I have seen several posts where the hose coming from the front of the valve cover going to the oil separator was damaged during removal of the valve cover. Below is DIY on how to replace the hose out of a 2001 325i.
This replacement can be completed in 30 min to an hour.
Background: the plastic hose gets brittle with age. The older the car, i.e. more than 7 years old, the more likely it will be brittle. If your car is older than 7 years, I recommend replacing the oil separator and all associated hoses to the separator. Failure timeframe for cars in northern or colder climates are shorter than given. The extreme hot and cold cycle shortens the life expectancy of the plastic components. Should you decide to do the oil separator as well, check this out: http://www.bimmerfest.com/forums/showthread.php?t=323335
Warning: The older the oil separator, the more likely it could break doing this procedure. However, the plastic to the oil separator is thicker compared to the hose so it should be more durable. Do this project at your own risk. All information given are for reference only.
Dissassembly
Remove front air duct
Remove air filter box assembly
Set aside the power steering reservoir assembly
Disconnect 4 electrical connectors
Move fuel breather valve to increase access area
Optional. If you have large hands or need more room, remove the oil pressure switch. Use an adjustable wrench to take it out. Tip: Scribe a line across the nut to the frame using a marker. During installation, you have a reference mark on how much torque to use. Do clean the copper washer and mating surface before installation. It is best to replace the washer, if available. Dimension of washer: 16.1mm o.d., 11.7 mm i.d.
We now have more room to access the lower connector with the electrical wirings and fuel breather valve assembly out of the way. Pictue 2.
The upper and lower hose connectors are identical. Study, understand, and practice on the upper connector how it works.
Squeeze the ring by the ribbed section of the connector ring and pull connector out. These ribbed sections are on opposite sides of the ring. If you run into any difficulty, the rubber o-ring seal may have seized. Twist the connector slightly clockwise and counter-clockwise from its pivot point to dislodge any obstructions.
Connecting the new hose is simple. The 90-deg. elbow of the hose goes to the valve cover while other end connects to the oil separator. Push the connector in until you hear it snap. Pull lightly to be sure the connection is secure.
This replacement can be completed in 30 min to an hour.
Background: the plastic hose gets brittle with age. The older the car, i.e. more than 7 years old, the more likely it will be brittle. If your car is older than 7 years, I recommend replacing the oil separator and all associated hoses to the separator. Failure timeframe for cars in northern or colder climates are shorter than given. The extreme hot and cold cycle shortens the life expectancy of the plastic components. Should you decide to do the oil separator as well, check this out: http://www.bimmerfest.com/forums/showthread.php?t=323335
Warning: The older the oil separator, the more likely it could break doing this procedure. However, the plastic to the oil separator is thicker compared to the hose so it should be more durable. Do this project at your own risk. All information given are for reference only.
Dissassembly
Remove front air duct
- Remove 3 plastic expanding fasteners. Raise middle pin and pull out expanding fastener.
- Remove air duct
Remove air filter box assembly
- Remove 2 10mm bolt holding the air filter box assembly
- Disconnect the electrical harness to the MAF sensor
- Loosen hose clamp between MAF and upper air intake boot
Set aside the power steering reservoir assembly
- Remove the 2 bolts (13mm) holding the power steering assembly
- Move steering reservoir out of the work area
Disconnect 4 electrical connectors
- Oil pressure sensor
- Alternator (depending which alternator came with your car, this may not apply)
- Fuel breather valve
- Oil temperature sensor
Move fuel breather valve to increase access area
- Disconnect lower fuel breather valve hose from clip
- Remove fuel breather valve from mount bracket
Optional. If you have large hands or need more room, remove the oil pressure switch. Use an adjustable wrench to take it out. Tip: Scribe a line across the nut to the frame using a marker. During installation, you have a reference mark on how much torque to use. Do clean the copper washer and mating surface before installation. It is best to replace the washer, if available. Dimension of washer: 16.1mm o.d., 11.7 mm i.d.
We now have more room to access the lower connector with the electrical wirings and fuel breather valve assembly out of the way. Pictue 2.
The upper and lower hose connectors are identical. Study, understand, and practice on the upper connector how it works.
Squeeze the ring by the ribbed section of the connector ring and pull connector out. These ribbed sections are on opposite sides of the ring. If you run into any difficulty, the rubber o-ring seal may have seized. Twist the connector slightly clockwise and counter-clockwise from its pivot point to dislodge any obstructions.
Connecting the new hose is simple. The 90-deg. elbow of the hose goes to the valve cover while other end connects to the oil separator. Push the connector in until you hear it snap. Pull lightly to be sure the connection is secure.