Today's diesel engines have longer factory-recommended oil drain intervals than ever before, and now it's more essential for the truck owner to know the condition of his oil and what's happening inside the motor.

Motor oil has a difficult job.

It has to lubricate and cool hot metal and carry contaminants away from those metal parts. It has to do its job in freezing cold, blistering heat and all the temperatures in between.

Fuel or coolants that leak into it can dilute oil and it has to perform in spite of dirty filters that don’t clean it. Even in normal operation, the engine produces soot that thickens the oil and hinders oil circulation.

The interesting thing is that oil itself doesn’t wear out. But it can be damaged through abnormally high temperatures, and its additives degrade as the chemicals absorb contaminants.

Today’s diesel engines have longer factory-recommended oil drain intervals than ever before, and now it’s more essential for the truck owner to know the condition of his oil and what’s happening inside the motor.

That’s where oil analysis comes in. It helps the owner know when it’s time to change the oil and filters. But equally importantly, analysis sometimes says that those components need to be changed more often. Regular oil analysis is an even better safety net than frequent oil changes.

Oil analysis will reveal:

Condition of the Oil

The viscosity of the oil is determined and the level of oxidation is determined. If the analysis is performed in a laboratory setting, the chemical additives are determined, but those chemicals’ lifespan cannot be forecast.

As reported previously, oil can become too thick to flow properly when it becomes saturated with soot or when high temperatures make it oxidize. On the reverse side, oil can thin out if it has been exposed to extreme heat or if there are leaks of raw fuel or coolant into the engine.

Oil thinning can also be caused by bad injectors that fail to atomize the fuel properly or by excessive cold weather idling. Thin oil won’t produce a thick enough oil film on engine parts to protect them from wear.

Oil analysis will show if the viscosity of the oil has changed up or down one viscosity grade, meaning it’s time for to change the fluid. The analysis will even tell you just why the oil has gotten thick or thin.


The presence of foreign matter and chemicals in the oil test sample can reveal a variety of problem areas:

The presence of high levels of combustion by-products such as soot, sulphation and nitration may indicate a number of problems including blow-by, overloaded operations, a too-rich fuel-air mixture and other issues.

Water can come from a faulty crankcase ventilation system, damaged head, block, coolant jacket, oil cooler, heat exchanger, etc.


Particles or traces of a variety of metals such as iron, chromium, copper, aluminum, silver and other metals can determine engine wear and even help to pinpoint the location of that wear.

Additional properties discovered in the oil analysis would include:

Total Base Number (TBN)

Oil’s function is to lubricate, clean, and cool the engine. Additives are added to the oil to enhance those functions. If the oil becomes too acidic, it will corrode the engine.

A total base number measures the amount of active additive left in a sample of oil. Awareness of the TBN is useful for owners who want to extend their oil usage beyond the normal range. The TBN is one of two “neutralization number” tests run on oils.

The TAN (total acid number), which is used for hydraulic oils, is the other. The TBN measures the total basedity of an engine oil; that is, how much base (as in, a base vs. an acid) additive is in the oil to offset the deleterious effects of acids coming into the oil from combustion and other sources.

Oil Analysis for Used Trucks

Oil analysis isn’t just for the owner-operator who wants to keep a close eye on his equipment investment. It can also be a useful tool when evaluating a used truck’s engine.

Warm the engine up, pull the drain plug and watch it drain. Does it flow freely? If not, it’s likely severely sooted up or oxidized.

Then look at the sample and smell it. The experts tell us that the oil will look milky if there is water in it. If it smells like diesel fuel, the engine almost surely has a leaky or malfunctioning injector. If the oil is pink or green, it probably has a coolant leak. Get the oil sample to a testing facility.

That one-time sample may not reveal trends within the engine such as accelerated wear due to poor maintenance or other causes, but it will give you a starting point in determining the engine’s health.

A Speedy Oil Analysis Solution

In a survey of expediting owner-operators, it was discovered that a number of them have become regular customers of the Indiana-based Speedco oil and lubrication outlets. In addition to using Speedco’s regular oil change services, the owners are also using the company’s oil analysis service as well. Figures from the company show some 20 percent of Speedco customers elect to have the oil analysis performed.

Jim Hutchek is with the Marketing Department of On-Site Analysis, the firm that provides the oil analysis and testing equipment to Speedco. He compares the oil analysis process to going to a doctor and getting a blood test.

He states, “Speedco is able to perform the same level of tests that were previously only found in an oil testing laboratory, the difference being that the oil test results are immediate and on site. It’s all about identifying small issues before they become big problems.”

Pat Smythia is the owner of Freedom Express, a fifteen truck fleet leased to several expedited carriers. She says, “Because of the convenience of their locations, our drivers usually use Speedco for the oil changes. I feel that the oil analysis service tells us if we’re doing things right and it helps give me control over the fleet’s maintenance.”

She adds, “We often use it once or twice a year for the older trucks in the fleet, particularly when they get close to the end of their warranty.”