Excessive Oil Consumption Explained 

Is your diesel engine consuming oil at a higher rate than normal? This could be due to normal engine wear, but it also might indicate an issue. Read on to find out more about what could be happening in your diesel engine!

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What is Excessive Oil Consumption?

Excess oil consumption is any oil consumption above an acceptable range during normal operating conditions. Each engine will have a natural and acceptable amount of oil consumption, which you do not need to worry about. Any consumption above these given levels is excess consumption and should be addressed. Below are some common reasons why diesel engines will consume oil.

Why an Engine Will Consume Oil | Highway & Heavy Parts

Factors that Affect Normal Oil Consumption

There are several reasons that an engine will consume oil that are normal, and do not signal that something is wrong.


Engine Age

The amount of oil an engine consumes will naturally change with the life of the engine. At the beginning of an engine's life, it will have a break-in period in which it will consume a higher level of oil. To help quicken this period, refer to our blog on the engine break-in process.

After an engine is fully broken in, it will consume less oil. The consumption will stay at that rate for a while. Once the engine begins to come to the end of its life cycle, the rate of oil consumption tends to rise again.


Increased Demand

An increase in the demand placed on an engine will also increase the oil consumption. Things such as heavy loads and extreme conditions will increase the demand on an engine. An example of an extreme condition is operating in mountainous terrain. The harder an engine has to work, the more oil it will consume.


Oil Viscosity

The viscosity of the oil you use in your engine will also affect how much oil your engine naturally consumes. Lighter viscosity oils will be consumed in slightly higher amounts. For example, if you change from a 15W-40 to a 10W-30, your oil consumption will increase.


Oil Change Intervals

Changing your oil in the proper intervals will also help with oil consumption. The further you extend past your recommended oil change interval, the higher the rate of oil consumption. If you have recently rebuilt your engine, be sure to alter the oil change intervals for the first few changes. For more details on that, see our oil change intervals after diesel engine break-in blog.


Reasons for Excessive Oil Consumption

If the engine is being run under normal conditions, excess oil consumption is generally a mechanical problem. Before you can begin troubleshooting, you must first determine in what way the oil is being consumed. Oil consumption can happen from either leaking or burning.


Leaking Oil

In most instances of oil consumption, it turns out to be a leak issue. Usually the valve cover gasket of one of the main seals is the source of the leak, but it can also pretty commonly be from the oil pan gasket.


Burning Oil 

In fewer instances of oil consumption, it can be an issue of the engine burning the oil. The engine will burn oil if the oil gets up into and past the piston ring and ring belt areas. While these areas are clean, there will be fewer carbon deposits and less oil will be consumed. When these areas get dirty and covered with carbon, the rings cannot move freely and the oil will get past the rings, where it will get burnt away.

The quality of the oil you use in your engine can help keep it from burning. Higher quality oil will help keep the piston ring and ring belt areas clean, and decrease the chances of your engine burning oil.


Reasons for Burning Oil

Listed below are some of the more common reasons that your engine oil could burn away.

Dirty Oil 

Dirty oil is a very preventable cause of oil consumption. If the oil is not changed at proper intervals, or proper care is not taken of the oil filter, the oil will accumulate debris that causes the oil passages in the piston rings and pistons to clog. This will increase both oil consumption and wear on engine parts. Dirty oil will wear on bearings, cylinders, pistons, and piston rings. The more these parts are worn, the more oil will be wasted in turn.

Too Much Oil in the Crankcase 

Oil can be burned when there is too much oil in the crankcase. If there is so much extra oil that the lower ends of the connecting rods touch the oil in a pressure lubricated engine, or the dippers go too deep into the oil in a splash lubricated engine, excessive quantities of oil can be thrown onto the cylinder walls and work their way up to the combustion chamber. When checking your oil level, be sure to insert the dipstick so that it comes to a seat on its shoulders, guaranteeing an accurate reading. Too much oil can be added due to an inaccurate low reading.

High Engine Vacuum 

Engine vacuum has increased in newer engines as engine RPM, valve overlap, and compression habits have increased. While older engines would draw maybe twenty inches of vacuum on deceleration, some newer models can draw as much as twenty-five inches. This increase in vacuum has called for the development of an oil ring to seal both the top and bottom sides of the ring grooves and eliminate oil from passing around the rear and sides under high vacuum or deceleration. This vacuum could be the main cause of smoking and oil consumption, so it is important to use a side sealing piston ring when the application requires it.

Worn Timing Gears 

Timing is incredibly important in the function of engines. When motions are not perfectly harmonized between the valves and pistons, a vacuum can be created that draws large quantities of oil into the combustion chamber, causing very high consumption. One cause that can lead to the timing being off between valves and pistons is worn timing gears, which throw off the valve and crankshaft timing and create a large amount of backlash.

Too Little End Clearance of Piston Rings

Piston rings need a sufficient amount of end clearance to account for heat expansion, and this must be accounted for when fitting new rings. The rings are exposed to the direct heat of the burning gases in the combustion chamber, and so heat more rapidly and operate at a higher temperature than the cylinder itself. The cylinder walls are cooled by the water in the water jacket, which helps keep them at that lower temperature. Due to the difference is temperature, the rings expand much more than the cylinder, and the end clearance (the gap between the two ends of a ring) is what accounts for this expansion. If the rings do not get this clearance, their ends will butt up against one another while the engine is operating. This contact will cause scuffing and scoring of the rings and the cylinders, which in turn causes oil consumption.

If this situation occurs for continued operation, and especially under a heavy load, the scoring will be even more severe. The ends of the piston rings can be forced inward, toward the piston, creating an open space between the rings and the cylinder wall. Oil and hot gases come throughout this gap to burn oil at a high rate.

It's important to note that too much piston ring end clearance will also result in oil consumption, as that can leave a gap between the rings through which oil and gases can pass.

Worn or Broken Piston Rings 

When piston rings are broken or worn enough that proper tension and clearances are not maintained, they can allow oil and hot gases to pass by them. The oil will be drawn into the combustion chamber during the intake stroke of the engine, and the hot gases can be drawn underneath the piston during the power stroke. Either of these will result in oil burning and carbon being deposited on the cylinders, pistons, and rings.

Broken rings will do even more damage than that stated above. The jagged ends of where the rings are broken can cut into the piston grooves, which can potentially cause land breakage. Land breakage, in turn, will completely destroy the piston assembly. Often, piston rings break because they were not replaced during an overhaul. It is always a good idea to replace your piston rings when taking apart the cylinder. In fact, any rebuild kit you buy from HHP will include piston ring sets. Our smallest level of rebuild kit is even named a re-ring kit because of how important it is to replace the rings, even if you reuse the pistons.

Piston Rings Stuck in Grooves 

Have you noticed yet the importance of piston rings? If not, we've got another one for you. Piston rings that get stuck in the pistons grooves can't do a whole lot to manage the oil in the cylinder. Here are some things to keep in mind that will prevent the rings from getting stuck in the grooves:

  • Install the rings so that they have enough side clearance to remain free while the engine is operating at normal temperatures.
  • When assembling the piston assembly and cylinder, take every precaution possible to keep the parts clean. Even a few tiny dirt particles can cause the rings to stick.
  • Use a good grade of oil. As tempting as it is, don't cheap out. Better grades of oil lessen the possibility of carbon or varnish.
  • Again, be sure to get oil changes at the proper time and take proper care of the oil filter. We cannot stress enough how important oil changes are.
  • Try to avoid overheating the engine. This is great advice for many reasons, but it also applies here.


Oil Pressure Too High 

When the oil pressure is too high, the engine can flood with an abnormally large amount of oil. This excess oil can get thrown into the cylinders, where it will be burnt away. Sometimes high oil pressure can be caused by an incorrect oil pressure setting or a faulty relief valve.

Lugging Engine

Lugging an engine is running it at a low RPM where more power and torque is needed. Forcing the engine to work harder than necessary causes stress loading on the piston and will increase oil consumption.

Restricted Air Intake

Any kind of restriction on air intake will create a vacuum that will draw oil into the combustion chamber. Whether the restriction is due to carbon deposits blocking air passageways, as mentioned above, or a heavily plugged air filter, the same kind of vacuum is created.


Consequences of Low Oil Levels 

If you are low on oil, the engine puts extra stress on the oil that you have left. Any additives in the oil are going to be consumed at a faster rate if the engine is run with low oil, which reduces the life of the oil you do have.

If your oil level is low because the oil is burning, it may cause additional problems to these. If your engine is burning oil, carbon deposits can form on the valves and in the combustion chamber. If oil makes its way into the combustion chamber, it can cause deposits on the top of the pistons. The carbon deposits in these locations will lessen the airflow into the cylinder, which results in power loss and overall poor engine performance.


Need help finding parts to fix your excessive oil consumption? Give our ASE Certified Techs a call at 844-304-7688. Or, you can request a quote online.


Originally Posted August 30, 2017 ; Edited November 6, 2020