[acediac]

Hi All,

I just replaced the Oil Filter housing, water pump and cylinder head coolant line on my B48 and thought I would share my experience in case it helps anyone.

My car: 2016 F30 330i LCI with B48 engine, 100k km (60k miles)

The catalyst for this was a failure of the cylinder head - expansion tank coolant line which left me driving without coolant for about 15 minutes as I tried to reach home asap. Although I had plenty of warning lights including the red "stop now!" come on a few times, the engine seems to have survived any major damage (although next time I would probably just pull over and call the tow truck). The temperature gauge on the instrument cluster seems to be just the oil temp not the coolant, and it did not seem to rise appreciably the whole time (was around 110C or 3/8 of the way from the left which is normal). After this ordeal I read up all the threads on what else can fail as I did not want this to happen again.

I ended up replacing:

• Cylinder head - expansion tank coolant connector pipe (aka 17129845173, 17128740118, 17125A05950) It has had many revisions and there may be a newer revision now as realoem shows "not found" for any of these numbers 17125A05950*
  (If you are just doing this pipe, it is possible to just remove the front bracket holding the throttle body and snake the pipe under the intake muffler, 30 minute job depending how quickly you can unhook and reconnect the engine side connector.)
• Oil Filter Housing 11428596283
• Oil Filter Housing to engine block gasket (this should be included with the housing above if you buy a new one) 11428591460
• Coolant water pump with component carrier 11517644809
  (To save money, you can just replace the coolant water pump (11518638026) and redo the seals on the component carrier)
• Gasket for heat exchanger - oil filter housing 11428591462
• Connector branch from engine block to coolant pipe (recommended to change this plastic part) 11118511205
• 3x 1.5L Coolant (This car came with blue but I used the newer green version)

While I was in there, I also replaced:

• Seal to intake ports for intake system (need 4) 11618637800
• Throttle body Gasket (need 2) 13547563377
• O-ring for heat management module 11538658573
• Gasket for heat management module 11538658574
• Intake muffler to turbo seal 13717601067
• turbo to Charge air pipe seal 13718642240
• alternator Belt drive 11288646475

After some deliberation, I decided to use aftermarket parts for the following:
Aluminium oil filter housing
There are many available but they all use the same pictures, which leads me to believe there is just one factory making these in China. I bought from here but just search for the part number in Amazon: (https://www.amazon.com.au/dp/B0BZS2LZMQ)
This was 75% the price of a new genuine plastic one, and includes the heat diffuser module and gaskets and screws!
[Edit: for some reason, the link is now going to a plastic version of the part from the seller. You can find other sellers of the aluminium version by searching for 11428596283 on Amazon]


Aluminium connector branch
(https://www.amazon.com.au/1111851120.../dp/B0CH3L52JC) - These do not come with a gasket and the mounting surface does not contain a groove for a gasket. I used a bead of the same silicone that was recommended for the water pump (Loctite 5970 gasket sealant 83190404517).

Obviously it is not time tested but I was quite pleased overall with the quality of the aluminium parts. Dimensions seem to be spot on. Just to be safe, I de-burred the inside of the connecting branch and some parts of the oil filter housing (some minor small chads in the inside junctions of some of the holes) with a Dremel and hand file, and washed the parts and dried them in an oven. I intend to do another oil change after 3k kms in case there are any metal particles circulating.

Silicone connector coolant pipe (https://www.amazon.com.au/1712874011.../dp/B0C6J3V43R)
I was very impressed with the silicone connector pipe replacement. I believe that the failures with the OEM pipes are due to constant movement between the engine and the bolted down expansion tank acting on the rigid pipe with plastic connectors. Not only is the silicone aftermarket more flexible, it comes with brass connectors! I'm confident this won't fail any time soon.

Here are the basic steps that I followed. You should refer to nwts for full instructions, I will not provide links for legal reasons.

• Disconnect battery earth (Tie a rope to the trunk latch hook to prevent it from closing)
• Remove engine bay underbody cover
• Drain low temperature coolant circuit (connector near radiator on the right side of car / left if you are facing the car)
• Drain the high temperature coolant circuit (connector on front left side of car / right if you are facing the car)
• Remove rear weatherstrip + upper strut brace + rear engine acoustic foam
• Loosen oil filter and drain engine oil
• Remove electronics box / DME (not strictly necessary but will make things a lot easier, take lots of photos before removal)
• Remove intake filter housing + clean air pipe to throttle body
• remove valve + hoses on top of air intake plenum and unbolt the plenum. Work the plenum loose, flip over the plenum to disconnect two pipes underneath.
• Remove connecting branch
• unbolt heat exchanger for automatic transmission
• remove oil filter housing
• Preload the belt tensioner with a wrench and secure with a pin (Be careful of this step, the manual warns this could be dangerous. There is a special pin 83300496268 used for locking the tensioner in place but I used a drill bit. However I was extremely aware that it could snap at any moment and fly off and pierce my eye. I returned the tensioner to the default position as soon as I unbolted the alternator. To be safe, it is best to purchase the special rod for this purpose.)
• unhook the belt and remove the bolts for the alternator and remove the alternator.
• unbolt and remove a/c compressor (see notes)
• Remove component carrier
• Remove heat management module (if doing the seals)

When reassembling, take note of tightening torque and sequence from the manual.

Procedure for bleeding coolant circuits (after vacuum filling):
Note you are meant to fill the coolant with the heater turned to maximum (I presume it opens extra passageways for the coolant). I'm not sure it is a good idea to turn the ignition on to set the heater when the coolant circuit is dry, so best to set the heater before disconnecting the battery at the very start of the job.

Low temp circuit:

• Connect battery charger
• Fill low temp reservoir to max and close cap
• Turn on ignition
• Switch on low beam (all the way clock wise) and turn on hazard lights
• Check driving experience is not ECO-Pro
• Set heating to maximum and blower to minimum (1 bar)
• Press accelerator pedal for 10 seconds (don't start engine). You will hear the pump start up.
• Leave pumps running (engine off) for 15 minutes.
• Turn off and fill low temp reservoir to max.

High temp circuit:

1. Fill high temp reservoir to max and close cap
2. Turn on ignition
3. Switch on low beam (all the way clock wise) and turn on hazard lights
4. Check driving experience is not ECO-Pro
5. Set heating to maximum and blower to minimum (1 bar)
6. Press accelerator pedal for 10 seconds (don't start engine). You will hear the pump start up.
7. Start engine. It will have increased 1200rpm idle if the procedure is started correctly.
8. Wait 1 minute then:
9. Rev engine to 3000rpm and hold for 10 seconds. Release and idle for 10 seconds
10. Repeat the above for 5 cycles.
11. Leave the car for 11 minutes to finish the bleed procedure
12. Fill high temp reservoir to max once engine is cool

Notes
As with any major disassembly, take lots of photos at every stage. Label connectors. I like to sticky tape screws in the same slots as the piece it comes off in so I don't forget, or re-screw it in the hole after the piece comes off.

For the aftermarket pieces, I used 10Nm for all bolts with aluminium - aluminium surfaces and 8Nm for plastic to aluminium.

I bought the (genuine) component carrier with the water pump ($$$) but the carrier is a solid aluminium piece that should be fine to reuse. The only problem is, there are no gaskets for sale, the manual says to use Loctite 5970 83190404517. The new part comes from the factory with the silicone already applied at the carrier (I could actually tell it was formed from a bead of silicone, don't know why they don't just make a gasket) and the water pump already assembled (and presumably sealed, I didn't take it apart) against the carrier.
You can just replace the water pump without removing the carrier and it will save having to remove the alternator and a/c compressor, but the seal behind the carrier is also known to fail at some time.

Take care with the squeeze pipe fittings for the fuel breather lines. If you snap a connector, each of those plastic rigid pipes can cost as much USD$50+ to replace. Ask me how I know.
Most electrical connectors have a tab that must click out before it can be depressed. Most coolant hose connectors have a circlip wire that must be pulled out to the notch before unplugging. Be careful as the circlips can come completely off and fly away under tension.

It is possible to get the 4th bottom bolt of the oil filter housing from above. However, I found it easier to undo the heat exchanger for automatic transmission to shift it aside for access (no need to unplug the fluid hoses). One of those fixing bolts is just below the bottom bolt of the oil filter housing, the other two are a tight reach from underneath the car. 1/4" drive E10 and E8 torx sockets with swivel joints and extenders will really help. The smaller the better.

With the intake plenum off, this might be a good time to clean those intake valve stems too.

Despite what the manual says, it is not necessary to drain the a/c gas to remove the a/c compressor from the water pump component carrier, just set the compressor slightly aside after unbolting from the carrier. The compressor was a tight fit on the component carrier and I needed to carefully pry it loose after unbolting.

I used a vacuum kit (pictured below) to pump out the air from the low temp circuit and high temp circuit. You need to make sure there are two different sealing caps that fit the two reservoir openings. I made sure each circuit held vacuum for at least 5 minutes before filling (about -50 cmHg with my pump). I needed about three 1.5L bottles of coolant concentrate (diluted 50% with demineralised water) total to refill both circuits. Keep checking and topping up the coolant over the next few days of driving until it stops dropping.

When refilling the oil I poured some oil into the oil filter housing to help the initial flow. Needed about 5.5L total.

It is a good idea to take lots of photos and / or label the DME / electronics box connectors. Take note that some locations on the electronics box are unconnected.

I got plenty of warning lights and a DME failure when I started the car up after the job, but it turned out the DME plugs weren't plugged in properly. When reassembling, you need to start from the connector at the back of the engine bay and work towards the front, because the latch needs to start off almost horizontal before you push the whole plug down, otherwise it won't plug in all the way. Just because the latch locks back into vertical position is NOT a guarantee that it is properly seated. I had to reset all faults with ISTA+ after fixing the connection.

The upper strut brace uses aluminium bolts which are supposed to be tightened to 48Nm and stretched a further 90 degrees. Might want to replace 4x 07147270121 if you take it apart a few times.

All in all I took my sweet time over a few days, but it was not too difficult if you are moderately experienced at diy. Hope this helps!

[alexonahurry]

That's a pretty comprehensive manual, really helpful. I like the aluminum OFH - I got an updated one from BMW that's is still made from plastic but I got mine done about 15K miles ago.

[xyz8xyz]

Thanks for sharing, very useful information

[bryanlopez]

I believe my oil filter housing failed on me last night. Thanks for the thorough write up!
Do you mind correcting the link for the aluminum housing that you used? You used the link for the coolant pipe.

[acediac]

Originally Posted by bryanlopez

I believe my oil filter housing failed on me last night. Thanks for the thorough write up!
Do you mind correcting the link for the aluminum housing that you used? You used the link for the coolant pipe.

Sorry my bad, the link has been corrected in the post (but the seller doesn't seem to have it in stock any more, just search for 11428596283 for alternative sellers).

[angelforce]

I wish I was your neighborhood to watch you doing this show!

I clicked on all the links but it seems the suppliers got out of stock fast. All of them are unavailable for me.

I will plan to do this upgrades soon.

Would be great if BMW had done that by design. (But it would mean less service for their workshops later after warranty hehe)

Thank you so much for this comprehensive manual.

I wish you had filmed that to sell as a course haha since I am not super savvy on this kind of work…

[Moupe]

How is that silicone coolant pipe working out for you? Any signs of bulging or leaking?

Still unsure whether or not I buy the replacement BMW part or go with something aftermarket like what you purchased. I wish it was available in black instead of orange.

[cfm56d7b]

Super useful. Ought to be pinned. Thank you!

[acediac]

Originally Posted by Moupe

How is that silicone coolant pipe working out for you? Any signs of bulging or leaking?

Still unsure whether or not I buy the replacement BMW part or go with something aftermarket like what you purchased. I wish it was available in black instead of orange.

My coolant levels from both circuits have not dropped at all (after stabilizing over the initial few days) and the oil level has been spot on since I did this in November 2023. No leaks that I can see from anywhere and I've done 5000km / 3000mi since.

The oem connector pipe always fails at the plastic connector neck to the rigid pipe (mine did, and all the people posting on youtube show the same problem). One end is fixed to the engine which will move backwards and forwards but the other end is to the coolant tank which is fixed to the chassis, so there is continuous stress on that pipe. With brass connectors and a silicone pipe that is more flexible but stronger on the aftermarket replacement that I used, I think it is going to outlast the car. I highly recommend it if you are replacing that pipe. The colour is going to detract from the oem look but I think it's stylish, personally.

[acediac]

Originally Posted by angelforce

I wish I was your neighborhood to watch you doing this show!

I clicked on all the links but it seems the suppliers got out of stock fast. All of them are unavailable for me.

I will plan to do this upgrades soon.

Would be great if BMW had done that by design. (But it would mean less service for their workshops later after warranty hehe)

Thank you so much for this comprehensive manual.

I wish you had filmed that to sell as a course haha since I am not super savvy on this kind of work…

Just search Amazon for the part numbers and you will see alternate sellers. You can usually tell when some sellers are selling the same product since they use the same pictures.

Yeah, it would help if you have done things like replacing valve cover gaskets before. It's not for absolute beginners but not super difficult either, especially since I didn't have to disconnect the a/c gas as that would have been a pain. I had never done the vacuum coolant filling before but it didn't turn out too difficult once I got the tool with the right connectors (need coolant tank caps that fit perfectly and don't leak and that came in the kit that I bought.)

[f30jomi]

way more useful than any other resource i’ve come across. picked up my first new(ish) bmw and have to do this job myself. thank you for such a comprehensive guide! any update on how the aftermarket components and hoses held up?

[yehoshua]

Hey anyway to get in contact with you running into the issues u talked about about the dme failing and trying to trouble shoot it here the codes i got and a deive train malfunction this was after doing the water pump and housing thanks ?

[CincyBearcats]

Originally Posted by acediac

I used a vacuum kit (pictured below) to pump out the air from the low temp circuit and high temp circuit. You need to make sure there are two different sealing caps that fit the two reservoir openings.

Thanks so much for the very detailed description that you provided here. I just finished the removal of my OFH and am getting ready to install the new one once it is delivered. You tips and hints have been extremely useful.

I purchased the vacuum kit that you mentioned. Do you recall which caps you used for the two coolant circuits? The blue cap seems to fit the high temperature reservoir albeit very tightly, but I can't seem to find one that fits the low temperature reservoir.

Thanks again!!!

[acediac]

Originally Posted by yehoshua

Hey anyway to get in contact with you running into the issues u talked about about the dme failing and trying to trouble shoot it here the codes i got and a deive train malfunction this was after doing the water pump and housing thanks ?

Sorry I'm very late to the reply, I was not subscribed to the thread.

As described in my post, I had a similar thing happen with all the DME failing, it turned out that the plugs were not plugged in properly. You need to start each one with the latch horizontal, and when you push it down, the latch will come up vertical. Have to start from one end to another, so that the latch can be horizontal at first.

Once I re-plugged in all the DME cables, I could clear the error codes and the car was fine.

[acediac]

Originally Posted by CincyBearcats

Thanks so much for the very detailed description that you provided here. I just finished the removal of my OFH and am getting ready to install the new one once it is delivered. You tips and hints have been extremely useful.

I purchased the vacuum kit that you mentioned. Do you recall which caps you used for the two coolant circuits? The blue cap seems to fit the high temperature reservoir albeit very tightly, but I can't seem to find one that fits the low temperature reservoir.

Thanks again!!!

You should just compare the diameter of each cap and the inside thread with your radiator tank caps. They should be identical.

In my kit it was the green and red one. The inside should be simple, with no extra bits, otherwise I found it would leak. There is also a white one which seems to fit the low temp tank but the thread depth is smaller and the inside had extra flanges, I think that one leaked for me.

It is quite tight to screw on (just like the original caps), quite a few turns to get it all the way seated.

[acediac]

Originally Posted by f30jomi

way more useful than any other resource i’ve come across. picked up my first new(ish) bmw and have to do this job myself. thank you for such a comprehensive guide! any update on how the aftermarket components and hoses held up?

Again, a bit late in reply, but everything has been great. Done an extra 15k kms (10k miles) on it since, but no loss of coolant or oil, everything spotless.

[CincyBearcats]

Originally Posted by acediac

In my kit it was the green and red one. The inside should be simple, with no extra bits, otherwise I found it would leak. There is also a white one which seems to fit the low temp tank but the thread depth is smaller and the inside had extra flanges, I think that one leaked for me.

Thanks so much for getting back to me.

For anyone else trying this same kit... Strangely, I found that #17 (blue) and #20 (white) fit my high temperature reservoir and low temperature reservoir, respectively. The #17 has an internal protrusion, and I had to lubricate it with fresh coolant to get it to go on. The #20 is a simple version, as you mentioned. I found the white one (#20) to be a tighter fit than the green one.

This is the kit that I purchased off Amazon in the U.S.
"DAYUAN 28pcs Universal Radiator Pressure Tester Kit, coolant Pressure Tester kit coolant Vacuum Refill kit for Cooling System"
https://www.amazon.com/dp/B078RJT13X

Note: In the images below, the test caps are merely resting on the reservoirs. When actually in use, they thread completely onto the reservoirs. I just set them on there to take these photos.

[acediac]

Originally Posted by CincyBearcats

Thanks so much for getting back to me.

For anyone else trying this same kit... Strangely, I found that #17 (blue) and #20 (white) fit my high temperature reservoir and low temperature reservoir, respectively. The #17 has an internal protrusion, and I had to lubricate it with fresh coolant to get it to go on. The #20 is a simple version, as you mentioned. I found the white one (#20) to be a tighter fit than the green one.

This is the kit that I purchased off Amazon in the U.S.
"DAYUAN 28pcs Universal Radiator Pressure Tester Kit, coolant Pressure Tester kit coolant Vacuum Refill kit for Cooling System"
https://www.amazon.com/dp/B078RJT13X

Note: In the images below, the test caps are merely resting on the reservoirs. When actually in use, they thread completely onto the reservoirs. I just set them on there to take these photos.

Attachment 3525599

Attachment 3525600

Yeah I think there are all kinds of similar kits. As long as it fits the thread and seals properly and can hold pressure and fluid can pass through you should be ok.

[CincyBearcats]

Originally Posted by acediac

I just replaced the Oil Filter housing, water pump and cylinder head coolant line on my B48 and thought I would share my experience in case it helps anyone.

Thanks again to acediac for the excellent instructions. I'll add a few comments from my experience.

2017 F31 330i xDrive LCI with B46 engine, 70k miles (112k km)

Assumed the following common causes of coolant leaks on the B46/B48 engine in order of increasing difficulty

1. water pump
2. cylinder head to expansion tank hose
3. coolant connector from engine block to coolant hose
4. oil filter housing (OFH)

Diagnosis steps

1. I noticed a slow coolant leak on the garage floor just behind the front wheels and just left of center (driver side in the U.S.). The leak rate was roughly one or two drips per minute while the engine was hot.
2. I removed all the underbody covers. I found coolant residue on the front differential (xDrive), the transmission cooler, and the bottom edge of sound isolation foam located between the engine block and the component carrier (water pump and A/C pump). The U-joint on the front drive shaft had also slung coolant radially.
3. The cylinder head to expansion tank coolant hose had previously broken and been replaced under warranty at 44k miles, so I was pretty sure that it was not the source of the leak. Just to be sure, I removed the bracket on the top front of the engine which obscures the end of the hose where it attaches to the cylinder head. No coolant residue was found there.
4. After ruling out the cylinder head hose, I reasoned that the leak was likely one of the three remaining common causes (see list above). I first replaced the water pump because it was far easier than the other two (coolant connector and OFH). The leak remained.
5. Realizing that it was either the coolant connector or the OFH, I decided to replace both because they are so close to each other and prone to eventually leaking. I didn't want to replace one and have to do the entire job again a few months later when the other broke.
6. In the end, my leak was actually from the coolant connector.
7. Note: A coolant test/fill kit was extremely useful for diagnosing the location of the leak. I simply pressurized the system to 20 psi (140 kPa) and looked for leaks, which is far easier to do when the engine is not hot.

Comprehensive list of the parts that I replaced

• 11518638026 water pump - BMW brand from FCP Euro (included water pump pulley)
• 17129845173 cylinder head to expansion tank hose - silicone version with brass fittings; generic brand (Oikuda Plf) from Amazon
• 11118511205 coolant connector - aluminum version with gasket; generic brand (Link Lock) from Amazon (NOTE: Rein has an aluminum one listed on its website, but it is not yet available.)
• 11428596283 oil filter housing - aluminum version; Rein brand from FCP Euro (oil filter included)
• 11618637800 intake manifold gaskets - 4 BMW brand from FCP Euro
• 007603012110 washer for oil drain plug - BMW brand from FCP Euro
• motor oil - 6 liters Liqui Moly brand Special Tec LL 5W30 from FCP Euro
• 82141467704 coolant - 4 liters BMW brand
• distilled water - 4 liters

Comments on parts

• I try to use BMW/OEM parts whenever possible, but I used non-OEM parts for the three parts above because the OEM versions are known to fail. I would have preferred non-generic versions of the cylinder head hose and coolant connector, but none were available at the time.
• I did not replace the four torque-to-yield bolts on the upper strut tower brace (2 inner hex head and 2 outer E-Torx head). The BMW manual calls for them to be replaced and to be torqued to 56 N m plus an additional 90º. I re-used the four bolts and torqued them to 56 N m plus 45º (about where I could feel them begin yielding again). I will replace them later if necessary.
• I did not replace any of the gaskets on the air intake pipes or the throttle body despite the BMW manual calling for them to be replaced. Maybe that's a bad idea.
• I had recently replace the serpentine belt and tensioner, so I just re-used them. I would have replaced them otherwise.
• I debated replacing the component carrier along with the water pump. However, I had previously unbolted the A/C compressor from the component carrier when replacing the serpentine belt tensioner (an unnecessary step as I later learned), and it was a huge struggle to get the A/C compressor back onto the component carrier. It is an extremely tight fit, and it took me a couple hours to get it back together. Despite the risk of a future leak between the component carrier and engine block, I decided to forego this replacement. I searched online and did not find many instances of this being a source of a leak for other owners.

Specialty tools/supplies used

• coolant test/fill kit - "Dayuan 28pcs Universal Radiator Pressure Tester Kit, coolant Pressure Tester kit coolant Vacuum Refill kit for Cooling System" from Amazon (https://www.amazon.com/dp/B078RJT13X) - needed adapter #17 (blue) and adapter #20 (white)
• E8 1/4" socket (for transmission cooler, intake manifold screws, and other misc. screws)
• E10 3/8" socket (for OFH and intake manifold screws
• E8 1/4" flexible socket (for bottom screw on the wire harness bracket above the OFH and for the bottom screw on the transmission cooler) - "SUNEX TOOLS 9912 1/4-Inch Drive Universal External Star Socket Set, 1/4-Inch - 3/8-Inch, 9-Piece" from Amazon (https://www.amazon.com/dp/B003XIJ8K4)
• E10 3/8" flexible socket (for the bottom screw on the OFH) - included in kit above
• assorted 3/8" and 1/4" extensions
• 3/8" and 1/4" ratchets with flexible heads
• torque wrench that goes down to 6 N m
• dental picks
• CRC intake valve cleaner
• Permatex Ultimate Black RTV
• fabric gaffer tape

Notes on the steps required

• I followed every single step in the BMW manual (ISTA) except for one step: I did not remove the transmission cooler completely. I disconnected both coolant lines but did not disconnect the transmission fluid lines. I loosened but did not remove the three mounting screws. This was necessary to slightly shift the transmission cooler to the side for clearance of my 3/8" drive E10 flexible socket to properly engage the lowest screw on the OFH. If I had used a 1/4" drive E10 flexible socket instead, I probably would not have needed to shift the transmission cooler at all (nor remove the fuel line bracket next to the transmission cooler).
• The bottom screw on the wiring harness bracket (just above the OFH) was difficult to remove and even more difficult to install. A flexible socket was extremely helpful.
• The bottom screw on the transmission cooler was difficult to loosen. Removing the fuel line support bracket was necessary. I accessed all three screws on the transmission cooler from below.
• In my opinion the bottom screw on the OFH was easier to remove than the other two difficult screws listed above. Once I loosened the transmission cooler and shifted it slightly to the side (1/8" or so), I was able to get to the screw pretty easily. I wrapped a piece of tape around the flexible socket to make it a little stiffer. I was able to get a direct line of sight to the screw from above by looking almost straight down on it. I had to tape the wiring harness to the side.
• I took tons of photos as I went and repeatedly referenced them during re-assembly, particularly when re-routing all the cables and hoses to their original paths.
• When reconnecting the digital motor electronics (DME) control unit, I started at the rearmost connection and worked forwards. The connectors are all keyed such that they cannot be reconnected in the incorrect spot. I made sure they were fully seated by pressing downward until the lever lifted on its own. Once all of them were connected, I double checked that they were all seated correctly by inspecting the bottom edge of every connector. The bottom edges were all aligned.
• While working, the factory fabric tape on many of the wire bundles came off. Most of the time, I didn't bother replacing it. Occasionally, however, I used some gaffer tape to protect wires near sharp edges.
• I used a very thin layer of black RTV on the gasket included with the aftermarket coolant connector.
• With the intake manifold removed, I took the opportunity to clean the intake valves. I did not have access to walnut blasting equipment and did not want to invest in it. Instead, I meticulously cleaned the valves with dental picks. This was tedious and took a long time. It was far from perfect, but I figured it was better than nothing. Once I was finished with the dental picks, I submerged each valve in CRC Intake Valve Cleaner and let them soak overnight. I extracted the cleaner by taping a section of vinyl tubing to my shop vacuum.
• This was the first time that I used a coolant test/fill kit, and I regretted that I had not purchased one sooner. First, it was extremely helpful for diagnosing the leak. More importantly, it made the refilling and bleeding process much, much easier. After using the vacuum pump to fill the two coolant systems, I ran the vehicle's built-in bleed cycle on each system separately (low temperature first, high temperature second). In both cases, I needed to add just 100 ml or so of additional coolant. In the past, I had needed to run the bleed cycles multiple times. Once the two systems were full of coolant and properly bled, I pressurized both systems to 20 psi (140 kPa), which is the pressure rating of the reservoir cap. I waited 30 minutes and checked for leaks before re-installing all the underbody covers.
• Miraculously, I did not have a single CEL or engine code (full test with ISTA) when starting the engine for the first time after I was complete. This was despite have the entire DME sitting on my workbench at one point. I couldn't believe it! It's a testament to the benefit of following each and every step in the ISTA procedure.

location of the leak on the coolant connector


before replacing parts


after replacing parts


after cleaning intake valves

[acediac]

Originally Posted by CincyBearcats

Thanks again to acediac for the excellent instructions. I'll add a few comments from my experience.

Excellent work, sir. Sounds like you had a very similar experience to mine.

Isn't it amazing BMW continues to use that plastic piece bolted onto the engine block? (not to mention the rigid (!) coolant pipe between an engine that moves and a tank that doesn't)

As I mentioned, that component carrier where the water pump bolts onto has a gasket that seems to be formed from Loctite 5970 silicone in the interface to the engine block, even in the new genuine part that I bought (for $$$). (I wish I took photos) It *should* be ok, but if it leaks at least you will know what to do now!

One suggestion for cleaning the intake valves is to use brass gun barrel cleaning brushes to avoid scoring the back of the valves. Need pretty long and thin ones which can bend, though. Best to use the walnut shells as recommended by BMW of course. I was going to do mine, but I ran out of time. Mine didn't look too bad though.

One thing for sure, I don't think either of us will ever have OFH and coolant connector issues again!

PS. oh yeah, I would still check the coolant levels over the next few weeks, as my experience suggests it will need to be topped up.