Engine Oil Consumption – Where Does It Go And Why




Engine Oil Consumption - Where Does It Go And Why
Engine Oil Consumption - Where Does It Go And Why

So, engine oil consumption, is now increasing, as the oil change intervals, become higher.

But, most modern engines don’t suffer from, engine oil consumption. That’s why, many vehicle owners, forget to regularly check their levels.

As a result, oil level warning systems are becoming, standard equipment on many vehicles. Most new engines today, use less than half a quart of oil, in 3,000 to 5,000 miles.

Furthermore, some have almost no, engine oil consumption. But, as the miles accumulate, wear and oil consumption naturally go up. So, most of the time, an engine that burns oil will, foul the spark plugs.

Engine Oil Consumption
Fouled Spark Plugs

That, in turn will cause ignition misfires; higher emissions and likely damage the, catalytic converter.

Excessive engine oil consumption, will also shorten the service life of; oxygen sensors and catalytic converters. So, as engines wear the combined loss from, external and internal oil leaks; will just add to the increase of engine oil consumption.

External Oil Consumption Sources:

  • Crankshaft seals
  • Oil pan gasket
  • Timing cover gasket
  • Cylinder head gasket
  • Valve cover gaskets
  • Intake manifold gasket
  • Turbocharger

Internal Oil Consumption Sources:

So, a large puff of blue oil smoke from the exhaust; after an extended idling period; usually indicates internal engine oil consumption.

Some causes may include:

  • Worn piston rings
  • Worn valve seals
  • Leaking, intake manifold gaskets
  • Clogged, oil drain back holes
Engine Oil Consumption
Blue Oil Smoke From The Exhaust

So, How Can Engine Oil Enter The Combustion Chamber ?

Consequently, worn or cracked intake valve stem seals can; leak oil through the, valve guides. Also, the spark plugs might show some oil ash accumulation; on the side of the electrode, facing the intake valves.

Engine Oil Consumption
Worn Or Cracked Intake Valve Stem Seals

Oil leakage through the exhaust valve guides isn’t as common; since normal exhaust flow generates positive pressure. On the other hand, most oil consumption is; through the pistons and piston rings.

Fuel Washed Cylinders

So, there is a condition that contributes to engine oil consumption; generally referred to as “fuel wash“. It is caused by engine flooding; at initial startup or in early operation of a, newly rebuilt engine.

This phenomenon can cause very serious damage to:

Damaged Cylinder Bore
Damaged Cylinder Bore

When flooding occurs from a fuel system malfunction, the excess fuel; washes the oil film from the cylinder walls. As a result, metal to metal contact occurs and scuffing takes place. This condition is similar to and also sometimes referred to as, dry start.

Piston Ring Sealing

Oil washing, is an indication of engine oil passing through the, piston rings. So, to better understand ring related oil consumption; let’s look at piston and piston ring design.

Piston Rings
Piston Rings

For example, many top rings are flat; with a convex or barrel shaped outer edge. That’s why, incorrect ring installation is another source of this problem.

Crankshaft Bearing Clearance And Oil Consumption

So, the piston and cylinder are splash lubricated by; oil passing through the connecting rod bearing and onto, the cylinder wall. As a result, excessive connecting rod bearing clearance affects, oil consumption.

Excessive Bearing Clearance
Excessive Bearing Clearance

And, even more on high mileage or incorrectly rebuilt engines. Furthermore, doubling the connecting rod bearing clearance will; quadruple the oil flow to the piston rings. As a result, dramatically increasing, oil consumption.

Issues With High-Viscosity Engine Oils

So, using high-viscosity oil might prevent low tension piston rings from; contacting the cylinder wall; which can increase oil consumption. Also, engine oil slinging off the crankshaft; not only lubricates the rings but; cools them as well. And, since high viscosity oil reduces oil flow; through the connecting rod bearing; cylinder lubrication and cooling will be, negatively affected.

So, while trying to reduce oil flow to the piston rings; the oil film still has to reach the very top of the cylinder wall. Consequently, high viscosity generic oils; might not adequately lubricate the top and second piston rings; especially during cold startups.

So, the flash point of the oil must be high enough; to resist vaporizing under, high cylinder wall temperatures. Therefore, using non-synthetic base oils in synthetic applications; allows this oil film to be, burned away during combustion.

Engine Oil Consumption
Damaged Piston Ring Groves

In practically all cases, synthetic oils protect the upper cylinder. And, also protects the top and second piston rings from; momentarily micro welding to the cylinder wall; during high load driving conditions. So, as miles accumulate synthetic oils also; keep pistons free of varnish deposits; that can cause low-tension piston rings to; stick in their grooves.

Basic Tips To Follow:

  • All engines consume oil. So, always check the oil level; before the oil is drained. Also, compare the mileage on the odometer, with the mileage on the lube sticker; to estimate the engine’s, oil consumption rate.
  • Oil flows downhill. Use a bright flashlight to examine the engine for leaks. Beginning with the camshaft or rocker arm covers.
  • If there’s oil dripping from the bellhousing area; remember that automatic transmission oil is usually red. However, engine oil is black or brown. So, check the level of both; to help determine the source of the leak.
  • Oil consumption with no apparent oil smoke; often indicates collapsed oil control ring expanders or worn oil control rings.

  • Poor lubrication can cause modern piston rings to; overheat and lose their tension. When combined with excessive varnish; the piston rings can stick, in a collapsed position.
  • Excessive compression ring blow by; will force engine oil into the intake air ducting or intake manifold.
  • Also, a combination of low speed driving and neglected oil changes; on variable displacement engines; can cause the piston rings to stick in their grooves; on the deactivation cylinders.
  • Crusted oil ash deposits on spark plugs and upstream oxygen sensors; are the best indicators of excessive, internal oil consumption.

Conclusion

Preventing engine oil consumption is even more important now. Because, many modern vehicle models come with; extended oil change intervals. So, monitor your engine oil level and condition more frequently; at least once or twice a month. Finally, change the oil as necessary; don’t wait for the manufacturer’s suggested interval.

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