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.
Actually, 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.
As a result, causing 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
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
How Can Engine Oil, Enter The Combustion Chamber ?
So, worn or cracked intake valve stem seals, can let oil leak through the valve guides. As a result, the spark plugs might show some, oil ash accumulation; on the side of the electrode, facing the intake valves.
However, oil leakage through the exhaust valve guides isn’t as common. Because, normal exhaust flow, generates positive pressure.
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:
- Cylinder bores
- Piston rings
- Engine Bearings
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.
Piston Ring Sealing
Oil washing, is an indication of engine oil passing through, the piston rings.
Consequently, incorrect ring installation, is another source of this problem. For example, many top rings are flat, with a convex or barrel shaped outer edge. Making it confusing, for some installers.
Crankshaft Bearing Clearance And Oil Consumption
So, the piston and cylinder wall are splash lubricated. Consequently, by oil passing through the connecting rod bearing and onto the cylinder wall. As a result, excessive connecting rod bearing clearance affects, oil consumption.
Consequently, 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. As a result, increasing oil consumption. In addition, engine oil slinging off the crankshaft, not only lubricates the rings, but cools them as well. Because, 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.
In addition, the flash point of the oil, must be high enough, to resist vaporizing under, high cylinder wall temperatures. To clarify, using non-synthetic base oils, in synthetic applications; allows this oil film to be, burned away during combustion.
In practically all cases, synthetic oils, protect the upper cylinder. 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 some oil. First, always check the oil level, before the oil is drained. Next, 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 deactivated cylinders.
- Crusted oil ash deposits on spark plugs and upstream oxygen sensors; are the best indicators of excessive, internal oil consumption.
So, preventing engine oil consumption, is even more important today. Because, many modern vehicle models come with, extended oil change intervals. So, monitor your engine oil level and condition more frequently. Finally, change the oil as necessary, don’t wait for the manufacturer’s suggested interval.
Thank You !