A 1997 Honda Mile 3.0L sedan, using V6 engine, mileage has reached more than 20 million km, the recent vehicle in the process of running, the engine has a coolant temperature is too high or even "boil" failure. Due to the driver's negligence, the vehicle in the case of high temperature engine also continue to drive, eventually leading to the vehicle flame and can not continue to drive.
    Dragged back to the factory, the maintenance staff intuitively checked and found the rear of the engine warm water pipe rupture, resulting in a large number of coolant loss, causing the engine coolant temperature is too high, at the same time found that the radiator water pipe is also aging leakage phenomenon. When we want to replace its water pipes, while unplugging the water pipe, found in the coolant out of the light yellow oil and water mixture. According to conventional experience, this engine due to high temperature and the driver also continue to drive the vehicle at high temperatures, causing the possibility of damage to the cylinder pad the largest. So the maintenance staff will be left and right side of the engine cylinder head removed, clean up the cooling system of water pipes, cylinder water jacket, cylinder head water jacket and water tank in the oil and water mixture, while replacing the rupture of the two pipes, and other aging Of the warm water pipes are also replaced, fitted with cylinder pad and cylinder head, the engine installed complex. The starting engine is running well. The road test engine coolant temperature is normal, then finished delivery.
    But did not last long, the vehicle in half a month after the factory rework. According to the owner to reflect the car back to the back, did not travel how many miles, only driving more than 500 km, the engine coolant temperature is too high. Into the workshop, the maintenance staff of the car were checked, the engine coolant temperature has reached the "boil" level. With the fault diagnosis instrument PGM detection, the engine coolant temperature between 98 ~ 100 ℃, the engine coolant temperature is indeed high. Through the Mitchell database, got the car cooling fan control circuit diagram, the car fan control circuit for testing, the results are normal. Fan high and low speed normal operation, there is no fan control system circuit caused by the engine coolant temperature is too high fault. So fill the radiator coolant, connected to the PGM fault diagnostic apparatus, climbing road test. During the climbing process, the temperature of the coolant monitored by the PGM is within the normal range, and the fan's high and low speed operation signal is clear. After climbing the top of the hill, open the engine hatch, we found that the fast idle thermosensitive valve seat has a chronic water signs, is not the chronic water leakage caused by the engine coolant temperature is too high? The last maintenance, and did not find this seat There is a phenomenon of chronic seepage, because the fault is always random. Back to the factory, we replaced the fast idle heat valve and related small water pipes. Due to the demolition of the pipe, found in the coolant there are oil and water mixture, may be the last time to replace the cylinder pad, there is no clean up the oil. Fill the cleaning fluid to the radiator several times after cleaning, add antifreeze row of cooling system in the air. By road test, the engine coolant temperature is normal. So once again completed delivery.
   Never thought that the car and no more than half of the vehicle again repair, then the owner of the views of a very large, said spent so much money, did not repair the car, do not want to repair later, the corporate image has been great Influence, maintenance stalled. Why the maintenance of the two has not yet put the engine coolant temperature anomalies completely solve the problem? Where is the root of the fault? We have conducted in-depth discussion and research, the final decision to remove the left and right two cylinder head to carefully check The This time we found in the cylinder water jacket a lot of yellow oil and water mixture, but the oil within the oil pan is not even mixed with cooling water. It is strange that only oil in the oil can enter the cooling system, but the cooling system of water can not enter the oil, is there a one-way valve at work?
    Maintenance personnel after careful analysis that: the engine in the process of running, the oil pressure (200 ~ 300kPa) in the engine above the load above, always greater than the cooling system in the circulating water pressure (110kPa), resulting in the oil within the oil pressure into the cooling system , And then through the pump constantly rotating the water and oil into a yellow oil and water mixture. In order to verify that the above analysis is correct, we first check the two cylinder head carefully. Will the cylinder head be used for a long time, causing metal fatigue to produce cracks or trachoma? To check the cylinder head with cracks or trachoma, easier said than done! First, it is not cast iron cylinder head, magnetic detection can not be detected. Second, the detection of the powder, the operation is not easy. Finally, the maintenance staff thought of a soil approach, the two cylinder head of the oil hole with a stakes plug, and then the water into the cylinder head water jacket, so that the horizontal plane and cylinder head plane equal, then the compressed air pressure Into an oil channel that is not clogged, we choose the main oil passage of the cylinder to the oil hole on the cylinder head. Camshaft and valve rocker shaft of the lubricating oil hole in the relevant parts are not removed in the case, in a relatively sealed state, the operation did not appear leakage. When the application of compressed air 200kPa, the maintenance staff found in the oil and water jacket is the two cylinder combustion chamber at the junction of the waterway hole to take out the bubble.
    So the truth, because the engine cylinder head, especially the combustion chamber is quite poor working environment, coupled with the use of the engine for a long time, after the engine temperature, resulting in the junction of the two cylinder combustion chamber at the thinnest crack or trachoma, the root cause of failure to find The! After the replacement of two pure Honda cylinder head, the complex engine, once again on the engine cooling system in the oil and water mixture to clean up, after a long long distance test, and then found no yellow oil and water mixture, the engine water temperature is normal. This is due to the use of vehicles for a long time, parts damage more comprehensive fault finally removed.