Increased oil consumption

Our mixed vehicle fleet includes large lorries and transporters but also a few cars. We carry out oil changes in our own workshop. Although we do not neglect scheduled maintenance, we always have problems with oil consumption. Several times when the oil level warning light lit up, it was dangerously low. Is our workshop working incorrectly? And why do modern engines even consume oil?


Table of contents

  1. OELCHECK answers:
  2. Causes
    1. Unadjusted oil change intervals
    2. Consumption of dirt-carrying additives
    3. Insufficient piston ring sealing
  3. Oil shrinkage due to loss
    1. Extremely increased oil pressure
    2. Seal failure


Usage conditions and driving behaviour

Full throttle, use which is predominantly of a „stop and go“ nature, or demanding hill ascents cause temperatures and therefore loss due to evaporation to rise.

Oil level in the engine which is too high

For quantities of oil which are too great or if there is too much fuel in the oil due to constant short trips, the crankshaft will dip into the oil sump. But if too much oil is used, increased splashing and therefore more flexing work is the result. As a result, the oil temperature increases.

Incorrect oil quality

It is not without good reason that automobile manufacturers include the ACEA or API specifications of the oils in their operating manuals, or freely share their names. If the specific requirements are not adhered to, e.g. with regard to loss due to evaporation, there is a risk of increased oil consumption. If engine oils are used which are not freely shared, the limit values for exhaust emissions can often not be complied with. Engines of generations Euro V and VI with their complicated exhaust gas treatment systems are particularly affected. Their function is reduced and there is a threat of damage and significantly shorter service lives.

Unadjusted oil change intervals

If oil analyses are not carried out, the oil change intervals stated by the manufacturer or those indicated by the on-board computer should generally be adhered to. In extreme usage conditions, an analysis of the used oil can show that the intervals should be reduced.

Faults in the injection system or valve control

Moving parts of an injection system are partly lubricated via the engine‘s oil circuit. If internal leaks occur, oil can come into contact with fuel in the engine‘s combustion chamber. Even if the exhaust valves open while there is still oil on the wall of the cylinder, partly unburned oil can escape through the exhaust system. This often leads to an increased burden on the exhaust treatment systems. If the number of soot particles in the oil increases due to faults in the injection system or as a result of incorrect valve control, the additives will no longer be able to keep all of the particles in check. The anti-redeposition power of the engine oil decreases, and the danger of deposits increases. The viscosity of the engine oil will also increase, thickening and losing volume. Fail-safe lubrication can no longer be guaranteed, particularly during a cold-start. Fuel consumption rises simultaneously.

Consumption of dirt-carrying additives

All types of engine oil take on a darker colouring after a short while. Their detergent/dispersant additives prevent the formation of sludge and lacquer-like deposits which develop in the form of soot, the products of acid reactions, nitrous gases, unburned fuel residues and water. Dirt is broken down into small particles, suspended in an emulsion and transported to the filter. In this way, the oil ensures the engine is clean and ensures optimal combustion. But there will eventually come a point when the supply of these additives runs out. The anti-redeposition power of the engine oil depletes, and the danger of deposits increases. Fail-safe lubrication can no longer be guaranteed, particularly during a cold-start. Fuel consumption simultaneously rises.

Insufficient piston ring sealing

If worn or broken piston rings do not seal the cylinder piston sufficiently, or if deposits have formed around the oil scraper ring, oil consumption can increase, since the oil which is not scraped off the piston wall and into the oil sump will burn.

Oil shrinkage due to loss

Extremely increased oil pressure

If an oil leakage becomes visible on multiple seals and connection points in the oil circuit at the same time, the cause may be oil pressure which has increased severely. This is not indicated by a warning light and can be caused by deposits in pipes, filters, one-way valves and crankcase ventilation, or by a viscosity that is incorrect or too high.

Seal failure

Modern sealing materials work with the highest precision. If leaks do occur, however, it is often not a material fault, but some other kind of fault. Even a small foreign body, e.g. particles of paint, rust, or the remains of a sealant can interfere with the seal and prevent it from functioning correctly. The same applies to damaged component surfaces. If they are not flat, or are scratched or partially corroded, even the best seal cannot cancel out these defects. If the correct functioning of the seal is interfered with, coolant or engine oil could escape, depending on its position, or a component could become damaged.

Caution should be taken when using liquid or permanently elastic sealants. They can generally only be used on areas that they were designed for. Leaks can pose a threat if sealants have not been tested on the respective oil type, or if sealants are to replace common solid seals.


OELCHECKER Winter 2015, page 8