Engine oil is the lifeblood of an engine. Run out of oil, for just a few seconds, and the engine will be destroyed. With extended oil changes, oil loss is on the increase and not checking the oil level may lead to major problems.
Every month, a surprising number of clients bring their vehicles to us, with engines that are destroyed from lack of oil. The results are catastrophic and engine replacement is usually necessary. This type of expensive damage is often preventable, by routinely checking the engine oil.
Many engines lose oil over a period of miles. Oil loss, of about one quart every two-thousand miles, is considered normal for some vehicles. With three-thousand-mile oil changes this was rarely a problem. With longer oil change intervals, this can be a major issue. In eight-thousand miles such an engine could run out of oil, if it is not checked and replenished.
There are two primary reasons an engine loses oil
Oil Leakage
As oil ages, the additives that help to keep seals pliable are loss. Seals and gaskets shrink, get hard and start to leak. Small oil leaks cause problems but rarely account for much oil loss. Valve cover gaskets, timing covers, drain plugs and seals are all prone to leakage. These leaks often cause a burning odor and can make a mess. The amount of oil loss is relatively small with leaks of this nature.
Large leaks often come from pressurized areas of the engine. Oil pressure switches, oil filters that are loose, rear main seals and head gaskets can cause considerable loss. Sometimes oil is blown under the vehicle by the air current. This may make the leak less noticeable, as there may not be a puddle under the engine.
The positive crankcase ventilation or PCV system attempts to maintain a slight negative pressure on the engine. If this system fails, pressure can blow seals and gaskets out. Sludge buildup, from infrequent oil changes, can plug this system. At the same time, seals are not being protected, and major oil leaks often result. Frequent oil changes are the best prevention against these problems.
Oil Consumption
Loss oil that is not leaking is being consumed within the engine. With older vehicles this was typically accompanied with a puff of smoke from the exhaust. With modern vehicles, the catalytic converter usually prevents smoke. Smoke in the exhaust is vaporized by the converter. Unfortunately, this may drastically raise the temperature and damage the converter, over time.
Pistons are sealed to the cylinder by steel rings. These rings ride on a very thin film of oil, which prevents cylinder wear. Without this film of oil the engine would wear very quickly, and power would be reduced, due to friction. Dirty oil protects the cylinder a lot less than fresh oil. Heat and pressure cause the viscosity of oil to break down over time. Before this happens, the oil must be replaced.
Piston rings are made in different styles, depending on their applications. Most engines use three piston rings, though some use more. The ring farthest from the combustion chamber is the oil ring. The oil ring is normal composed of several pieces and designed to scrape most engine oil from the cylinder wall. Oil passes through the oil ring, and openings in the piston, and returns to the crankcase. A very small amount of oil is allowed to remain, and lubricates the upper rings.
The upper piston rings seal compression from the combustion chamber and also control oil. The middle ring has a scraper built in and leaves almost no oil behind. What little oil remains, stays between the upper rings and serves as lubrication.
With extended oil changes, viscosity may suffer and rings can stick in the piston grooves. When this happens, oil passes by the rings and is drawn into the combustion chamber and is burned. Pistons move up and down the cylinder about 2,000 to 4,000 times per minute, so a considerable amount of oil may be lost.
One method of checking worn and stuck rings is, with a compression test. A pressure gauge is inserted in place of the spark plug. The engine is then cranked with the starter, and the pressure in the cylinder is measured. Cylinder pressure should normally run 150 to 250 PSI per cylinder, in a gasoline engine.
If the cylinder pressure is low, a small amount of light oil is added to the cylinder, and the test is repeated. This oil will temporarily seal the piston rings and cause the pressure to rise. A significant rise (15 or more PSI) signals a problem with the piston rings.
Sometimes,stuckpistonringscanbefreedwitha professional chemicaltreatment.Thisisaprofessionallyadministeredcombinationofcleanersandsolventsaddedtotheengineoil,combustionchamberandthroughthe intake. Over the counter oil additives will not work and may cause harm. Even with a professional treatment, ifringsareworn,brokenorseverelystuck,thechemicaltreatmentwillnothelp.
Valve guide seals
Valves pass through the cylinder and seal the combustion chamber. The area where the valves exit the top of the head is sealed by a valve guide seal.
On the intake stroke, there is a vacuum created at the base of the intake valves. The valve cover is full of oil, used for camshaft and valve lubrication. If the valve guide seals are worn or have become hard, oil will be drawn down the valve stem. This oil is burned in the combustion chamber, much like oil passing the rings.
Sludge in an engine may restrict the drain back holes in the cylinder head. This allows more oil to remain in the area and makes the problem worse. Wear in the valve guides, allows the valve stem to move, and makes oil even more difficult to control.
Valve guide seals can often be replaced, without removing the cylinder head. Special tools are available to pressurize the cylinder with air. This pressure holds the valves up, while other tools remove the valve springs. After removing the valve springs and retainers, the seals may be replaced, and the engine is reassembled. If the valve guides are not badly worn, replacing the seals often helps control oil loss.
A persistent myth about oil consumption
When an engine starts to consume oil, many people are [wrongly] given the advice, to switch to a thicker or higher viscosity oil. Oil thicker than specified for a vehicle, will not help oil consumption, may make it worse and cause other problems.
Long ago, engines used soft babbitt bearings that would wear and lower oil pressure. Thicker oil would temporarily raise the pressure and perhaps caused the myth. Today this is not a problem. Increasing oil pressure sends more oil to the top end of the engine. This will increase oil on the valve guide seals and may increase consumption.
In an engine with sludge buildup, drain back holes may be partially blocked. Thicker oil will have a more difficult time returning to the oil pan. If oil in the pan runs low, the engine may burn up. Thicker oil will NOT help oil consumption and may make it worse.
Preventing oil loss problems
Most oil loss problems can be prevented with consistent, frequent high-quality oil changes. Extended oil changes allow seals and gaskets to harden. Depleted oil does not protect piston rings and allows them to stick in the pistons. Sludge buildup in the engine may make any of these problems far worse.
Improperly replacing an air filter and cheap filters that do not fit, allows dust to enter the cylinders. Fine dust particles cause extreme wear and damage piston rings. Dirty and substandard fuel has much the same affect.
When oil consumption becomes excessive, rebuilding or replacing the engine is the only cure. This is expensive and very often is preventable.
Check engine oil level regularly
Use high-quality oil and replace regularly
Do not change oil brands, additives may be incompatible
Use only high-quality oil, air and fuel filters
Do not use higher viscosity oil
More frequent oil changes may help oil consumption
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Check engine oil level regularly 
Do not change oil brands, additives may be incompatible