Cease work and turn off the engine when you see these red flags on an oil analysis report

Updated Mar 20, 2020

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Oil analysis can show you trends in the health of your engines and oil. It can also tip you off to eminent catastrophic failure.

If you catch these problems early enough, you can fix the underlying problem, drain and refill the crankcase with new oil, and monitor the results with further oil analysis, saving thousands of dollars in emergency repairs and possibly prevent a ruined engine.


Severe contamination

“A large amount of coolant – ethylene glycol – in the engine oil would be pretty high on my list,” says Stede Granger, OEM technical service manager for Shell Lubricants. That means a leak somewhere between the parts of the engine containing lube oil and the parts of the engine carrying coolant.

Today’s engines have multiple cooling systems – the main radiator for engine cooling, but also oil coolers and EGR coolers as well. A leak in one of these from a gasket or fitting requires an immediate fix. If not, the slow drip of coolant into the lube oil could contaminate the oil, resulting in overheating, corrosion or damage to the engine.

Most labs check for water, but water by itself is not a guaranteed indicator of coolant leaks, says Granger. “As the engine heats up the water and even ethylene glycol will evaporate. But we sometimes see telltale signs of coolant additives, typically potassium or sodium, depending on the type of coolant they’re using.”

Two to four hundred parts per million of potassium or sodium is the upper limit, says Granger. As for water, anything above 500 ppm is cause for immediate corrective action, he says.


Fuel in the oil

Fuel dilution of lube oil is another big cause for concern and can cause engine damage. It has the same effect as water or coolant dilution except fuel doesn’t burn off as easily. Fuel can get into your lube oil through worn or damaged piston rings, leaky injectors, misfires, bad timing or the emissions system.

“I’ve seen some really high fuel dilution levels, up to 10 percent, in the engine oil, so that would be one to keep an eye on,” says Granger. Fuel dilution can lower your viscosity, reducing high-temperature performance which would mitigate the protective qualities of your lube oil, resulting in accelerated wear on the engine.

Modern engines are getting better. Exhaust blow-by has been reduced, fuel injection is more precisely controlled, and ring packs have been improved. But unlike water, which burns off as the engine heats up, fuel dilution is accumulative. “It’s not as big a problem as it used to be, but it’s still something to look out for,” says Granger.



Not all vandalism shows up as spray paint and smashed glass. Vandals and disgruntled employees have been known to put water, molasses, even DEF fluid in the fuel tank of an idle truck or piece of equipment. And when any foreign substances get into the fuel, they can overwhelm the lube oil’s ability to protect the engine, Granger says.

Oil analysis can detect this contamination, but given the time between oil changes today (as much as 500 hours of engine time), you may not catch it right away. If you’re having engine failures you can’t diagnose, get a quick oil sample and look for any anomalies or spikes in the trend lines. Excessive water or a crazy viscosity number may indicate vandalism, says Granger.



Silicon is another contaminant to keep your eye on. It typically comes from one or two sources. One source is coolant additives. Old-style coolants had silicon in them, but new extended-life formulations do not. Still, says Granger, some people prefer to keep using the silicate formulas.

The other source is a leak in your air filtration system. Silica is present in the dust typically kicked up on jobsites. Today’s air filtration systems do a great job of eliminating this contaminant from your engine’s air stream, Granger says. But a hole in your filter media or a leak in your system can cause a sudden spike in silica levels.

“When I see silica levels above 10 ppm, then it gets a little concerning,” says Granger. “At 400 to 500 ppm, those silica particles could literally be sandblasting the inside of your engine.”


Wrong oil

The current API CK-4 certified lube oils will work in most heavy diesel engines, but there’s a possibility somebody might fill with the wrong product during an oil change. In this case, the oil analysis will show additives like zinc and phosphorus present in amounts clearly not indicative of OEM-recommended engine oil, says David Fields, manager Cummins OilGuard. This may cause a variety of problems, even major engine wear or failure, depending on the fluid used, says Fields.


Skipped oil change

Overly degraded oil caused by excessive duty cycle or going beyond recommended oil drain intervals can lead to high oil oxidation and viscosity, says Fields. This can also happen when somebody skips or forgets a scheduled oil change. Degraded oil can cause lead or copper corrosion in bearings and bushings, which will show up as a spike in the wear metals on the next oil sample. The thickened oil can also harm the lubrication system.


Important but not always critical

In addition to various forms of contamination, you should check  viscosity, total base number/total acid number (TBN/TAN), soot levels  and oxidation. One reading won’t tell you much, but by doing an oil analysis with every oil change, you can see trends in these parameters over time that can help you fine-tune your maintenance program.

A successful oil analysis program requires good practices and recordkeeping and a bit of knowledge about what the results mean. But it’s nothing you can’t learn from a good provider. Choose a lab that will red flag any critical issues and work with you to expand your knowledge of this essential measure of your fleet’s health.