Maximizing ERV Motor Oil Drain Intervals Using Fluid Analysis

By Christian P. Koop

The physical task of changing motor/engine oil has remained basically unchanged for more than a century. However, the oil, or lifeblood of your engine as I and others like to refer to it, sure has changed. Failure to change this modern marvel of petroleum and chemicals at the appropriate time will still render the same results today as it did more than a century ago. It will shorten the useful life of your engine, and if the wear and damage caused by failing to change the oil at the proper intervals requires the engine to be overhauled or replaced, it will be one of the most costly one-time expenditures to hit your maintenance budget.

With today’s tight budgets, we need to ensure we change oil at the optimal time. Changing it too frequently, in the long run, can cost your operation significantly-both in wasted labor hours and in money spent needlessly on oil and filters. The key is to find the right time to change it. Think of it as the proverbial sweet spot. The best way to do this is by using fluid analysis. Given the complexities of today’s engines, whether your fleet is large or small, analyzing your fleet’s motor oil is the best practice-not only in finding that sweet spot but also in alerting you to prevent catastrophic engine damage in many cases.

In this article, I will talk briefly about the history of motor oil, some of the main additives in motor oil, what they do, and how some of the information fluid analysis reports will help to proactively protect and prolong the life of your emergency response vehicle’s (ERV) most vital component-the engine-whether it is gasoline- or diesel-powered.

Motor Oil

Everyone knows that motor oil’s main job is to lubricate moving parts. But, don’t forget it also helps to cool, improve sealing, and clean the engine. Oil essentially has a long molecule, and we change it because it gets sheared (loses viscosity), dirty, thicker, and contaminated and its additive packages get used up. The chemical makeup and the improvements of motor oil have changed dramatically over the years.

Many years ago, motor oil was completely derived from crude oil. The problem was that during the combustion process and the normal use of those early engines, oil broke down quickly, viscosity decreased, sludge and varnish formed, and acids were created that attacked vital engine parts. One of the most important requirements discovered in the early years of the automobile for motor oil was the need for proper viscosity. The oil had to have the correct thickness or viscosity (measured by resistance to flow) to ensure metal parts, such as engine bearings, would not come in contact and cause damage.

The Society of American Engineers (SAE) was formed in 1905 and developed standards for motor oil viscosity ratings. The SAE, as most are aware and familiar with, continues to provide these standards. In 1919, the American Petroleum Institute (API) was established to set the minimum performance standards for motor oil that continue to evolve today. It currently licenses and certifies motor oil and appears on oil containers as a “starburst pattern” and the “service donut” symbol.

In the early 1930s, oil additives started to appear that greatly improve the performance of oil and eventually add more protection and prolong engine life. Some of these additives follow:

  • Typically detergents are made from magnesium sulfonate and are used to clean and prevent sludge from forming.
  • Corrosion inhibitors slow down the oxidation of metal inside the engine.
  • Amines and phenals are antioxidants that retard the degradation of the base oil caused by oxidation.
  • Metal deactivators are used to form a film on the metal parts to stop the metal from oxidizing the oil.
  • Viscosity modifiers help to maintain oil at the correct viscosity at higher engine temperatures.
  • Pour-point depressants are used to help the oil flow at very low temperatures and are used to formulate multigrade oils in combination with viscosity modifiers.
  • Molybdenum disulfide is used as a friction modifier to reduce friction and improve fuel economy.
  • Zinc dithiophosphates or zinc dialkyldithiophosphates are used as antiwear additives that form a film around metal parts to keep the two in separation, thus reducing wear. The phosphates in these additives are a double-edged sword because they can poison the catalytic converter and reduce its life.
  • Contaminants are suspended in oil by using dispersants.
  • Antifoam additives reduce or inhibit air bubbles from forming, which can lead to loss of lubrication and other issues created by aeration of motor oil.
  • Silicones are used to prevent atomization of the oil.

These additives and various others are used by the oil manufacturers to produce motor oil from petroleum base stock that meets the latest standards required by the many different engine manufacturers and the hundreds of different engines that are produced worldwide today. Without these additives, oil would not be able to protect the modern engine, nor would we see over-the-road truck engines that are capable of going more than 1.5 million miles before the first overhaul.

Multigrade Oils

The advent of multigrade/viscosity oils has allowed engines to start in very cold climates and is also partially responsible for improvements in fuel mileage. They are specifically formulated for many applications including gasoline and diesel engines.

Synthetic oil was developed by the Germans during World War II so engines could start in extremely cold conditions because petroleum-based oil would freeze or become so thick engines could not turn over. There are many types of synthetic motor oil on the market today, from synthetic blended with petroleum base to fully synthetic. Some automobile manufacturers are requiring synthetic oil in their engines because it reduces friction, lasts longer, and improves fuel economy. Some fleets exclusively use synthetic oil and some do not. If you don’t use it and are contemplating its use, the best way to test it in your fleet is by using fluid analysis while comparing it to sister trucks using conventional oil.

Today some manufacturers are requiring multiviscosity grade oils as low as 0W-20. The latest standards for gasoline engines are currently SN, and for diesel it is CJ-4, which became effective in 2006. There are also other agencies that provide standards such as the International Lubrication and Standards Committee (ISLAC), the equivalent for this agency in Europe is the European Automobile Manufacturers Association (ACEA). ACEA came up with a new standard for model year 2011. To add to the confusion, General Motors no longer supports ISLAC and has come up with a new engine worldwide oil specification of its own named dexos 1, which the company recommends for all its 2011 model engines.

Fluid Analysis

Let’s take a look at what a fluid analysis laboratory will generally test if you are looking to safely extend the drain interval. The basic analysis should include all wear metals, contaminant metals, and metals used for the additives in the oil. Along with these basic tests, fuel dilution (how much fuel is in the oil) and soot levels in the oil, which are both measured as percentages, are very important. If fuel dilution is not detected in time, it can lead to low oil pressure and eventual catastrophic failure. I have personally seen a case where the fuel dilution had raised the oil level so high in the crankcase it blew out the dipstick, and engine oil sprayed out of the dipstick tube onto the hot turbocharger, where it ignited and caused a fire.

There is even one diesel engine manufacturer that fires the injectors on the exhaust stroke to provide the fuel dosage needed for the diesel particulate filter (DPF) to perform the regeneration cycle. This design will inherently have a higher percentage of fuel dilution over those engines that inject diesel directly into the DPF with a dedicated injector. And with this design, it becomes even more critical to know the percentage of fuel dilution. The oil’s viscosity is tested at 100°C under the ASTM D-445 testing standard. Nitration and oxidation are both similar as they are a direct result of components in the oil being exposed to nitrogen oxide and oxygen during the combustion process. Both may lead to increased viscosity, acid formation, varnish, sludge, increased sediment, and other contaminants that will affect the life of the oil and the engine.

Total base number (TBN) and total acid number (TAN) are also very important in determining when the motor oil should be drained. Don’t be intimidated by all the preceding chemical and technical information, as lab reports will help you interpret the information and will let you know if the oil is still good for continued use. A word to the wise: If you are analyzing your oil or are thinking about doing it, make sure the lab is accredited under ISO 17025.

Oil Change Intervals

Today the improvements in motor oil coupled with better metallurgy and tighter tolerances in the machining process, low tension piston ring packs, along with larger capacity oil pans have increased the oil drain intervals considerably. This is particularly true for over-the-road trucks. However, if your ERV is mainly used in inner city severe stop-and-go traffic, your oil change intervals may need to be adjusted.

Following the manufacturers’ recommended oil drain intervals is important; however, you need to understand that they are guidelines. The type of service, climate, and duty cycle your ERVs operate in need to be taken into account. Knowing the right time to drain the oil, whether you are using engine hours, mileage, a combination of the two, or even basing it on fuel consumption, will save you dollars and extend your engine’s useful life to its maximum potential.

Factors that affect why and when you should change your oil include how many times the engine starts cold, the ambient temperature, how well the crankcase is being scavenged via the positive crankcase ventilation (PCV) system (in the case of a gasoline engine), and the mechanical condition of the fuel injection system and how precisely it is working. Last, the distance traveled in miles or hours of operation also falls into the equation and needs to be monitored.

Obtaining Samples

The oil sample should not be taken from oil that is drained from the bottom of the engine oil pan. We take our samples from a brass shutoff valve installed in an engine oil galley plug with the engine running and at operating temperature. The labs generally provide the sample bottles, which in our case includes postage. We normally take samples when the vehicle is scheduled for service and send them to the lab through the United States Postal Service.

The labs provide both a hard copy of the report, which is mailed to the customer, and an electronic version sent via e-mail. If the oil is still good for continued use, it will be noted. If the labs find a critical condition during testing, such as excessive fuel dilution or high levels of silica (dirt/sand), they will notify the customer immediately. If you need help interpreting the data on the report, the labs’ technicians or representatives can help in this area.

If you are not analyzing your oil, I recommend some random testing to evaluate your fleet to see if you can extend the drain interval. Keep in mind that maintaining proper viscosity is still one of the most important factors for motor oil, and the best way to keep tabs on it and safely extend your drain intervals is by using a laboratory to analyze your motor oil.

CHRISTIAN P. KOOP is the fleet manager for the Miami-Dade (FL) Fire Department. He has been involved in the repair and maintenance of autos, heavy equipment, and emergency response vehicles for the past 35 years. He has an associate degree from Central Texas College and a bachelor’s degree in public administration from Barry University and has taken course work in basic and digital electronics. He is an ASE-certified master auto/heavy truck technician and master EVT apparatus and ambulance technician. He is a member of the board of directors of EVTCC and FAEVT and a technical committee member for NFPA 1071, Standard for Emergency Vehicle Technician Professional Qualifications.

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