My advice would be getting the front end off the ground and removing the under shields. They could be hiding where it's coming from. Once the car is there, start filling the system with distilled water and watch the car leak.

You could also try some UV Dye in the coolant, then using a black light to determine the source of the leaking. I'd be guessing that its either the upper radiator hose or the plastic end tanks of the radiator. I also believe the radiator petcock is on that side as well.

Good luck and Happy wrenching!!

 

Rent or buy or build a pressure tester. That's a sure way to find the leak faster. Remember when your engine was running, there's pressure in the cooling system thus easier for coolant to leak out. Once your engine cools down, there's less pressure in the cooling system thus making it that much more difficult to find the leak.

You can touch, feel, and see your car. No one else on this forum can do that. You're the best person to find the leak. Everyone on this forum would be just guessing. Good luck.

 

Rent or buy or build a pressure tester.

Why go through the trouble of buying, building or renting a kit when you literally said the engine produces its own pressure. In the same paragraph, none the less.

It would be easier to fill the system with cheap water and turn it on for a 60 seconds and doesn't require driving to a parts store for a kit. Especially with such an egregious leak.

You are correct though, we do not have access to the vehicle and anything we say will be guess made on readily available information.

 

INDEED! . Truth be told; heater inlet is due to be replaced ANYWAYS. Upper and lower hose including the radiator was recently replaced. Mechanic is coming tmw with the tools for diagnosis and I'll do the rest.

 

If you have your own tools like any standard set with 80-120 pieces, you could do this yourself. If you got the funds get the mechanic though.

 

Take a good look at the radiator outlet temperature sensor in the lower hose.
The O-ring often leaks and can be replaced.
I believe this is the part number
O-Ring Seal For Coolant Temperature Sensor
13621433077S O-Ring

 

That is because an idling engine with the coolant at 96 degC produces less than 1 bar of pressure (that's 1 bar of gauge pressure, not absolute). Yes, this is true. Look up water P-T diagram.

Then why on the next morning we hear the hissing noise of air sucking in when crack open the 2bar cap? Assuming same ambient temp on both days.

 

I think you’re misunderstanding. With a hot idling engine (96 deg C), the cooling system produces less than 1 bar of GAUGE pressure, which is over and above normal atmospheric pressure. Please look up P-T diagram of water. I don’t make up physics or thermodynamics.

 

don’t make up physics

Unless you're into quantum string theory. That's all made up 🤣

 

I am going to replace all hose with silicone. They last a long time.

 

The OE hoses have much better fitment, are cheaper, and last a good long time.
Do your research first. Most E46 silly-cone hoses we’ve seen have bad fitment (looking at you, Morimoto).

 

One more thing: e46 A/C doesn't use antifreeze coolant, correct?

 

Hahaha, what? AC uses refrigerant, not coolant.

 

Hahaha, what? AC uses refrigerant, not coolant.

Just making sure.. since the coolant leak is on the passenger side. Thanks. I'm learning .

 

A coolant pressure tester is cheaper to buy than you might imagine ($45 open box here) and also more useful than you may think. Examples - when doing a full cooling system refresh, I use mine to test for leaks before putting any liquid in the system. I've found a few leaks by listening for hissing air that way. When you replace all three million hoses at once, chances are one might not be seated correctly, etc. Moreover, as someone else mentioned, being able to get your hands into tight spaces on a cool engine to figure out the source of the leak makes things a lot easier. I cannot recommend just investing in one enough, especially now that they are so darn cheap.

In addition to @Bali's on-point warning about fitment issues with non-OE hoses, silicon hoses also suffer from a lot more coolant loss via osmosis than rubber ones. You will need to check and top off your coolant regularly. Expect significant losses. Silicon is not necessarily an upgrade. Rubber hoses last a very long time and in my experience, the o-rings on the quick-connect fittings tend to fail and leak way before the actual rubber hoses do.

 

One more question, I have been trying to search this on the internet and YouTube with no avail. Is this the correct terminology: long coolant return hose as shown on the diagram?

I need to know the name so I can order that particular part. I'll try realoem, but much appreciated for the help here.

RealOEM.com - Online BMW Parts Catalog

I checked the picture and it's the same as above, I couldn't find the one I marked above. Any assistance would be appreciated. I tried heater and A/C section, no luck.

 

The BMW part number is what you need to order/verify correct part, not necessarily the description.
part #8: 11537502525

 

That's a hard pipe, not a hose. #8 and #6 are hard pipes underneath the intake manifold. Don't go by name, search for the part number.

 

The BMW part number is what you need to order/verify correct part, not necessarily the description.
part #8: 11537502525

I am referring to this picture:

That wasn't included in my package I ordered, so I just want to replace the whole hoses. My car is at 130k miles. This is the particular hose I am looking for, hence it doesn't show on realOEM part, where you hightlighted the yellow part. Sorry if I wasn't being clear.

 

Okay, I think that this kit has every single hose in the cooling system. Maybe go through, match up the part numbers with what you have, and via process of elimination you can figure out which hose it is?

RealOEM shows this heater hose diagram, but it is quite confusing and I am not sure which hose is the one in your picture. I know I replaced this in my E46, but I ordered a kit and just matched everything up.

Edit: I think it might be 64218376999. Is there a hose clamp that connects to the aux water pump on the other side?

 

BMW Heater Hose - Rein 64218376153

BMW Heater Hose - Rein 64218376153

www.fcpeuro.com

is this the correct context I’m referring to?It looks very sturdy so no need to replace it? It’s related to coolant leak. I’ll do troubleshooting to find it; upper and lower radiator hoses are already replaced including the radiator - replaced it like a year or two ago. Mechanic did warn me that heater inlet is about to burst. So.. I’ll find out this weekend.

 

BMW Heater Hose - Rein 64218376999

BMW Heater Hose - Rein 64218376999

www.fcpeuro.com

Do the other 2 heater hoses while you're in there.

 

Just my two cents - you have the intake manifold off. Replace everything. Can you imagine how annoying it would be if you skipped replacing that hose because it "looks sturdy" and a few days later, it started leaking?
Those coolant hard lines also should be replaced at this point. They have a propensity to crack and leak and cannot be accessed without removing the intake manifold.

 

Found the diagram:

Thank you, guys! I GOT EM! :roll up sleeves: time for stage 2 cooling system bitches!

For BMW E46 320i 330xi HVAC Heater Outlet To Expansion Tank Hose Rein Automotive
For BMW E46 320i 325Ci 330i 330xi HVAC Engine To Heater Valve Inlet Hose Rein

Expansion Tank Hose
Engine to Heater Valve Inlet

I am trying to find Heater Valve Inlet to Heater Outlet... missing one more part:

I believe this is the correct one which I am referring to?

REIN Engine Coolant water Hose Heater Valve to Heater Core For BMW E46 3 Series | eBay

NOTE: Heater Water Hose - Heater Valve to Heater Core. (1) New Heater Water Hose for BMW. Make Model Year BodyType Engine. All Engines.

upto.site

EDIT: nevermind, got it. Anyways, thanks for your help again!

 

I have the same year/model car and when mine had that leak it turned out to be the hard coolant lines under the manifold (#8 and #6 I believe from the realoem photo you have posted). If these have not yet been replaced, it's a good idea to do so. The hoses busted right as they entered the block and required the use of tweezers to get to the broken bits. At the time I did the work on my car, I replaced a sensor, the starter and cleaned the heck outta that engine just because once that manifold is back on, I certainly don't want to do that job again!

 

I have the same year/model car and when mine had that leak it turned out to be the hard coolant lines under the manifold (#8 and #6 I believe from the realoem photo you have posted). If these have not yet been replaced, it's a good idea to do so. The hoses busted right as they entered the block and required the use of tweezers to get to the broken bits. At the time I did the work on my car, I replaced a sensor, the starter and cleaned the heck outta that engine just because once that manifold is back on, I certainly don't want to do that job again!

I hear ya.

 

Found the real problem. Something fell inside, some kind of plastic pipe, and the serpentine belt grinded it pushing against lower radiator hose; so I tested the lower radiator hose and notice something off, loose, and wet. That's the culprit. I cannot pull out the broken plastic pipe... I may have to pull it out underneath my car but I can't do that since the road is uneven. See pix:

What's the hell is that thing? I can only surmise it fell off the alternator pipe of some sort? Ah, it's called lower alternator cooling duct. That's what fell off the alternator and the serpentine belt grinded it against the lower hose radiator - lower duct has a single big HOLE on it. Upper alternator duct is also missing. Diagnosis complete and documented. Solution pending.

Found the diagram:

The only possible solution is the remove the bottom radiator hoses to get that alternator duct pipe out. Right now it's raining so I will do that early tmw morning.

During repair, mechanic removed alternator air duct | E46 Fanatics Forum

 

Return hose connector (to the radiator) is impossible to budge; I took the pin off and still having difficulties taking it off. Ideas? I tried prying it off with a big flathead screwdriver, didn't work. lol...

EDIT: tried all my might.. . I think the K-SEAL might be the culprit here. However, the mechanic replaced my radiator a couple of years ago so it shouldn't be an issue. Maybe it's K-SEAL residue on the return hose connector - not sure tho.

 

Do I have to remove the radiator bracket in order to remove water hose connector (see pix below)?

Or do I just go ahead and remove the expansion tank first, automatic transmission cooler, and then remove the water hose connecter? I wasn't sure if the lock mechanism would prevent me from removing it. Thanks! I have been scouring YouTube videos for answers. I just need to replace the return hose connector.

 

Hi,
I like to disconnect the hoses, remove the sensor from the tank. The fan should be off, use a screw driver to pry the latch for the bracket holding the tank on to the radiator and slide it up. Not sure how different the auto is over the manual so I put this for you to use as reference. Radiator Anatomy .

To be honest when I remember that part of my bracket can separate with the expansion tank from the rest of the radiator and it slides back into place with these discrete groves along the radiator bracket that is on the radiator.

 

Hi,
I like to disconnect the hoses, remove the sensor from the tank. The fan should be off, use a screw driver to pry the latch for the bracket holding the tank on to the radiator and slide it up. Not sure how different the auto is over the manual so I put this for you to use as reference. Radiator Anatomy .

To be honest when I remember that part of my bracket can separate with the expansion tank from the rest of the radiator and it slides back into place with these discrete groves along the radiator bracket that is on the radiator.

Thanks for the response. I am just curious if I can remove the water connection hose after removing the expansion tank? How do I remove the water connection hose (as shown on the picture above)? That's the answer I am seeking, many of the YouTube videos didn't even cover the water connection hose removal part . I have automatic.