What Causes High Oil Consumption in a Diesel Engine?

If you're suffering from high oil consumption in your diesel engine, meaning your engine is consuming more than the acceptable range of oil during normal operating conditions, then you are in the right place. High oil consumption could affect your engine's longevity, so it's important to identify the cause of your high oil consumption. Let's take a look at six common high engine oil consumption causes so you can resolve the problem quickly. 

Excessive bearing clearance in the turbocharger

During normal driving operation, the bearings in the turbocharger are subjected to high loads. If the turbocharger bearings show signs of wear, the impeller seals will no longer provide a perfect seal because of the increased bearing clearance. Engine oil is then sucked in and burnt in the combustion chamber and the air/fuel mixture.

The oil return line on the turbocharger is blocked

If the oil return line from the turbocharger to the cylinder block becomes too hot, the oil will coke in the line. Coking of the return line prevents the unpressurized return of the oil to the sump. The resulting high oil pressure causes oil to escape at the impeller bearings on the turbocharger. The oil enters the intake tract and is then sucked into the combustion chamber and burnt together with the air/fuel mixture.

Worn injection pumps

The lubrication of the moving parts of an in-line injection pump is usually performed via the engine's oil circuit. Leakages due to worn parts will lead to the fuel and the engine oil mixing. During the fuel injection process, this mixture of oil and diesel fuel is then injected into the combustion chamber and burnt. 

Abnormal combustion and fuel flooding

In the event of faulty combustion due to the combustion chamber being flooded with fuel, unburned fuel remains in the combustion chamber. Any deposits of unburned fuel on the cylinder walls result in mixed friction. The consequences of this are high and rapid wear of pistons, piston rings and cylinder running services, and high oil consumption. 

Valve stem seals and valve guides are worn

If the clearance between the valve and the valve guide is too great, or the valve stem seal has been damaged during the installation, increased oil quantities will escape at this point. Oil in the intake tract is burnt, oil in the exhaust tract is emitted directly. 

If you're suffering from high oil consumption in your diesel engine, meaning your engine is consuming more than the acceptable range of oil during normal operating conditions, then you are in the right place. High oil consumption could affect your engine's longevity, so it's important to identify the cause of your high oil consumption. Let's take a look at six common high engine oil consumption causes so you can resolve the problem quickly.  

Incorrect piston protrusion 

If the piston protrusion is not with the tolerance range specified by the engine manufacturer, the piston may strike the cylinder head. The crankshaft drive is subjected to a large increase as a result. This can cause damage to the crankshaft, pistons and connecting rod bearings or create combustion faults due to incorrectly injected fuel quantities. 

Every engine manufacturer has a range or limit values for the oil consumption of each of their engines. You can usually find this information in workshop manuals or by contacting the OEM directly.

If you can't access this information from the original manufacturer, then you can use this guideline:

Trucks

The usual engine oil consumption ranges from 0.25% - 0.5% in proportion to the actual fuel consumption for trucks. For example, a truck consumes about 40 litres of fuel per 100km, roughly equalling around 400 litres of fuel for 1000 km. 0.25% of 400 litres of fuel is equivalent to an oil consumption of 1 litre. 0.5% of 400 litres of fuel is equivalent to an oil consumption of 2 litres.

Cars

Smaller passenger cars usually consume oil around 0.1% - 0.5% of the fuel consumption. Usually, a passenger car will consume around 8 litres of fuel per 100 km, roughly equating to 80 litres of fuel per 1000 km. 0.1% of 80 litres of fuel is equivalent to an oil consumption of 0.08 litres. 0.5% of 80 litres of fuel is equivalent to an oil consumption of 0.4 litres.

If your oil consumption is excessive, you will not only notice on the dipstick tube, but blue smoke will be visible from the engine when driving. Both of these symptoms are also relevant if there's an oil leak. To find out more about the symptoms and common causes of oil leaks, please read our dedicated post. Or, if you're seeking diesel engine part following damages to your current engine parts, please contact our team for assistance. 

Credit to:  MS Motor Service