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Hi folks, new user here, I've had a 2004 e46 automatic for about a year now, first car, & I've been chasing cooling leaks n issues ever since :). Skip to bottom if you want to go straight to my question. But here's context:

I did a cooling system overhaul when my temp sensor got stuck open, used this kit from fcp euro: BMW Cooling System Overhaul Kit With Water Pump - E46COOLKIT
Everything went smoothly and now my e46's temp needle stays right on the middle. Thanks to you guys for the advice I got prowling this forum.

But, even after the overhaul, I found my coolant levels dropping still, but only during/after long drives.
I would check the car cold, over a few days of no driving, and the coolant level would be perfectly topped up. But checking the coolant levels after a couple long drives, the coolant level stick would sink to the bottom. Even had the low coolant light come on a couple times while I was far from home (good thing I've learned to keep a jug of 50/50 in the trunk).

Long story short, today I went for a hard drive and and put the thing up on a ramp after while it was still hot. Then, I saw a ton of coolant spilling out of this bottom hose which connects to the same bottom mounting bracket that the Expansion tank sits on.

It was weird-- at first, I turned the car off, didn't see too much dripping. Then, a huge flow came from this hose. Then it slowed to a drip, then stopped. I guess it's something to do with pressure and coolant flow, I don't know LOL.

This hose seems to connect from the mounting bracket attached to the radiator & expansion tank. Then it heads back up towards the engine, connecting to another hose. Not 100% confident what this hose is, it wasn't replaced in the cooling overhaul kit.
But from looking around, my best guess is that it's the coolant return hose, #5 here:

918720


Unfortunately there's no videos I could find, and few posts re: replacing this hose.

I'm wondering if anyone could help me confirm if this is indeed the coolant return hose, & that I need this part #11531705210? I wanted to make sure if I could, before I start buying parts.

Also, anyone have any experience/tips doing this repair?

I've read this hose is hard as hell to pull out, and there's a risk of damaging the other pipe it's connected to closer to the engine, which scares me as an amateur.. don't wanna risk breaking that other pipe as it looks way harder to reach..

Any thoughts are appreciated
 

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It was weird-- at first, I turned the car off, didn't see too much dripping. Then, a huge flow came from this hose. Then it slowed to a drip, then stopped. I guess it's something to do with pressure and coolant flow, I don't know LOL.

This hose seems to connect from the mounting bracket attached to the radiator & expansion tank. Then it heads back up towards the engine, connecting to another hose. Not 100% confident what this hose is, it wasn't replaced in the cooling overhaul kit.
But from looking around, my best guess is that it's the coolant return hose, #5 here:

View attachment 918720

Unfortunately there's no videos I could find, and few posts re: replacing this hose.

I'm wondering if anyone could help me confirm if this is indeed the coolant return hose, & that I need this part #11531705210? I wanted to make sure if I could, before I start buying parts.

Also, anyone have any experience/tips doing this repair?

I've read this hose is hard as hell to pull out, and there's a risk of damaging the other pipe it's connected to closer to the engine, which scares me as an amateur.. don't wanna risk breaking that other pipe as it looks way harder to reach..

Any thoughts are appreciated
1) make sure no homeless man hiding under the intake manifold and releasing his stress. LOL.
2) You're right, it's #5 hose for returning the tank coolant back to the pump. Remove the air filter and you should be able to reach to the hard pipe and disconnect/replace it.

Always use some silicone grease (brake grease) to lube the hose connector O-ring and the male counterpart for ease of install/removal.
 

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Always, please expound.
 

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Discussion Starter #4
1) make sure no homeless man hiding under the intake manifold and releasing his stress. LOL.
2) You're right, it's #5 hose for returning the tank coolant back to the pump. Remove the air filter and you should be able to reach to the hard pipe and disconnect/replace it.

Always use some silicone grease (brake grease) to lube the hose connector O-ring and the male counterpart for ease of install/removal.
You're right, I did indeed find a small homeless man under my intake manifold taking a piss, explaining that drip pattern

Thanks though sapote, given your confirmation that #5 is the hose in question, I've ordered the new hose.. will update when it comes in & I try the repair 🙏
 

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Be careful. You have to remove that hose from the cooling hard pipe. They are fragile and can break easily. If you break the hard pipe then you have a lot more work to do including removing the intake manifold.
 

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Be careful. You have to remove that hose from the cooling hard pipe. They are fragile and can break easily. If you break the hard pipe then you have a lot more work to do including removing the intake manifold.
The old pipe could easily break at the pump mounting hole if it was disturbed, but it won't at the hose connection. As long as the 2 mounting 13mm bolts untouched, then rest of the pipe is strong as new.
 

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If you yank on the hose you can move it enough to crack the hard pipe where it connects to the engine. The bracket that holds the pipe in plce is not that strong. You can bend it with your hands. The best way is to try to twist the hose a little bit back and forth without pulling the hard pipe in any direction.
 

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I have a preface lift M52 engine and my hard pipe and connector hose is not keyed. I just replaced the hose. It does have a locking tab that must be pulled out.
 

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I have a preface lift M52 engine and my hard pipe and connector hose is not keyed. I just replaced the hose. It does have a locking tab that must be pulled out.
All of these connectors are keyed. I love to see one that has none.
Without being keyed, the locking tab or clip could become useless; think about this young man.
 

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My connector hose did not come off until I twisted it back and forth and wiggleed it in a circular motion (clockwise and them counter clockwise). That is what finally loosened it. You need to break the mated surfaces. Just going in and out or side to side did not do it.
 

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My connector hose did not come off until I twisted it back and forth and wiggleed it in a circular motion (clockwise and them counter clockwise). That is what finally loosened it. You need to break the mated surfaces. Just going in and out or side to side did not do it.
I just ran out to my garage to look at these parts:
2 different hard pipes both have key on the male connector.
One upper hose with 2 female connectors at its ends both have keys.

Unless you had bought all the parts from the same manufacture with keyless connectors, it's hard to imagine how one design (keyless hose) can connect to a keyed design (keyed thermostat male connector).

show us a pic of keyless female connector (don't show us a keyless male connector as it could easily be removed).
 

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The push pull method did not work for me so if the OP has trouble removing the hose, try working it in a circular motion e.g. like removing a fence post from the ground. You can try to push it in and then pull it straight out. That doesn't usually work. Then try rolling and twisting the post in a circular motion and the fence post will come up much easier because you've broken the mating surfaces. Just stating what did and didn't work for me and I just did this repair.
 

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The push pull method did not work for me so if the OP has trouble removing the hose, try working it in a circular motion e.g. like removing a fence post from the ground. You can try to push it in and then pull it straight out. That doesn't usually work. Then try rolling and twisting the post in a circular motion and the fence post will come up much easier because you've broken the mating surfaces. Just stating what did and didn't work for me and I just did this repair.
I don't believe it can be turned in circular motion. Show us a pic of no key female connector!!!

I never had trouble disconnect these connectors - used some silicone grease on the mating parts before install, and pull or pry both sides (180 degrees apart) evenly and steady, it will slowly separate.
 

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Sapote, I will really try to dumb this down for you. It tried the methods you mentioned and they did not work FOR ME. I wasn't until I applied torsional force that the hose came loose. You weren't with me when I did it so you have no idea what I did. I have remove many coolant hoses this way. I would never be so presumptuous as to tell you what you did especially if I wasn't there to witness it. You can tell the OP what YOU did, but don't try to tell the OP what I did, and i will do the same for you.
 

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Sapote, I will really try to dumb this down for you. It tried the methods you mentioned and they did not work FOR ME. I wasn't until I applied torsional force that the hose came loose. You weren't with me when I did it so you have no idea what I did. I have remove many coolant hoses this way. I would never be so presumptuous as to tell you what you did especially if I wasn't there to witness it. You can tell the OP what YOU did, but don't try to tell the OP what I did, and i will do the same for you.
I don’t question what you do, but I asked to show us a picture of a female connector with out key.

Which particular hose you had a hard time with?
 

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Discussion Starter #18
Update: Just had a sunny day and was able to do this repair.

Soaked the hose connection points with an ungodly amount of silicone lube as recommended.

The end connecting to the expansion tank base came out easy. The other end felt glued tight.
I went slow and light and gradually kept tugging harder to ease the hose out bit by bit. Did around 7 cycles of blasting lube, then pulling, lubing, pulling, repeat (lol). Eventually slid out out w/ no damage done to the hard pipe 🙏 🙏

With the hose out, I saw the o-ring on the end connecting to the expansion tank base must've been the issue. The o-ring was just crazy swollen, 2x the size of the replacement hose's o-ring. Replaced the hose, went for a long drive, and came back to see no dripping & no coolant loss. Thanks guys... after months of buying coolant jugs and chasing leaks, this looks to be a success :)

RE: this circular motion vs. keyed connector fiasco, I found that my hose was indeed keyed, would only go straight in/out. That's not to say trying to turn in a circular motion didn't help me get the hose out... it's hard to say because I tried everything. Tried pulling it straight out, wiggling it side to side a bit, tried twisting it a bit. But eventually, just a ton of lube & pulling it straight out did the trick.
 

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Update: Just had a sunny day and was able to do this repair.

Soaked the hose connection points with an ungodly amount of silicone lube as recommended.

The end connecting to the expansion tank base came out easy. The other end felt glued tight.
I went slow and light and gradually kept tugging harder to ease the hose out bit by bit. Did around 7 cycles of blasting lube, then pulling, lubing, pulling, repeat (lol). Eventually slid out out w/ no damage done to the hard pipe 🙏 🙏

With the hose out, I saw the o-ring on the end connecting to the expansion tank base must've been the issue. The o-ring was just crazy swollen, 2x the size of the replacement hose's o-ring. Replaced the hose, went for a long drive, and came back to see no dripping & no coolant loss. Thanks guys... after months of buying coolant jugs and chasing leaks, this looks to be a success :)

RE: this circular motion vs. keyed connector fiasco, I found that my hose was indeed keyed, would only go straight in/out. That's not to say trying to turn in a circular motion didn't help me get the hose out... it's hard to say because I tried everything. Tried pulling it straight out, wiggling it side to side a bit, tried twisting it a bit. But eventually, just a ton of lube & pulling it straight out did the trick.
1) O-ring will be swollen again unless you stop the ATF leak from the steering reservoir soon. Either the cap leaks or the 2 hoses clamps need to be tighten. Temporary you can make paper towel balls and insert them tightly between the said hoses (under side) and the alternator or the tank, whatever near the hoses to collect the leaking ATF.

2) Thank you for confirm the keyed connector. The most effective motion is wiggling it side to side.
 

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Glad you got the hose off. Since the cooling system is the weak link in these engines and this hose can be difficult to remove, I bet this is of interest to many. I had a really hard time with it. Mine seemed like it was glued on. The application of an ungodly amount of silicone was a good idea. Trying to pry it off can result in gouging the hard pipe if you are using a pick. So its good that you didn't try that. I tried pulling it straight out and side to side and up and down at first but it didn't work. It was like a Chinese handcuff. Wiggling it in every direction eventually did it for me as might have done for you. This is a repair that is probably fairly common and a good post.
 
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