(5) When the newly overhauled engine rotates the crankshaft, the resistance is too large, and the clearance of the main bearing, side rod bearing, camshaft bushing and other accessories is too small. At this time, appropriate running-in process should be adopted for running-in.
Second, the oil pressure is too low. Cause and diagnosis 1. Phenomenon: After the engine is started, the oil pressure quickly drops to zero; When the engine is running, the oil pressure is always too low, and the oil pressure warning light is on; The oil level in the oil pan rises; There is an oil leak. 2. Reason: insufficient oil in the oil pan; Oil viscosity is too small; Insufficient spring force of pressure limiting valve or improper adjustment; Serious oil leakage in the lubrication system pipeline; The secondary oil filter is damaged and leaks oil; Oil pump wear or even failure; Oil pressure gauge or sensor failure; The clearance between the main bearing, connecting rod bearing and camshaft bushing is too large. 3. Diagnosis and Troubleshooting (1) Check the oil level and oil viscosity of the oil pan. Pull out the dipstick for inspection. When the oil level is too low, please replenish oil. When the oil is too thin, it means that the viscosity is too small or the viscosity-temperature characteristics of the oil are too poor, and the oil that meets the standard should be refilled. When the oil has emulsifying phenomenon or water droplets, and the oil level has an upward trend, it means that the coolant leaks into the oil pan. At this time, the leaked parts should be identified and eliminated. (2) Check and maintain the main components of the lubrication system. Remove the lead from the oil pressure sensor, turn on the ignition switch, ground the lead and cylinder block, and observe the state of the oil pressure gauge. If the pointer of the oil pressure gauge quickly rises to the maximum reading, it means that the oil pressure gauge is good; If the pointer does not move or the increase is small, it means that the oil pressure gauge is faulty or the wire is open, and a new oil pressure gauge or wire should be replaced. When the sensor is damaged, it can be replaced with a new sensor. After inspection, the oil pressure gauge, sensor and filter are all free of faults, and when there is no oil leakage in each pipeline of the lubrication system, the oil pump should be removed and the filter cleaned.
(3) When the engine is used for a long time and the matching parts such as bearings are seriously worn, the bearing bush should be replaced again.
3. How to prevent the oil pressure from being too high or too low? Normal oil pressure of automobile engine is the premise and necessary condition to ensure sufficient and good lubrication between engine friction parts. Under normal circumstances, the oil pressure should not be lower than 50kPa when idling; The oil pressure should be kept at about 200-300kPa at medium and high speed. When the engine is running, once there are internal faults, such as excessive engine temperature, increased wear of crankshaft and connecting rod bearing shells or loose fit, it will affect the fluctuation of oil pressure. In many cases, the low engine oil pressure is due to the failure of various components of the engine lubrication system. Once the oil pressure is found to be too low when the car is driving, it should stop to find out the reason, and then drive after it is eliminated. Otherwise, it is easy to cause "bearing" due to low oil pressure, and the engine may be scrapped in severe cases. Therefore, the following points will better prevent the oil pressure from being too low. 1. Check (1) frequently and take out the dipstick to see whether the oil is sufficient, whether there is gasoline or water in the oil, and add or replace the oil if necessary. (2) When the engine is working, carefully check whether each part leaks oil. (3) Check whether the oil pressure sensing plug and oil pressure gauge are normal. Ground the oil sensing plug. If the pointer of the oil pressure gauge swings from 0 o'clock to the bottom, it means that the two are working normally. If the pointer does not move, the sensor plug is damaged and should be replaced. (4) Check the oil pressure of the lubrication system. Unscrew the induction plug and start the engine. At this time, there should be oil gushing out from the screw hole, indicating that the oil pressure of the lubrication system is normal and the fault lies in the induction plug. (5) If the above inspection is still invalid and no fault is found, it is necessary to remove the oil pan, clean the oil filter and the oil filter, and check and adjust the assembly clearance between the crankshaft main bearing and the connecting rod bearing. 2, strict assembly (1) In the maintenance of the engine lubrication system, a little carelessness in assembling parts will cause the phenomenon of low oil pressure. For example, the gasket between oil pump and cylinder, the gasket between oil filter and cylinder, etc. When making these gaskets, the oil hole should have an oil outlet, and a spacer should be left between the oil inlet and the oil outlet. Similarly, when some parts that should not appear are installed incorrectly, the oil pressure will be too low. For example, the newly replaced cylinder block is missing the oil plug head or the oil plug head is not properly assembled.
(2) Crankshaft front and rear oil seals, in automobile use, due to improper assembly method or unreasonable design of crankshaft oil seals and wear of seals during use, oil pressure will be too low and oil will leak. Therefore, in order to prevent the crankshaft oil seal from leaking oil, we should pay attention to two points: first, when the engine is disassembled for inspection, we should replace it with a new oil seal to ensure that the reliability coefficient of the oil seal is at the maximum; Secondly, the packaging of new oil should be carried out in strict accordance with the operation requirements, especially the rear end of crankshaft adopts packing oil seal, and the gap is tight.
Summary: When choosing engine oil, many drivers often only consider its price, but ignore the performance of the engine oil itself, thinking that the quality of the engine oil is similar, which is actually incorrect. Among the characteristics of engine oil, the most important point is its viscosity. At present, the engine oil on the market is divided into mineral oil and synthetic oil, and the highest grade oil belongs to synthetic oil. Generally, high-end cars should choose synthetic engine oil. The viscosity index of synthetic oil is higher than that of ordinary mineral oil, and the viscosity changes little with temperature, so it can still maintain appropriate viscosity and provide appropriate protection under high temperature and cold conditions. In addition, synthetic oil has almost no tendency to produce acid and sludge due to oxidation, so it has a longer service life and can provide proper lubrication and effective protection for the engine under various harsh working conditions. In addition, even the best oil must be replaced after a certain mileage. Because the oil will gradually oxidize during use, the additives inside will gradually disappear.
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