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ETC Extended Oil Change Intervals

DTSC High-Efficiency Oil Filter Study Results

A recent study (Link removed – destination no longer available) provides strong evidence that oil analysis programs, higher quality motor oils, and more efficient filters will protect engines from wear and lead to significant cost savings. Less frequent oil changes will also help to keep fleets on the road and reduces motor oil and labor costs. Oil analysis helps to determine the optimum oil change frequency and can provide early diagnostics for engine wear.

The Study

The two-year study conducted by the State of California examined motor oil longevity in a variety of vehicles, ranging from passenger cars to large diesel engine busses. The 120 vehicles studied accumulated a combined total of nearly 3 million miles. Laboratory analysis of the motor oil tested during use lead to some surprising findings.

  • Finding 1 For any type of vehicle, oil change intervals can be simply and safely extended beyond their current level to the maximum mileage recommended by the vehicle/engine manufacturer.

    A fleet managers’ survey showed an average oil change interval of 4,460 miles for passenger vehicles before the study. This is well below the manufacturers’ recommended 7,500 miles for these vehicles. The oil analysis results showed that oil change intervals can be extended beyond warranty limits to 10,000 miles or more. 

  • Finding 2 Fleet managers can further extend oil change intervals by using higher quality oil and by using oil analysis.

    The study found that higher quality oils can extend the life of engine oil especially those with higher amounts of additives. Routine oil analysis indicates that many current synthetic oils effectively protect engines from wear with oil change intervals at 15,000 miles. 

  • Finding 3 In larger engines, high efficiency oil filters are effective, economical, and will further extend oil change intervals.

    High efficiency oil filters remove small damaging particles, such as dirt and soot which accumulate rapidly in large diesel engine oils. Not only does the motor oil last longer because it is cleaner, engine wear is reduced.


The following chart shows results of three classes of vehicle types studied, and the considerable oil life extension obtained based on oil analysis results.

Type of Vehicle

Original Change Intervals (miles)

Study Proposed Change Intervals










Mileage can be extended furthest in gasoline engines by using higher quality motor oils containing a high total base number (TBN). Using HE filters, oil change mileage can be tripled in Utility trucks. The largest diesel engines can go 50,000 miles or more using high efficiency filters which maintain high TBN.


Oil life extension is economical and has a realistic payback for most vehicle types. Warranty requirements and further information can be found at for most automobile and light duty trucks. Payback periods for fleets using HE filters ranged from 1.3 years to 6.8 years. The payback period was dependent on engine size and change interval extensions achieved. As fleet managers become comfortable with oil change extensions, they typically reduce the number of oil analyses they need to determine if the oil continues to protect the engine. This not only reduces motor oil testing costs, but labor as well. For further details on the study, view the Executive Summary and the Full Report.