Failure phenomenon: a 2009 annual Audi TT 2.0 L sedan, mileage 1 032 km, equipped with 2.0T FSI engine, DSG dual clutch transmission. Engine coolant reflect user level alarm lights lit on the vehicle instrument.
Check Analysis: pick the maintenance staff, on the basic vehicle inspection, we found coolant level in the reservoir ldquo; Minrdquo; tick or less, then that engine coolant level warning lamp lit Since the cooling system is due to a lack of coolant. After cooling liquid maintenance personnel to make up the test, warning lamp goes out, followed by a cooling system carefully examined and found no leakage, then delivery of the vehicle to the user.
15 days after the car because of the same phenomenon back to the factory overhaul. I took the car, first check the coolant level position, or below the coolant level found reservoir ldquo; Minrdquo; scale, indicating the presence of abnormality in the consumption of coolant cooling system. Causes abnormality in the consumption of cooling liquid a cooling system including an engine and an external leak ldquo; boil rdquo; due to internal friction. I first using a dedicated public VAS5052 engine system fault diagnostic testing, fault code is not found, the data stream is also no exception. Then, using a cooling system pressure tester for testing the static pressure of the cooling system, after 2 ~ 3 h constant liquid level in the coolant reservoir, together with the entire cooling system has not found leaking traces can exclude the cooling there is an external leakage, then the engine was suspected ldquo; boil rdquo; phenomenon.
spirit from simple to complex, outside to the inside of the maintenance concept, I first check the engine oil, found no oil or oily liquid level rises emulsification. Remove the spark plug 4 careful observation, we found signs four-cylinder spark plug center electrode in white, then four-cylinder audits. I connected to coolant pressure tester, the cooling system will be pressurized to 150 kPa, after half an hour, the cylinder 4 from the plug hole patient observation and bright flashlight, found every few minutes, you can see faintly 1 small drop of water droplets penetrate the top of the piston. In order to more clearly see the leakage site, the author uses an electronic endoscope, an observation which projects into the cylinder plug hole, when water leakage on the cylinder glance. Check this point, has been determinedPhenomenon exists consumed coolant inside a given engine. Well, the failure is specific cylinder head, cylinder block or cylinder head gasket problems caused it? To this end, the user’s consent, the author further engine has been overhauled.
FIG 1
After removing the cylinder head, the author of the cylinder head, the cylinder and the contact plane flatness waterways have been carefully examined, no found the problem, but there are signs of white top plan fourth cylinder of the piston engine (1), again proved that the problem of the fourth cylinder. Check the fourth key cylinder near the cylinder head gasket, cylinder head gasket author found that the presence of a little inner edge near the edge of the mouth of the fourth cylinder irregularities traces (FIG. 2), slowly open the second layer (of the cylinder head gasket 3 layer), and finally found near the edge of the mouth of a small interposed metal particles, after mounting the cylinder head, the cylinder head gasket affect flatness. While this does not affect the airtightness of the cylinder head gasket, but due to the metal particles is close to the edge of the cylinder crossing the water, at high temperature and pressure, it led to the cooling fluid into the cylinder. Since trace amounts infiltration, and not mixed with the oil passage, the coolant then enters the combustion chamber and completely evaporated into steam with the combustion exhaust gas is discharged together, so check oil level did not see the problem, an exhaust pipe from the trace water vapor can not see strange. However, the accumulated liquid coolant seepage losses eventually, leading to meter the coolant level alarm warning lights.
FIG. 2
troubleshooting: After replacing the cylinder head gasket, troubleshooting. By returning to the user that the cooling liquid consumption abnormal phenomenon never occurs, coolant level meter warning lights steady not appear again.
reviewed: coolant leaks usually is better to check the fault, but the fault of the car but it is a fight, dismantling the cylinder head only to find the problem. Just because the entire cylinder head gasket failure in the folder tiny metal particles caused by hard, plus the car with mileage of just over 1 000 km, and therefore contrary to some people’s surprise. Because it is small amount of leakage in the cylinder, to troubleshooting to bring a certain degree of difficulty, leakage is very weak, vehicles need some time to see a loss of coolant, maintenance personnel can easily mistake cooling system piping or fittings leak . New car factory quality problems, although relatively rare, but still inevitable, so maintenance personnel can not let any possible maintenance workThe cause of the failure, to avoid ldquo; granted rdquo; way of thinking and affect efficiency.
(Lu Jianping)