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Thread: HowTo -> Engine Cooling system: Replacing coolant vent hose on V12

  1. #1
    Join Date
    Oct 2007
    Mexico City, Mexico
    My Cars
    1999/750i - 2014/X5 x35i

    HowTo -> Engine Cooling system: Replacing coolant vent hose on V12

    Time needed: 2-4 hours depending on your skills

    Parts: vent hose (part no. 11531440104) + two new hose clamps (10-14mm) + extra HEX5mm, 6mm screw (not more than 12-14mm long) in case you drop it down between the two engine banks!

    Tools for removing the vent hose:
    ¼” socket set with long extension(s),
    ¼” universal joint,
    1/4” socket drive HEX 5mm,
    long thin screwdriver

    Other tools:
    Normal wrench set and torx driver bits

    I recently got leaking coolant being spray around right under the oil-filling cap. Realized it was the vent hose going from top of radiator to top of engine block. This vent hose consists of two smaller rubber hoses and one small steel pipe connected by a plastic ”Y” joint in the middle. This small steel pipe of the vent hose are being hold in place at the top of engine block between the (big) cooling steel pipes by a HEX 5mm, 6mm screw, which is very hard to reach. BMW TIS recommends removing engine wiring harness, fuel injection system and intake manifolds in order to reach this tiny screw. But with a lot of patience and steady hands, it is possible to reach this screw without removing vital parts of the engine:
    - Start work with engine cool and switched off!
    - Drain the coolant
    - Remove cooling fan (nut comes off clock wise),
    - Remove black “covering plate” just below oil filling cap, pull straight out, be careful, the “old” plastic is “crispy”
    - Remove the two emission control valves (in front and below of oil-filling cap, each has two small torx screws and a hose clamp for the rubber hoses)
    - Disconnect electrical wiring to thermostat house, remove hose to house
    - Remove thermostat house (four 10mm, 6mm bolts)
    - Disconnect electrical wiring to double thermostat switch and remove switch (located on top of water pump house),
    - Disconnect rubber end of old vent hose above fan cover and second rubber end at pipe just above water pump (11-14mm hose clamps, screw type or “BMW” type)

    With the ¼” socket, long extensions, the universal joint and the ¼” socket drive HEX 5mm you can now reach the screw horizontally. It takes some patience to get it out, but it is nothing compare to the patience needed to get the new screw back in on the new vent pipe. Don’t loose the screw, I did, but had a new one at hand. When screw is out, you can just lift pipe right up and then out horizontally.

    To get the new pipe installed. First disconnect wiring from no. 1 injection valve. Bending the vacum line a little you can actually see the hole where the steel pipe of the vent hose connects to the engine block. Put the HEX5mm screw in the steel pipe and move it in where the old one was. Be careful not to loose the screw! When pipe and screw is above engine block hole you will be able to see the screw down below of the back of no. 1 injection valve (see picture). Then put the thin screwdriver vertically down and try to turn the HEX screw. When it grips, give it a few turns and then press on the pipe to get the small o-ring on the pipe end in its right place (not a lot of force needed). Then move the ¼” socket, long extensions, the universal joint and the ¼” socket drive HEX 5mm horizontally in on top of the screw and fasten it. Use two new hose clamps to fasten the rubber ends of the vent hose.
    Reconnect everything you dismantled (including the wiring to the no. 1 injection valve!).

    Extra: You might also consider replacing the coolant, belts, thermostats, and coolant hoses, clean the radiator for insects and even replace the water pump while you are there! I did that (except for the water pump and belts). Also the two rubber hoses that are connected to the two emission control valves might need to be replaced (the rubber doesn’t seems to like the emission to well).
    Attached Images Attached Images
    Last edited by henrikhahn; 02-27-2011 at 10:12 PM.

  2. #2
    Join Date
    Oct 2007
    Mexico City, Mexico
    My Cars
    1999/750i - 2014/X5 x35i
    some more pictures!
    Attached Images Attached Images

  3. #3
    Join Date
    Dec 2016
    Springfield, VA
    My Cars
    2003 540iA

    FU on “HowTo -> Engine Cooling system: Replacing coolant vent hose on V12”

    Tried to do this on the HowTo thread but the thread has been locked by the Moderator... after 11 years, why not? Maybe if this info is good enough it could get added there?

    So I too had the Y-pipe failure and needed to replace it. Great write-up in the following thread on how to do it without removing the intake and everything else. Many thanks to OP. My notes below.

    1. I only replaced the Y-pipe. Daily driver so needed it for tomorrow.
    2. I did not remove anything other than the fan clutch, thermostat electrical connection, and the electrical connection to the injector. This might have cost more time but overall successful.
    3. Total time for me
    Start: 1300
    End: 2200
    But that includes 60 mins figuring out what is actually meant in the thread (sorry, original pics kinda suck), 65 mins at kids TKD practice, 75 mins dinner and kids bedtimes, 30 mins continuously chasing dogs away from coolant, 30 mins walking said dogs, and 45 mins explaining to wife/neighbors/etc what I was doing. So total actual time was probably 4 hrs from first action to end action (system bleeding).
    4. My pictures to add:
    This is the hex-driven screw you are going for as visible from injector 1

    This is what it looks like from the top and between the heater pipes when you have the hex seated

    5. I used magicfingers (and didn’t need a replacement screw) but if you don’t at least have the magnetic tool don’t even think about this.
    6. OP wasn’t kidding when saying patience to take it out is trying; patience going in... I had to take at least five frustration breaks putting that damn screw in and almost said f-it, it probably doesn’t need the screw twice. If you are impatient, stop and do not proceed.

    Again, thanks to the OP for the thread!

    2001 750iL DD74441

    RIP: 2003 540iA Sport GS56111
    H&R front springs, Ultimate Cup Holder, Euro Dash & Armrest, Grom, BavSound Stage1

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