Oil Drain Intervals

How to maintain engine performance and maximize useful service life through optimizing oil drain intervals.

Many engine manufactures now have varied drain intervals that are dependent upon the severity or level of vehicle service, weight of load being hauled, fuel economy, idle time, service environment, etc. By way of example, Arcy of Shell cites a Cummins ISX diesel engine used in on-highway service. The recommended oil change is 15,000 miles for severe duty, 25,000 miles for normal duty and 35,000 miles for light duty.

The conditions of severe service promote higher fuel consumption which leads to increased engine oil contaminants, oxidation and acidic compounds, notes Betner of Citgo, all of which accelerate the deterioration of the oil and potential loss of engine protection.

While accurately determining a vehicle’s service level is important to help maximize engine life, as well as the optimum drain interval for the engine oil,” Chevron’s McGeehan says “the overriding factor may be maintenance practice.”

“Often an equipment owner will ask how far I can go on your oil,” observes Citgo’s Betner. “This is like asking a doctor how you will do in a marathon race. An irresponsible doctor would tell you something like this: ‘Well, you appear to look great, so I believe you will do just fine.’ The same is true of any engine oil manufacturer attempting to make an engine oil change interval claim without knowing the critical operational facts.”

When selecting an engine oil, each of the oil manufacturer representatives emphasizes choosing premium engine oils. These oils have been formulated with the most technologically advanced additives and premium base oils to provide the maximum protection required to combat oxidation, shear, wear, soot, corrosion, etc., that breakdown an engine oil over time and cause it to become less effective.

To optimize engine oil change intervals, in addition to factoring in operating conditions, Betner of Citgo advises working closely with engine, engine oil and oil analysis providers. “Equipment owners have large capital investments in equipment and the cost of engine oil is only 2 cents of every operating cost dollar,” he says. “It does not make sense to think that the equipment owner is saving money by trying to get by with cheaper performance levels of engine oil.”


The use of synthetic engine oils has been growing because of the advantages they provide over conventional (mineral) engine oils. Synthetic oils are formulated using a percentage of Group III and/or Group IV base oils, while conventional oils are formulated using Group 1 and/or Group II/II+ base oils, explains Chevron’s McGeehan. (Base oils are categorized by their properties.) Synthetic oils are generally more stable at both low and high temperatures and have better oxidation resistance, but are significantly more expensive than mineral oils.

Synthetic blend SAE 10W-30 or 10W-40 diesel-engine oil may offer extended-drain capability, enhanced engine cleanliness and excellent wear protection in the hottest summer heat and the coldest winter freeze, Shell’s Arcy says. “This is possible through a combination of additives and synthetic-blend base oil. Synthetic blend oil provides protection in critical areas by helping to control acid, deposits and wear. It also helps protect against acids which are formed as fuel burns. Wear control also contributes to engine life by keeping metal surfaces apart.”

Synthetic blends are often offered in lower-viscosity grades such as SAE 10W-30 or 10W-40, compared to conventional SAE 15W-40 oil, so it will thicken less at colder temperatures, notes Arcy. “Quick oil flow in the engine at startup is particularly important in cold-climate conditions. A synthetic blend SAE 10W-40 or 10W-30 flows better than conventional SAE 15W-40 diesel-engine oil in a cold engine.”

Synthetic blend engine oil also maintains its viscosity under high temperatures, he says, allowing it to provide strong protection under hot operating conditions. “Increased fuel efficiency is possible with synthetic blend SAE 10W-30 engine oil when compared to conventional SAE 15W-40 engine oil because it can increase flow capability, thereby reducing the energy used to pump the oil through the engine.”


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