The crankcase ventilation system is an integral part of the operation of the internal combustion engine in cars. Nissan, ensuring the removal of exhaust gases from the crankcase of the intake system. In modern engines such as MR20DE or VQ35DE, this process is regulated by a special valve that prevents an increase in pressure and the release of harmful substances into the atmosphere.
Ignoring problems with this part can lead to serious consequences, including ruptured seals, oil getting into the intercooler, and even water hammer. Understanding the operating principle and timely diagnostics will help you avoid costly engine repairs.
Owners Nissan Qashqai, X-Trail and other models are often faced with the fact that the crankcase ventilation valve (CVG) fails due to natural wear or contamination. It is important to distinguish the symptoms of this failure from other problems with the air supply system so as not to replace unnecessary components.
How the crankcase ventilation system works on Nissan
During engine operation, part of the fuel-air mixture and combustion products enters the crankcase through the gaps of the piston rings. Without the removal of these gases, the pressure inside the crankcase increases, which leads to oil being squeezed out through the seals and gaskets.
The crankcase ventilation valve, often called the "breather", operates depending on the operating mode of the engine. At idle speed it blocks or restricts the flow, and when loaded it opens, allowing gases to flow into the intake manifold for subsequent afterburning.
In motors Nissan with the system turbocharging The device becomes more complicated: it uses an oil separator, which separates the oil mist from the gases before they enter the intake system. The efficiency of this unit is critical to the cleanliness of the intake tract.
If the mechanism jams in the open position, the engine begins to consume excess oil, and if it is closed, the pressure increases, leading to leaks. Regularly checking the condition of the ventilation system should be part of routine maintenance.
The main symptoms of a malfunction of the KVKG valve
The first symptoms of a problem are often extraneous sounds. If you hear a whistling or hissing sound when the engine is running, this may indicate that the valve diaphragm has ruptured or is stuck, creating a leak in the system.
Another clear sign is increased oil consumption without visible external leaks. Oil begins to enter the intake manifold, burning along with the fuel, which leads to the formation of carbon deposits on the spark plugs and catalyst.
- 🔥 Increased fuel consumption and unstable engine operation at idle.
- 💨 The appearance of blue smoke from the exhaust pipe, especially during acceleration.
- 🔧 The Check Engine light comes on with error codes related to the crankcase ventilation system.
By car Nissan Note and Tienda The throttle valve is often clogged with oil deposits, which is an indirect sign of a malfunction of the CVCG. In this case, not only valve replacement is required, but also cleaning of the intake tract.
⚠️ Attention: If you notice oil in the intercooler pipes of a turbocharged engine, do not delay diagnostics. This is a direct signal that the separator or crankcase ventilation valve has failed.
Diagnostics and methods for checking the node
For an accurate diagnosis, it is necessary to visually inspect the pipes and the valve itself. Remove the pipe leading to the valve and check for large amounts of oil condensate or carbon deposits. A clean hose while the engine is running is a good sign.
Check the valve diaphragm. On many models Nissan the valve is built into the valve cover cover. Disconnect the hose and try to blow into the hole. The resistance should be noticeable, and when air passes, a click or sound change should be heard.
Use a pressure gauge to measure crankcase pressure. Connect the device through the probe hole or spark plug hole. The pressure should not exceed the permissible values (usually about 0.05-0.1 bar) when the engine is running at different speeds.
- Increased oil consumption
- Engine whistling
- Smoke from the exhaust pipe
- Check Engine Light
Specifics of valve design on different models
The design of the ventilation system varies depending on the generation and type of engine. On naturally aspirated engines of the series MR the valve is often constructed as a single unit with the valve cover, making replacement difficult without removing the entire cover.
In turbocharged versions such as 2.0 DIG-T, the system includes a separate oil separator, which can be integrated into the valve cover or configured as a separate unit. This increases the efficiency of gas purification, but increases the cost of repairs.
On older models, for example, Nissan Primera or Sentra, simpler valves were used that could be replaced separately. However, they are also subject to membrane wear and channel contamination.
It is important to note that on some models Nissan With a continuously variable transmission (CVT), improper operation of the crankcase ventilation can indirectly affect transmission cooling through the recirculation system, although this is rare.
Why don't some Nissans have a separate valve?
On a number of modern engines, the crankcase ventilation valve is a non-separable part of the valve cover. If the membrane breaks, you have to replace the entire cover assembly, which significantly increases the cost of repairs, but guarantees the tightness of the connection.
Instructions for replacing the ventilation valve
Replacing a valve requires care and consistency. Allow the engine to cool before starting work to avoid burns and deformation of plastic parts.
You will need to remove the air filter and the pipes connecting the valve to the intake manifold. Disconnect the electrical connectors if the valve is solenoid controlled (on some modern versions).
☑️ Preparation for valve replacement
If the valve is built into the cover, you will need to unscrew the cover bolts, first clearing the area of dirt. Be careful not to damage the cover gasket if you plan to reuse it (although it is better to replace it with a new one).
Install the new valve or cover assembly, observing the tightening torque of the bolts. Improper tightening may result in oil leakage and further failure. Connect the pipes and connectors, then start the engine and check for leaks.
⚠️ Attention: When replacing the valve cover on engines QR25DE Be sure to use sealant where it mates with the cylinder block, as the factory gasket may not provide a perfect seal when reinstalled.
Repair cost comparison chart
The cost of repair varies greatly depending on the vehicle model and valve type. Original spare parts are always more expensive than analogues, but ensure durability and compliance with factory specifications.
| Model Nissan | Engine type | Original part (RUB) | Analog (RUB) | Work (rub.) |
|---|---|---|---|---|
| Qashqai (J10, J11) | MR20DE | 15 000 - 25 000 | 8 000 - 12 000 | 3 000 - 5 000 |
| X-Trail (T31, T32) | MR20DE / QR25DE | 18 000 - 28 000 | 9 000 - 14 000 | 4 000 - 6 000 |
| Teana (J32, J33) | VQ25DE / VQ35DE | 20 000 - 35 000 | 12 000 - 18 000 | 5 000 - 8 000 |
| Note / Tiida | HQ15DE / HR16DE | 10 000 - 18 000 | 5 000 - 8 000 | 2 000 - 4 000 |
Before ordering a spare part, be sure to check the vehicle's VIN code. On the same model in different years of production, valves with different fastenings and flow characteristics can be installed.
Many car owners try to clean the old valve, but this rarely has a long-term effect. The membrane loses elasticity over time, and chemical reagents cannot restore its physical properties.
If you decide to replace the valve yourself, make sure you have access to all fasteners. In some engine compartments Nissan Space is limited and you will need extensions and gimbals to remove the bolts.
Prevention and service life extension
The quality of engine oil directly affects the life of the crankcase ventilation valve. Use only certified oils recommended by the manufacturer and change them strictly according to the regulations.
Overheating the engine also accelerates wear of the rubber valve elements. Monitor the condition of the cooling system and replace antifreeze on time to avoid engine overheating.
Regularly checking the condition of the ventilation system pipes and hoses will help identify problems at an early stage. Cracks or breaks in the hoses can mimic a broken valve, so they also need to be replaced if necessary.
Timely oil changes and the use of high-quality consumables are the most effective way to extend the life of the crankcase ventilation valve and avoid problems with crankcase pressure.
If the vehicle is driven on frequent short journeys or in dusty environments, service intervals should be reduced. Under such conditions, the system becomes contaminated faster.
This increases the cost, but eliminates the risk of repeated breakdown due to poor installation.
Frequently asked questions from Nissan owners
Is it possible to drive with a faulty crankcase ventilation valve?
Short term - yes, but it is dangerous. Long-term operation will lead to increased pressure in the crankcase, squeezing out the seals, contamination of the intake tract and possible failure of the turbine or catalyst. It is recommended to correct the problem as soon as possible.
Why does the engine stall after replacing the valve?
Most often this is due to leaky connections or improper installation. Check all pipes for cracks and make sure the valve cover gasket is installed correctly. It is also possible that the intake manifold was very dirty, and after replacing the valve, the engine's operating mode changed.
How often do you need to change the KVKV valve on a Nissan?
There is no official replacement regulation. The node is considered a resource node and changes as it fails. This usually occurs between 100,000 and 150,000 km, but depends on driving style and fuel quality.
Is it possible to replace just the valve diaphragm?
On most modern models Nissan this is not possible since the diaphragm is integrated into the valve cover. In rare cases, replacement is possible on older models, but the reliability of such repairs is lower than replacing the complete unit.
Does a faulty KVKG affect fuel consumption?
Yes, a faulty valve disrupts the composition of the fuel-air mixture. If it is stuck in the closed position, pressure in the crankcase increases and can affect the operation of the sensors. If it is open, the engine sucks in excess oil, which changes combustion parameters and increases consumption.