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DIY: N54 Engine Supply Coolant Pipe
Removal & Replacement
Published by Augster
01-25-2014
Post DIY: N54 Engine Supply Coolant Pipe

I could not find any guides for replacing the Engine Supply Coolant Pump Pipe, aka Water Pipe, for the N54, nor was a procedure listed in the Bentley manual. TIS (2007) was very vague in describing the procedure, and the section directed to removal of the "primary catalytic converters" (i.e. downpipes) outlined steps to actually cut off the exhaust system. Hence my quest to document my trials and tribulations within this more detailed DIY undertaking.

If you're leaking coolant at the connection of the water pipe to the engine block (bad gasket), or to the water pump (bad hose), you need this DIY. The gasket is sold individually, however, the rubber hose going to the water pump is not. It is attached firmly to the pipe with a thick clamp and is curved, although the possibility does exist to locate a same-sized hose with a similar bend in which a suitable section can be cut off and a regular hose clamp used to attach it to your existing pipe. However, keep in mind that the hose sits barely 2 inches away from the side and slightly above the front turbo and thus will be exposed to high heat. I seriously doubt a standard radiator hose will be able to withstand that situation for very long.



Be forewarned, this is not for the faint of heart as it involves removal of the downpipes plus working in confined spaces. I would imagine the vast majority would rather elect to pay someone to do the replacement but it probably won't be cheap. But for me, I gained valuable experience in preparation for when I do actually replace my DP's with an aftermarket catless set.

As this involves draining the coolant, you could combine this procedure with other projects that involve coolant draining, such as water pump and thermostat replacement (which I already replaced two months earlier), or an OFHG R&R, which is what I did; I posted a DIY Addendum involving the Oil Filter Control Housing gasket.

Tools and Materials Used
  • 1 gallon BMW Antifreeze/Coolant, PN 82141467704
  • 2 Exhaust Gaskets, PN 18307553603
  • 1 Engine Supply-Coolant Pump Pipe, PN 11537558522 (if replacing entire water pipe)
    or
    1 Gasket, PN 11537545302 (if just replacing bad gasket)
  • 1 gallon Distilled Water
  • PB Blaster Penetrating Catalyst Lubricant (DP exhaust nuts)
  • Copper Anti-Seize Lubricant (high-temp applications)
  • Carburetor or Brake Cleaner (to clean engine block gasket surface)
  • Masking Tape (securing DP O2 sensors in pre-wound position)
  • Shop Towels/Rags
  • Nitrile Gloves
  • 6mm Socket (hose clamps)
  • 8mm Socket (splash guards)
  • 10mm Socket (expansion tank)
  • 12mm Socket (rear turbo DP bracket and exhaust nuts)
  • 13mm Socket (DP V-band clamps; sway bar clamp nuts)
  • E8 External Torx Socket (water pipe bolts)
  • E10 External Torx Socket (exhaust bracket clamp bolt)
  • E12 External Torx Socket (steering rack bolts)
  • T25 Torx Bit (tie rod boot heat shield)
  • T30 Torx Socket (turbo coolant supply clamp bolts)
  • 12mm Ratcheting Wrench (front turbo DP bracket nut)
  • 16mm Open-End Wrench (fixing steering rack nuts)
  • 22mm Open-End Wrench (breaking loose/tightening O2 sensors)
  • 6" Adjustable Wrench (quick O2 sensor removal/replacement)
  • 1/4" Hex Shank to 1/4" Square Drive Adapter (tie rod boot heat shield)
  • 3/8" Universal Joint (rear turbo DP bracket nut)
  • 3" Long 1/4" Square Drive Extension (water pipe bolts)
  • 6" Long 1/4" Square Drive Flexible Extension (hose clamps)
  • 6" Long 3/8" Square Drive Extension
  • 10" Long 3/8" Square Drive Extension
  • 1/4" Square Drive Ratchet
  • 3/8" Square Drive Ratchet
  • 3/8" Air Ratchet (makes for easy work on V-band clamp bolts and exhaust fasteners)
  • Torque Wrench
  • Flat-Blade Screwdrivers
  • Hose Removal Tool or Hook Pick Tool (breaking hard-to-reach coolant hose bonds)
  • Long Pinch/Pry Bar (unseating V-band clamps)
  • Hammer (tapping pinch/pry bar)
  • Coolant Drain Pan
  • Headlight (to easily illuminate areas while working)
  • Flashlight
  • Leather Gloves (to safely clean block mounting pad)
  • Floor Jack (to assist raising exhaust)
  • Ramps or Jack Stands
  • Wheel Chocks



Positioning the new water pipe to help visualize its orientation, locate key connection points, and plan a strategy for its removal.




Engine Supply Coolant Pump Pipe Removal and Replacement Procedures

Step 1: Raise vehicle, chock wheels if necessary, and remove front splash guard and splash guard brackets with 8mm socket. I only raised the front of the car as this allows sufficient room to maneuver the DP's in and out and access the exhaust clamp, but raising the back as well may help in reconnecting the exhaust to the downpipes if you do not have anyone assisting you.

Step 2: Remove the down-pipes. Since there are numerous DP DIY guides available, I will refer you to a video one I utilized most: How To Install AR Design Downpipes, with the following suggestions:
  • It's easier to simply unplug the connectors for the rear O2 sensors and keep the sensors mounted and untouched. They don't get in the way when removing and reinstalling the DP's.
  • I used a 12mm ratcheting wrench to remove the front (inboard) DP mounting stud nut; easier than trying to fit a regular socket and universal joint into the tight space.
  • There is no need to pry the DP's off the mounting bracket as once the V-band clamps are removed they come off the bracket easily.
  • I removed the tie rod boot heat shield completely instead of bending it out of the way like most do. Using a T25 torx bit on a 1/4" square drive adapter and 1/4" ratchet, I was able to get my hand up to the upper outer screw. Reinstalling the screws took patience and dexterity but I was able to get them back on without much fuss. I also unbolted the sway bar which gave me a little more room to maneuver the steering rack out of the way for more access.
  • An air ratchet makes quick work on the V-band clamp bolts. Very handy tool to have!
  • After breaking loose the front O2 sensors with a 22mm wrench, I used a short adjustable wrench (6") to assist in their removal/replacement instead of resorting to cutting up a 22mm wrench like they did in the video.
  • Once each front O2 sensor was removed, I maintained their "pre-wound" position by taping them to the nearby intake charge pipe. This way, you don't have to pre-wind them prior to re-installation, which can be hit or miss if you didn't count the number of turns they made when removing them.



Step 3: Drain cooling system and remove thermostat-to-water pump hose to gain access to the water pipe hose. Remove the expansion tank cap, unplug water pump electrical connector, loosen the 6mm hose clamp on the U-shaped hose to the water pump and work the hose off slowly with a screwdriver to allow controlled coolant drainage into a catch pan. Once there is no more coolant draining out, loosen the hose clamp on the other end to the thermostat and work the hose completely off, draining any remaining coolant. Optionally, you can first remove the intercooler and drain most of the coolant through the radiator drain plug to lessen the amount of messy spillage and quicken the draining than just through the water pump alone; reinstall the drain plug when coolant stops draining.



Step 4: Remove the coolant supply hold-down clamp T30 bolts and the lower heat shield E8 bolts; freeing the lower part of the heat shields will allow you to move the supply lines out of the way later. If you can wrest the supply lines out of the water pipe, then do so now. Mine were almost impossible to budge so I continued disassembly. The photo below shows the clamp bolts already removed:



Step 5: Remove the 4 water pipe E8 flange bolts and separate the pipe from the block. This should allow more flexibility in removing the supply lines.

Step 6: Wrangle the supply line fittings enough to gain clearance to insert a flat-blade screwdriver between the fittings and the water pipe mount, then alternating back and forth from the hold-down clamp to the fitting pry the supply lines free from the water pipe: do NOT mistakenly pry the groove in the fitting meant for the hold-down clamp. Have rags available to catch any spilling coolant. I've already installed the new water pipe when I took these photos for reference:




Step 7: Loosen the hose clamp on the hose connected to the water pump, then break the bond between the hose and water pump outlet using a screwdriver or hose removal tool.

Step 8: Loosen the hose clamp on the coolant bypass hose connected to the branch tube and break the sealing bond. Due to it's location, it's too difficult to jab in screwdriver all around its circumference so a hose removal tool or a hook pick tool would be ideal. My hose clamp was clocked in such a way that made it impossible to get to without removing the expansion tank:



Even with the expansion tank removed, I couldn't get a socket nor screwdriver onto it because it was pointed directly towards the frame rail. I was forced into painstakingly small turns with an adjustable wrench.



Step 9: Maneuver the water pipe to clear the heat shields, allowing you room to pull its hose off the water pump and the branch tube from the bypass hose. Guide the water pipe out from behind the crossmember.

Step 10: Clean the block mounting pad surface of all residual gasket material with carb/brake cleaner while wearing leather gloves. The machined edges may have sharp residual aluminum shards; mine did and it sheared off a 3/8" long by 1/8" deep chunk of skin off my index finger; very painfully I might add.



Here are comparison photos between the new water pipe and the old:



The old hose end was badly deformed:



But the source of the leak was a crack on the inner side of the hose, not visible when installed in the dark, cramped confines of the engine compartment:



Step 11: Transfer the hose clamps to the new water pipe and ensure they are clocked correctly that they can be accessed for tightening while on the engine. I orientated the bypass hose clamp such that it would be accessible from below:



Step 12: Install water pipe from behind crossmember, fit bypass hose onto branch tube, water pipe hose to water pump, then finally seat water pipe flange between the heat shields and onto block mounting pad.

Step 13: Install water pipe bolts and torque to 9 Nm. Install turbo coolant supply pipes and clamp bolts, tightening them to 20 Nm.

Step 14: Fully seat the bypass hose lining up its groove with the alignment pin on the bypass tube, position the hose clamp between the white parallel lines on the hose and tighten with a 6mm socket to 3 Nm (my hands are specially calibrated for 3 Nm so I didn't need a torque wrench ).



Step 15: Fully seat the water pipe hose to water pump, position the hose clamp within the guide lines and tighten to 3 Nm.

Step 16: Reinstall the thermostat-to-water pump hose, again lining up the hose clamps between the guidelines and tighten to 3 Nm. Reattach water pump electrical connector.

Step 17: Reinstall the expansion tank (if removed), fill cooling system with 50/50 mix of BMW Antifreeze and Distilled Water, perform coolant bleeding procedures, and check for leaks.

Step 18: If the cooling system checks out, reinstall intercooler if removed, then reinstall DP's, with the following suggestions:
  • Don't forget to install the Turbo-to-Downpipe-Gaskets into the turbo flanges first after loosely hanging the V-band clamps but before installing the downpipes. The video doesn't mention these at any point; one of mine remained seated after removing the DPs but the other dropped out. Just be careful when guiding the DP's into place by not bumping the turbos and the gaskets should remain in place.

  • The OEM downpipe mounting tabs have U-shaped slots that line up with pins on the mounting bracket to ensure they are properly indexed (rotated correctly to line up the exhaust studs to the exhaust pipes). Once you get the DP up onto the turbos and loosely fitted the V-band clamps and bolts, rotate the DP's until they easily guide into the bracket; should not require excessive force to slip into bracket if properly aligned. By the way, my bracket (for an automatic, PN 18207553610) had both U-slots for the DP mounting studs but the rendered image on RealOEM and the only stock photo provided by ECS Tuning (manual, PN 18207553609) has only one U-slot while the other for the front (inboard) DP is closed. If your mounting bracket is like the one below, you may need to lever the bracket to slip over the DP mounting stud.

  • I applied anti-seize to the exhaust studs, exhaust clamp stud, and V-band clamp bolts, although it's probably not necessary on the latter as they showed no signs of rusting and were very easy to remove.
  • Use a floor jack to raise the exhaust to line up with the DPs, and if necessary, have someone push on the right exhaust tip to close the gap between the exhaust and DPs. Only after I ensured the exhaust studs properly lined up with the exhaust flange did I finally tighten the V-band bolts and DP mounting stud nuts. I then installed and tightened the exhaust stud nuts to 21 NM and exhaust clamp to 19 Nm.
  • Unless your exhaust gaskets are relatively new, you should install new ones if they were like mine where the metallic coating began flaking off after removal and the round inner gasket separated from the oval outer gasket.

Step 19: Reinstall tie rod boot heat shield with T25 torx bit. Patience is required when carefully rethreading the self-tapping screws.

Step 20: Pre-stage steering rack nuts on top of subframe, using the bolts to line them up with the holes. Mount the steering rack into subframe aligned to the holes, slowly insert bolts, shifting steering rack as necessary, and carefully thread bolts into nuts. Once both are properly threaded, fix the nuts with 16mm open-end wrench and torque the E12 studs to 50 Nm. If sway bar was unbolted, mount and torque the 13mm nuts to 21 Nm: if vehicle was raised onto jack stands with front suspension hanging, loosely attach nuts, wait until vehicle is back down and suspension has settled (short test drive) before torquing sway bar nuts.

Once everything has been verified assembled with no "extra" parts remaining, start the car and check for any exhaust and coolant leaks. If all is good-to-go, install the splash guards and drive away with peace of mind and a big pat on the back for tackling a difficult project yourself!
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