape so you will know when the end of the tube is far enough into the unit to reach the oil but not too far where it could reach the contaminants that may have accumulated at the bottom. Touching the bottom would likely contaminate the sample, resulting in false readings.

6. You may need to straighten the tubing by applying a reverse bend several times until the portion being inserted is reasonably straight.

7. Carefully insert the plastic suction tube into the dipstick tube just to the mark you made on the tube, and operate the pump. You may have to reinsert the tube a few times in the event it curves and doesn't enter the lubricant, or you may have to insert it a little further than your mark. Just don't go too far.

8. Pump the prescribed amount into the bottle (about two ounces in most cases) but do NOT fill to the top as that would contaminate the pump. Always keep the pump level.

9. When nearly to the correct level, pull the tubing up until it is clear of the sump oil and draws only air. This will clear the tubing of most oil.

10. Cut the tubing off several inches above the pump.

11. Unscrew the bottle, and replace the cap securely.

12. Loosen the pump's knurled top, and push the remaining short section of tubing through the top of the pump and out of the bottom. This will keep oil from contaminating the pump.

13. Clean the pump of any residue. Do not use solvents, as solvent residue could skew future samples.

14. Fill out the label as completely as possible with all requested information. Incomplete or inaccurate information will result in less accurate analysis.

15. Place the bottle with label in the provided container, and drop in the mail, or return it to the equipment dealer where you purchased it.

What you get back is a report that highlights suspected abnormalities, with possible causes and actions for you to take (see a sample report).

Congratulations! You are on the way to establishing a meaningful service record for your equipment. Having a log of OSAs over a period of time can be an excellent sales tool when selling a vessel. It shows the true condition of the machinery, and it demonstrates that the vessel has been well maintained by a conscientious owner. 

Alison Mazon is a SAMS Accredited Marine Surveyor, ASE Master Technician, and former boat repairer from Portland, Oregon.

— Published: April 2015

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