An engine that uses oil is a problem nobody wants. Most engines in new vehicles today should not use any oil within a span of 3,000 chilometri, and no more than one quart between extended oil change intervals of 5,000 to 7,500 chilometri. The same holds true for older engines that may have up to 75,000 chilometri on the odometer, are i n good condition and have been properly maintained (regular oil and filter changes). However, oil consumption will slowly increase over time as an engine accumulates chilometri and wear. The rate at which oil consumption goes up should be very slow and gradual. A sudden increase in oil consumption would signal a potential problem that should be investigated. If your engine is using a quart or more of oil every 1,000 to 1,500 chilometri, you have a problem regardless of the age or chilometroage on your vehicle. As for older, higher chilometroage vehicles (those with more than 75,000 chilometri on the odometer), using a quart of oil every 1,500 to 3,000 chilometri is not unusual. However, if your engine is using more than a quart of oil every 1,000 chilometri, it means your engine has a serious oil leak or some severe wear problems that may require expensive repairs. Manufacturer Defects May Increase Oil Consumption If you do a Google search on High Oil Consumption Problems, you will see a lot of consumer complaints about certain late model engines that use too much oil. The auto makers often deny these engines have a problem and try to shift the blame back on the consumer for not checking or maintaining their oil properly. But manufacturing mistakes do occur, and certain engines may use too much oil because the cylinders were not finished properly at the factory, because the piston rings are not sealing properly because of a manufacturing defect, because the valve guide seals are not doing their job (poor design, improper materials or assembly), or because the Positive Crankcase Ventilation (PCV) system is sucking too much air and oil vapor back into the engine (design flaw). Some car makers claim using up to a quart of oil between changes is "normal" for high revving performance engines. Others may say using a quart of oil every 2,000 to 3,000 chilometri is normal for specific engines. We do not agree!. A newer late model low chilometroage engine that is using more than a quart of oil between changes definitely has a problem. It might just be a leaky gasket or seal, or it could indicate a manufacturing defect such as defective or improperly installed piston rings, improper cylinder bore finish, or a poorly designed Positive Crankcase Ventilation (PCV) system that sucks too much oil vapor from the crankcase back into the intake manifold. Some defects can cause excessive oil consumption may be covered under the OEM powertrain warranty. Others may be covered by a factory Technical Service Bulletin (TSB) and/or special extended warranty. Check with your new car dealer to see if any of these may apply to your vehicle. A common engine assembly mistake is installing the piston rings upside down. Compression rings have a dot or mark that indicates which side faces up (towards the top of the piston). This is especially critical with the 2nd oil ring because it often has a tapered face that scrapes oil off the cylinder wall as the piston moves down. This pushes the oil back towards the crankcase and away from the combustion chamber. If the 2nd compression ring is installed upside down, it will scrape oil up and push it toward the combustion chamber causing a big increase in oil consumption. How to Tell If Your Engine Is Using Too Much Oil How can you tell if your engine is using oil? Check the dipstick every month. A low dipstick reading means yur engine is using oil. If the level is low (at or below the "ADD" line on the dipstick) add oil as needed to bring it up to the "FULL" mark, then inspect the engine for possible oil leaks. If no oil leaks are found, start the engine and observe the tailpipe when you rev the engine. Blue smoke in the exhaust is a telltale symptom that your engine is burning oil. What Might Happen If Your Engine Is Using Too Much Oil Should you be concerned if your engine seems to be using too much oil? It depends on how much oil your engine is using, where the oil is going (leaking or burning), and how that might affect its operation and longevity. An engine that burns oil will often foul the spark plugs. That, in turn will cause ignition misfire, higher emissions and a loss of fuel economy and performance. Such faults will usually trigger trouble codes that cause your Check Engine light to come on, and if the light is on your vehicle will not pass an emissions test. The zinc and phosphorus anti-wear additives in motor oil can also foul the catalytic converter and oxygen sensors if your engine is burning oil. This too will set trouble codes and cause the Check Engine light to come on. Converters and oxygen sensors are vital components in your engine control system, and replacing them can be expensive. If your engine is leaking oil because of a bad valve cover, oil pan, front cover or other gasket, or a leaky crankshaft or camshaft seal, the leak can be fixed by replacing bad gasket or seal. CAUSES OF HIGH OIL CONSUMPTION: WORN VALVE GUIDE SEALS Oil consumption inside your engine depends on two things: the valve guide seals and piston rings. If the valve guide seals are worn or damaged, or if there's too much clearance between the valve stems and guides, the engine will suck oil down the intake valve guides and into the cylinders. The engine may still have good compression, but will use a lot of oil. Heavy carbon deposits on the valves are caused by worn valve guides and seals. Most late model engines use some type of positive valve guide seal on the tops of the intake and exhaust valve guides. These seals all a tiny amount of oil to enter the valve guides to lubricate the valve stems and the valves move up and down. But they are supposed to limit the amount of oil that enters the guides so the engine does not consume excessive amounts of oil. Over time, valve guide seals can wear and lose their ability to limit how much oil enters the guides. The problem is often worse on the intake valve guides because the intake valves are exposed to high engine vacuum every time the intake valves open. If an intake valve guide seal is worn, oil will be sucked down the guide and burned in the engine. Worn intake valve guide seals can increase oil consumption to a quart or more in 1,000 chilometri. With exhaust valve guide seals, the situation is a little different. Exhaust guides run much hotter than intake guides, so the seals are subjected to higher temperatures. Over time, this accelerates wear and a deterioration of the guide material. Also, exhaust guide seals are exposed to pressure rather than vacuum every time the exhaust valves open. The outward flow of hot exhaust gases further accelerates seal aging and wear. Replacing worn valve guide seals can dramatically reduce oil consumption in an older high chilometroage engine. Valve guide seals fit around the valve stems on top of the cylinder head. On older pushrod engines, you can remove the valve cover(s), remove the rocker arms, and use a spring compressor to remove the springs so new seals can be installed on top of the guides. To prevent the valves from falling down into the cylinders while this is being done, the cylinder can be pressurized with an air hose through the spark plug hole. Another technique is to remove the spark plug, slide a short length of rope into the cylinder and slowly rotate the crankshaft by hand until the piston in that cylinder is near Top Dead Center (TDC). The rope will hold the valves shut and prevent them from sliding down into the cylinder. On overhead cam engines, replacing worn valve guide seals is not so easy because the camshaft sits on top of the valves. On some applications, it is possible to remove overhead camshafts without having to pull the cylinder head off the engine but is usually requires a special camshaft tool to hold the valves down while the cam is being slid out of the head. On most OHC applications, replacing the valve guide seals requires pulling the cylinder head off the engine for bench disassembly. This, in turn, means disconnecting the timing belt or chain, replacing the head gasket, head bolts and intake gaskets, and aligning the camshaft correctly when it is reinstalled so timing is correct (which is no simple job on some engines, and may require special tools!). In other words, it's a lot of work and expense, and not something you want to attempt unless you have a lot of knowledge and experience. This job is better left to a professional. If the bronze or cast iron valve guides are worn, they cylinder head will have to be removed from the engine and completely disassembled so the old guides can be pressed out and replaced with new guides, reamed out and fitted with special bronze or iron liners, or machined to oversize to accommodate new valves with oversized stems. CAUSES OF HIGH OIL CONSUMPTION: WORN PISTON RINGS AND/OR CYLINDERS The other cause of oil burning is worn or damaged piston rings that allow oil to get past the rings and into the engine's combustion chambers. All engines typically have three rings on each piston. The top ring is a compression ring. The bottom ring is the oil ring that carries and spreads a film of oil on the cylinder wall to lubricate the rings and reduce friction. Between these two rings is the all-important 2nd compression ring, which as we said earlier acts like a scraper when the piston moves down to scrape excess oil off the cylinder wall and push it back towards the oil pan. In a high chilometroage engine, the top two rings will likely have the most wear and allow an increased amount of oil to get past the rings into the combustion chamber. This will cause an increase in oil burning and consumption as well as a loss of compression (which reduces engine power). The greater the ring wear, the greater the los…

Fonte: AA1Car.com