Tech Tip: What is Acceptable Oil Consumption in Diesel Engines? – UnderhoodService

Tech Tip: What is Acceptable Oil Consumption in Diesel Engines?

There's no simple answer to that question. Many factors can contribute to oil consumption, and correctly diagnosing if there is a problem and what's causing it can save you a lot of money and down time. All engines will consume some amount of oil, and as an engine ages and wears we generally accept increases in consumption, but in low mileage or low hour engines oil consumption can be frustrating.

What is Acceptable Oil Consumption in Diesel Engines?

There’s no simple answer to that question. Many factors can contribute to oil consumption, and correctly diagnosing if there is a problem and what’s causing it can save you a lot of money and down time.

All engines will consume some amount of oil, and as an engine ages and wears we generally accept increases in consumption, but in low mileage or low hour engines oil consumption can be frustrating. Letting an engine with truly high oil consumption go unchecked can result in shortened engine life and/or engine failures.  

External oil leaks are the easiest to identify and shouldn’t be underrated. A few small external leaks can add up to a considerable amount of oil over time, and obviously these can lead to safety concerns.

Internal oil leaks that allow oil into the combustion chamber from rings not seating due to improper break-in procedures, incorrectly installed rings, leaking turbo seals, worn valve train components, etc…are harder to identify and more expensive to repair. It’s not always major problems, something as simple as: a failing air compressor, wrong type/weight of oil, or over filling the crank case can cause oil consumption.

Before an engine would be disassembled a study should be done to track the actual amount of oil usage and determine if the engine truly is consuming questionably high amounts of oil.

There are different methods to calculate excessive oil consumption. Some deal with calculations involving load factors and BSCO (brake specific oil consumption) and grams per brake horsepower hour (g/bkW-h) or pounds per brake horsepower hour (lb/bhp-h). Combining the O.E. information, we’ve found the simplest guideline we’ve developed is shown in the chart below. The chart (see illustration above) compares the engines fuel usage in comparison to its oil consumption. Oil usages should be recorded over at least two consecutive regular service oil change periods to determine a reliable base line.  
 
There are conditions and circumstances where engines falling in this questionable range could still be within acceptable limits.

Obviously operating conditions can play major roles and consideration must be given to things such as:  
• Load factors;
• Oil density and additives;
• Operating practices;
• Operating temperatures;
• Maintenance programs and practices; and
• Equipments applications.  
 
Taking the time to investigate and understand the problem can save you time and money. In some applications and environments the demands placed on the engine can contribute to the additional oil consumption and additional “repairs” to the engine may not produce improvements.  

The guidelines above are to be used as a reference. Refer to the latest O.E. manufacturer’s bulletins and publications for more information.  

Tech Tip courtesy of IPD, www.ipdparts.com.

You May Also Like

Diagnosing Intercooler Boost Trouble Code P0299

The criteria for setting the code is very basic.

A code P0299 for lower- than-normal boost can be one of the most challenging DTCs to resolve. You might think it is a code for a leak, but it could be more than a leak. The criteria for setting the code is very basic. The engine management system is looking at the desired boost pressure and the actual boost pressure, if the actual and desired do not match for the conditions. 

Honda Electronic Throttle Body Service Tips

Using care and following OEM procedures will help you to avoid unnecessary parts replacement and comebacks.

Why Alternators Are Subject To Ripple Voltage

The alternator produces an AC current that must be converted into DC current by way of a rectifier.

Belts and Pulley Alignment

A misalignment of the plane of the belt can occur when a pulley is not parallel to the other pulleys on the belt drive system.

Diagnosing Misfires

What if there are no codes and a misfire is intermittent? This is where it gets complicated.

Other Posts

Lifter Deactivation

The area of contact between the lifters and cam lobes is the highest loaded surface inside an engine.

Alternator Testing For No Charge Conditions

Many alternator problems turn out to be nothing more than a bad connection at the alternator or a bad wiring harness.

Understanding Coolants

All-season coolant used inorganic acid technology and worked great for almost 30 years.

Ignition System Do’s and Don’ts

Why do ignition systems give technicians problems when diagnosing ignition-related misfires? The answer is that some technicians use tests that might give inconclusive results or do damage to the coil or drivers inside a module.