A Shanghai Passat sedan, as the driver in the process of running water tank water leakage, the owners on the highway did not pay attention to the water temperature and water temperature warning lights, until the engine due to overheating and automatically turn off the fire was found. The car was towed to a highway repair shop to overhaul the engine. Repair finished test, began normal, but not a few days found that the water temperature table indicates the high temperature. In the low speed and parking idling when the pointer into the red zone, high-speed when the pointer is slightly lower, but the water temperature alarm light does not alarm, and the water tank inside the water pressure is high. The owner had to drive more than 100 km to return to the original maintenance, in the two repair process has suspected that the thermostat damage, pump fan speed is not enough, the water temperature sensor failure, pump circulation is insufficient. So the thermostat removed, so that the coolant directly take a large cycle, water pump fan coupling, water temperature sensors and pumps are all replaced with new pieces, the results did not change the temperature is too high.
    At that time the repair shop director, mechanic and so can not find out where the problems, but the repair costs have to take pictures, the owners gradually lost confidence in the plant. We take this car repair, because the pump, water temperature sensor and water tank are new pieces, so do not do the object to deal with suspicion. Will be removed from the car thermostat with boiling water test to confirm the performance is good, and re-installed, the original cooling fan coupling and re-installed and found that the pump fan at high temperatures work properly, check the car ignition timing is good, Acceleration is strong, exhaust is smooth, idling is also very stable. Thus eliminating the lack of ignition due to poor combustion caused by the possibility of high temperature, but also ruled out the exhaust blocked, with the gas timing is not right and the mixture is too thin caused by high temperature. At this point, we will open the expansion of the water tank cover, the rapid acceleration test did not find a bubble generated on the car to check the basic end, but did not find the cause of the malfunction. Because the car is overhaul after the high temperature, therefore, only the disassembly of the engine overhaul, from the inside of the engine to find a direct cause of high temperature. When removing the cylinder head bolts, it was found that there were four cylinder head bolts that were not released at all. After removing the cylinder head, check the screw holes of the four bolts on the cylinder and find that the threads have peeled off and come out of the hole with a screwdriver. As the cylinder price is not low, but also because of the high temperature cylinder and the replacement of the new cylinder, so I decided to consider the interests of owners, no longer replace the cylinder and the use of screw hole repair method. First with the drill bit of these damaged screw holes for reaming, and then tap the tapping, the thread repair sleeve hole, before the assembly and further check the cylinder head, although the cylinder head has a certain deformation, but still have a certain Of the use of value, the use of plane diffraction method to flatten the cylinder head plane, until the flatness of the technical parameters meet the requirements.
Re-install the engine, the cylinder head bolts according to the specified torque tightening, the first screw to 30N · m, the second tightly to 60N · m, the third turn 90 ° turn 90 °. After the engine loading test, on the highway to stop idling, low speed, medium speed, high speed and accelerated deceleration repeated driving test, no overheating phenomenon. At this point, the owner is still not assured, one of the repair shop before he was bitter bitter, the second is the economic loss of serious, the owner made a few days without problems and then checkout. Two days later, due to the car over the bumpy road when the speed is too fast, the tank from the tray within the pine (before the repair shop to remove the tank), the fan fan fan blades sweep. Damaged parts just in the middle of the tank, there are five water grids were sweep bad. At this point, the new trouble came again. We recommend the owner to replace the new water tank, he believes that the tank is a new change, do not agree to change, decided to find someone to repair. The water tank back and found that the middle of the damage to the five water grill are folder flat sealed, the car will drive away, the day the phone is also the water temperature table shows the water temperature is too high. After the car opened to my factory carefully check the hot car when the pump fan speed (with a coupling fan) is running normally. So explained to the owner is due to the middle of the water tank was sealed, no coolant circulation, resulting in water tank heat is not enough to lead to high temperatures.
    Owners think that such a large tank only sealed a few water pipes should not have such a big impact, or the engine is faulty. Really was bitten by a snake, ten years afraid of grass rope. Finally, I plant proposed by us to get a new water tank to the car, if the water temperature returned to normal, the owner had to agree to change the tank, if the water temperature is too high, we admit that the car is still not repaired, the tank can not change. After the new tank load, and test, in a variety of speed under the water temperature are normal, so that the owner is very happy, and agreed to replace the tank. And after a few days of test run, the engine in good condition, the owner admitted that the car has been completely repaired. The car due to coolant leakage, so that the engine serious overheating, excessive expansion caused the engine damage. Can the fixed-point repair shop in the process of overhaul, not only did not carefully repair, and with their own geographical advantages, to deceive customers.
    Tighten the cylinder head bolts with a torque wrench and then recklessly force, so that the cylinder thread thread, resulting in the cylinder head is not tightened. The combustion gas in the cylinder enters the water jacket through the cylinder pad to form the high pressure and high temperature. But because the leakage is very small, the engine work fairly smooth, in the expansion tank can not see the bubble, which to increase the difficulty of judging the fault.
    The second high water temperature is due to tank clogging is not caused by the cycle. From the owner of the driving operation point of view, if any alarm phenomenon occurs, should be dealt with in a timely manner, must not be sick with strong, know the cylinder thread slider, cylinder head bolts torque is insufficient, but not repair. On the contrary, the use of fraudulent means to repair, to pretend to do the real repair, this method of repair in the maintenance sector should really be condemned. But also charged a high maintenance costs, so that customers are very dissatisfied. From the professional ethics, maintenance personnel should always have a scientific and prudent work attitude, like a hospital doctor, the "life and death" in the first place. To establish a good professional ethics, must not follow the "car repair is a means to make money is the purpose of" awareness to operate. On the contrary, if the repair shop in the assembly process found in the new purchase of the cylinder thread slider, cylinder head bolts can not be tightened, take the relevant maintenance measures, can avoid such a ridiculous event. Therefore, also remind the maintenance sector friends can not only consider the interests of the moment and harm customers.