The reason and solution of engine burning oil

The reason and solution of engine burning oil

Different engines have normal oil consumption values, and the normal oil consumption of different engine models is different. The following is a list of the reasons why the engine "burns" the oil, which is used as a reference for the "high oil consumption" and "burning" problems encountered in the maintenance of diesel engines. Green Energy produces, sells, and maintains Jichai 190 series diesel engines, 190 marine engines, and 190 series oilfield drilling equipment.

1. External leakage of engine oil

There are many reasons for oil leakage, including: oil lines, drain ports, oil pan gaskets, valve chamber cover gaskets, oil pump gaskets, fuel pump gaskets, timing chain cover seals and camshaft seals. The above possible leakage factors cannot be ignored, because even a small leakage will cause a large amount of oil consumption. For example, one drop of leakage every 6 seconds means that 0.56 liters of oil is consumed per 100 kilometers. The best way to detect leaks is to place a light-colored cloth on the bottom of the engine and check after starting the engine. The leak location can be judged by the position of the oil drop on the cloth.

2. Front and rear oil seal failure

Damage to the front and rear main bearing oil seals will definitely cause oil leakage. This situation can only be discovered when the engine is running under load. The main bearing oil seal must be replaced after it is worn, because it will cause a high amount of leakage just like the oil leakage.

3. Wear or failure of the main bearing

Worn or faulty main bearings will throw up excess oil and be thrown to the cylinder wall. As bearing wear increases, more oil will be thrown up. For example, if the bearing design clearance of 0.04 mm can provide normal lubrication and cooling functions, if the bearing clearance can be maintained, the amount of oil thrown out is normal, and the bearing will not be damaged. When the gap increases to 0, 08 mm, the amount of oil thrown out will be five times the normal amount. If the gap is increased to 0.16 mm, the amount of oil thrown out will be 25 times the normal amount. If too much oil is thrown out of the main bearing, more oil will be splashed on the cylinder, making the piston and piston ring unable to effectively control the oil. This can cause oil burning or carbon deposits on the piston and piston ring. Generally, if the oil is lost to the main bearing too much, the connecting rod bearing will be short of oil, resulting in insufficient oil splashing on the cylinder wall in some low-speed situations, causing wear of the piston ring and piston, and the engine cannot run at high speed. Time control oil. Therefore, the result of main bearing wear is high oil consumption.

4. The connecting rod bearing is worn or damaged

The effect of connecting rod bearing clearance on oil is similar to that of the main bearing. In addition, the oil is thrown more directly onto the cylinder wall. Worn or damaged connecting rod bearings cause too much oil to be thrown onto the cylinder wall, causing the pistons and piston rings designed to control the normal amount of oil to be unable to effectively control the excessive oil, so that the excess oil enters the combustion chamber and is burned. It means that the oil consumption is high.

Note: Insufficient bearing clearance will not only cause its own wear, but also wear of the piston, piston ring and cylinder wall.

5. The camshaft bearing is worn or damaged

Camshaft bearings are usually pressure lubricated. If the gap is too large, excess oil will leak. The leaked oil will soak the valve guide and valve stem, causing increased oil consumption.

6. Crankshaft journal wear

Worn crankshaft journals have the same effect on oil as bearing wear. When it wears and loses roundness, the gap between them and the round bearing will be uneven. The gap between the out-of-round crankshaft journal and the bearing changes during the rotating motion, which will throw out more oil. The out-of-round bearings need to be reground and matched with smaller bearings.

7. The cylinder liner is ground into a cone or out of round

For cylinder liners that are ground into a slight taper and out of round (decreased cylindricity and concentricity), the oil consumption can be controlled by the piston and piston ring. However, with the continuous increase of cylinder liner taper and out-of-roundness, the control of oil consumption becomes more and more difficult. This is the result of a combination of many factors. As the gap between the piston and the cylinder liner increases, it will cause the piston to swing during operation; this instantaneous tilt and swing will result in excessive oil retention on one side of the piston, and the same situation also occurs on the piston ring. In this way, as the piston continues to swing back and forth, some oil will escape into the combustion chamber. For each revolution of the crankshaft, the piston completes two strokes, one up and down. When the engine is running at 3000 rpm (approximately 60 mph), the piston ring running in the deformed cylinder liner will undergo 6,000 changes in size and shape per minute. As a result, in the case of high-speed operation, the piston ring may not be able to adjust the clearance between itself and the cylinder liner in time (especially when it runs to the wear part of the cylinder liner, the matching gap is too large). Therefore, as long as the above situation occurs, it will cause the engine's oil consumption to be too high.

8. Cylinder liner deformation

Different from the out-of-roundness of the cylinder liner due to wear mentioned in 7, there are other reasons, such as uneven heating or uneven tightening of cylinder head bolts, which may cause the cylinder liner to be twisted and deformed, causing the piston ring to fail. Proper contact is formed with the surface of the cylinder liner, and the oil scraping function is reduced; as a result, excessive oil remains locally, which eventually escapes into the combustion chamber and is burned, resulting in increased oil consumption.

9. "PCV" Crankcase positive pressure ventilation valve or pipe is blocked

The main function of PVC (Crankcase Positive Pressure Ventilation) is to recycle the mixed gas from the engine combustion chamber into the crankcase to reduce the content of unburned hydrocarbons. The blow-in mixed gas is a mixture of air, fuel oil and combustion exhaust gas. During the work stroke, due to the high pressure, it blows into the crankcase through the gap between the piston/piston ring and the cylinder liner. PVC systems usually have a pipe that routes the crankcase to the carburetor or intake manifold. The vacuum generated during the intake of the engine's intake manifold sucks the mixed blow-by gas out of the crankcase, enters the combustion chamber, and is recycled again. The PVC (Crankcase Positive Pressure Ventilation) valve may be blocked by sludge, paint film or other impurities in the mixed blow-by gas. This will cause the engine oil to deteriorate and generate excessive deposits. As a result, the piston ring (oil ring) will be blocked, the oil consumption will increase, and the piston ring will wear prematurely; the crankcase pressure will increase, resulting in the failure of the crankshaft sealing ring, the oil leakage, and the engine work. The situation has deteriorated.

10. Honing abrasive wear

If the cylinder liner is honed or polished, it must be cleaned strictly as required to prevent residual metal chips or abrasives from damaging the surface of the piston ring groove. The cleaning method is as follows: After honing, you must thoroughly clean the cylinder liner with a brush dipped in soapy water, and then apply oil immediately; or use 10# lubricant to clean the cylinder wall and carefully wipe it clean. Repeat the above process until all foreign objects are removed. No matter which method is used, the final inspection is required: wipe the surface of the cylinder liner with a white cloth. If the white cloth is still clean after wiping, it indicates that the cylinder liner has been cleaned.

Note: Do not use gasoline or kerosene to clean the honed cylinder wall. Because they cannot remove the abrasive adhering to the cylinder wall, and will bring it into the pores of the honing pattern. Therefore, cylinder liners that have not been cleaned normally may cause premature wear, piston ring failure, and ultimately increase oil consumption.

11. Piston ring groove wear

Whether the end surface of the piston ring groove is flat or not, and whether the gap between the piston ring and the piston ring groove is correct or not, is an important factor in whether the piston ring can play a good sealing effect. Generally, the side clearance of the piston ring groove of an automobile engine cannot exceed 0.002"-0.004". When the piston moves up and down, the piston ring must fit properly in the piston ring groove. If the piston ring groove is deformed, the piston ring will not work properly and the oil will escape into the combustion chamber. The worn piston ring groove will increase the side clearance, causing excessive oil to escape into the combustion chamber. Conversely, too large side clearance will cause the piston ring to hit the piston ring groove, causing further wear of the piston ring groove. If the situation is not improved, it may even cause the piston ring bank to break.

12. The piston ring bank is damaged or chipped

The damage or fragmentation of the piston ring land causes the piston ring to be unable to be properly embedded in the piston ring groove, causing excessive oil to escape into the combustion chamber. In addition, it will cause complete damage to the cylinder liner, piston and piston ring. So pay close attention to it. Once there are signs of this, it must be replaced immediately.

13. Wear of valve stem or duct

If the valve stem and the duct are worn out, the vacuum suction generated during the intake will draw the oil and oil vapor between the valve stem and the duct into the intake manifold, and finally enter the combustion chamber and burn it. If this situation cannot be improved, when the engine is replaced with a new piston ring, the oil consumption will increase due to the increase in intake vacuum suction; when the engine is overhauled, it was originally attached to the valve stem and duct surface After the sludge and other sediments are removed, the gap will further increase, and the oil leakage loss will become more obvious. For overhead-valve engines, whether it is an exhaust valve or an intake valve, oil loss may occur. The problem of high oil consumption caused by excessive valve guide clearance can be improved by continuously trimming the valve stem. Sometimes new valves also need to be trimmed in this way. Adopting advanced integrally fastened type valve oil seal (Bonded Valve Seal) can effectively prevent oil leakage and loss.

14. Bending deformation of connecting rod

A bent connecting rod will cause the piston to fail to run in a straight line along the cylinder liner, which will affect the normal sealing function of the piston ring and increase oil consumption. In addition, the bent connecting rod will also cause the gap between the connecting rod bearing and the piston pin to change, causing premature wear of the connecting rod bearing and causing more oil to be thrown onto the cylinder wall.

15. Piston pin wear or improper position

If the piston pin is worn or improperly assembled, the oil flowing to the piston pin under pressure will be thrown onto the cylinder wall, and the piston ring cannot scrape off the excess oil. This not only leads to direct excessive oil loss, but also the formation of carbon deposits will block the oil passage and cause the piston ring to seize.

16. Piston pin assembly is too tight

If the two ends of the piston pin are assembled too tightly, the piston will not be able to expand and contract normally under the repeated hot and cold working environment of the engine, which will cause the piston to deform, and then the cylinder wall will be scratched, which will inevitably lead to downward blow-by. And excessive oil consumption.

17, the oil circuit is blocked

After long-term operation of the engine under severe working conditions, the carbon deposits and foreign matter produced can easily block the oil passages in the piston and piston ring. At this time, the oil cannot return to the crankcase in the normal way, but stays in certain parts such as valve guides, resulting in increased oil consumption. If the oil passage in the connecting rod or other parts is blocked, it will lead to poor lubrication of the engine, increased wear and oil consumption. In order to avoid the occurrence of the above situation, prevention should be carried out in accordance with item 28. Of course, there is no need to reserve a side gap for this.

18. Unbalanced torque of main bearing cap bolts or connecting rod bolts

If the torque of the main bearing cap bolts or connecting rod bolts is unbalanced, the bearing will be out of round and deformed, reducing the service life of the bearing, and causing excessive oil to be thrown out of the bearing. Its influence on the oil consumption is as described in items 3 and 4. Narrated. When installing the bearing cap bolts, a torque wrench must be used and tightened strictly according to the manufacturer's required torque. If the connecting rod bolt torque is not balanced, it will cause the connecting rod to deform, and the consequences are as described in item 14.

19. Unbalanced torque of cylinder head bolts

The stress caused by the unbalanced torque of the cylinder head bolts will cause serious deformation of the cylinder and cause oil blow-by as described in items 7 and 8. When installing the cylinder head bolts, a torque wrench must be used and tightened in strict accordance with the manufacturer's required torque and sequence.

20. Dust and dirty cooling system

Rust particles, scale, deposits or other products in the water jacket and radiator, as well as the corrosion of the water pipeline, all negatively affect the cooling efficiency of the cooling system. The cylinder deformation caused by this will directly cause oil loss, the reasons are as #7 and #8. The defects of the cooling system cause the engine to overheat, and some cylinders may have local overheating areas, which in turn will cause scratches and adhesions of the cylinders, pistons and piston rings, leading to increased fuel consumption. The overheated engine and the overall oil temperature of the oil pan will also cause fuel consumption to increase.

21, dirty oil

If the oil is not changed according to the oil change interval, improper maintenance of the oil filter will cause the oil to become dirty, causing the oil to block the oil gaps at the piston and piston ring, resulting in increased oil consumption as described in cause #17. Dirty oil can also cause increased wear of bearings, cylinders, pistons, and piston rings. These worn parts, as explained in the previous corresponding articles, will cause fuel consumption to increase. Special attention: the consumption of dirty oil itself is higher than that of clean oil.

22. Too much oil in the oil pan

Because the oil dipstick was inserted incorrectly and failed to seat to the end, the measured oil level was lower than the actual oil level. Therefore, new oil was added, which made the oil level too high. If the bottom end of the connecting rod of the high pressure lubricated engine touches the oil surface, or the oil ring of the splash lubricated engine is immersed too deep into the oil pool, it will cause excessive oil to be thrown to the cylinder wall and into the combustion chamber.

23. The piston ring is not suitable for engine type or working type

If an improperly sized piston ring is selected (for example, a 0.020” enlarged piston ring is used in a 0.040” enlarged cylinder), the oil on the upper part of the cylinder cannot be scraped back due to improper matching of the two, which will cause immediate damage Oil channeling phenomenon. Similarly, the gap between the piston ring bottom and the ring groove is also enlarged, which further increases oil consumption. The reason is as described in #26. Different types of engines and different working conditions require a variety of specially designed and manufactured piston ring sets. Each type of piston ring set is made for a specific purpose. If it is used in the wrong place, the engine's oil consumption cannot be controlled. It is very important to use the correct piston ring set.

24. High engine vacuum

The increase in speed, valve overlap angle, and compression characteristics of modern engines has increased the engine's vacuum. When some new engines slow down, the suction vacuum is as high as 25 inches (635mm) Hg (old engine design = 508mm Hg). High vacuum requires the development of a new oil ring to effectively seal both sides (upper and lower) of the piston ring groove to avoid oil leakage from both sides and back of the oil ring during high vacuum and deceleration. This reason is often a major cause of blue smoke or high fuel consumption. Therefore, when necessary, it is important to use an oil ring with side sealing capabilities.

25. Timing gear or chain wear

The wear of the timing gear or chain will cause the timing of the valve and crankshaft to be out of sync. Due to the excessive backlash caused by the wear of the gear teeth or the chain, the adjustment of the engine cannot be realized: the timing of the previous lap may be different from the timing of the next lap. When the movement of the valve and the piston is not synchronized, it will cause excessive oil consumption. The reason is that the excessive vacuum in the combustion chamber will draw in a large amount of oil and burn it.

26. When the piston ring is installed, the clearance on the circumferential end surface is too small

When installing a new piston ring, it must be noted that at the smallest diameter of the cylinder, the piston ring still has enough circumferential end clearance to compensate for thermal expansion. Generally, the clearance required for the cast iron ring of the vehicle engine is 0.003-0.005 inch/inch bore. As it directly bears the combustion gas coming from the combustion chamber, the heating rate and working temperature of the piston ring are higher than those of the cylinder. The cylinder wall has a lower temperature due to the action of the water jacket. This means that the piston ring expands more, so there must be a gap to compensate-that is, the circumferential end face gap-otherwise, the end face of the piston ring will interfere with the cylinder wall during engine operation, impact, and cause abrasion, adhesive wear, and lead to Fuel consumption rises. If the engine continues to run, especially when the load is heavy, the adhesive wear will be more serious. The end face of the piston ring is pressed inward toward the piston ring groove, and the gap between the ring and the cylinder wall is enlarged. The high-temperature and high-pressure combustion gas in the combustion chamber directly burns the lubricating oil on the cylinder wall along this passage, and the blow-by gas enters the oil bottom, which greatly increases Oil consumption. Severe interference can even cause the fracture of the piston ring, and the consequences are as described in #27.

Excessive clearance of the circumferential end face of the piston ring will also increase oil consumption.

27. Worn or broken piston ring

If the piston ring is broken or excessively worn, causing the pressure stress and gap to be unable to maintain, excessive oil will be sucked into the combustion chamber during the suction stroke, and the combustion gas will move down the piston during the power stroke. Both of them cause the combustion and carbonization of the oil at the piston, cylinder wall, and piston ring. The broken piston ring is more destructive, and the broken pieces with sharp mouths are likely to cut into the side of the piston ring groove, causing the destruction of the land and the complete damage of the piston. When the engine is overhauled, the worn piston ring should be replaced immediately instead of being reused. The new piston ring has a quick positioning surface, which can control oil consumption immediately. The used piston ring, even if it is only slightly worn, cannot be properly positioned due to the polished surface, which will also cause excessive oil consumption.

28. Piston ring sticky ring

Obviously, the piston ring of the sticky ring cannot control the oil. Therefore, this situation should be avoided as much as possible. First of all, the installation of the piston ring should ensure the correct piston ring backlash, so that when the engine is working, the piston ring can still move in the ring groove at the operating temperature. In addition, ensure that all parts of the engine are clean and free of dust particles when installing the piston ring, otherwise, the piston ring may stick. Third, select oils with excellent performance to reduce the formation of carbon deposits, sludge, and paint film. Fourth, the oil should be changed regularly and the oil filter should be cleaned. Fifth, avoid overheating of the engine.

29, the valve timing is lagging

The lagging valve timing causes the intake valve to close for too long after the start of the intake stroke, and the vacuum in the cylinder rises, which increases the probability that the oil is sucked into the combustion chamber of the upper cylinder from the piston and ring, and the cylinder liner gap.

30. The oil pressure is too high

Incorrect setting of oil pressure and failure of safety relief valve will cause excessive oil pressure. The result is that the engine is wetted with excessive oil, which produces the same result as bearing wear.

31. Oil viscosity

The viscosity of the oil used is too thin, which may cause high oil consumption. Please refer to the vehicle maintenance manual to select the appropriate oil viscosity according to the driving conditions and ambient temperature.

32. Piston design

Some of the latest engines have adopted a new piston ring design in order to meet emission requirements. Sometimes, this design will have a slight "knock" at startup. Sometimes this will increase oil consumption.

33. Broken inner gasket/air inlet

In the new engine design, various composite materials composed of metals and other materials are often used. Due to the difference in the degree of thermal expansion and contraction of different materials, thermal stress fatigue or cracking will occur in the packing and seal after long-term operation, which also leads to Fuel consumption levels have risen.

34, pre-ignition knock

Most new engines are equipped with knock sensors to adjust the timing system to reduce emissions and improve engine power and performance. Pre-ignition knocking is caused by the pre-ignition of fuel during the combustion process. Pre-ignition leads to a sharp increase in the pressure accumulated on the piston, disrupting the normal movement of the piston ring, causing the seal on the top and bottom sides of the piston ring to fail, and ultimately causing blow-by gas and fuel consumption through the piston ring to increase. The failure of the intake air flow sensor and the failure of the throttle position sensor can also cause the same problem.

35. Modifications and spare parts used by users to improve engine performance

Adding modified parts to improve engine performance/power in inventory or in-use engines increases the possibility of high fuel consumption of the engine.

36, engine lugging

Lugging refers to letting the engine run at a low speed when high speed (more power/torque) should be used, which will cause the piston to bear more pressure and increase oil consumption.

37. Improper overspeed operation

There are many different reasons related to causing the engine to run over speed when it is not suitable for overspeed running, all of which will lead to an increase in engine fuel consumption. These situations include crawling and frequent start-stops in urban traffic. You can also refer to Cause 36.

38, turbocharger seal leakage

The seal leakage of the turbocharger will suck the oil into the combustion chamber, burn it there and form carbon deposits, hinder the normal operation of the engine, and further lead to more oil consumption.

39. High intake resistance

Too high resistance of the intake system will increase the vacuum in the engine and increase the oil consumption, as described in item 24. A severely clogged air filter is an example of this situation.

40. Fuel dilution

If the fuel that is not completely burned enters the lubrication system, the oil will become thinner and more volatile, which will lead to higher oil consumption. Excessive fuel may enter the lubrication system and mix with the oil due to leaking fuel nozzles, problematic fuel pumps, high air intake resistance, or excessive idling.