[RayLivingston]

I just finished (I thought) doing a bunch of PM on my '07 335i sedan. I replaced the valve cover, the serpentine belt, idlers, and tensioner, and the oil filter block gasket. All that went just fine, but when I put it back together, and topped off the coolant, the coolant I added started pouring out the bottom of the exhaust side of the engine. There is ZERO visibility in the area in question, but the leak appears to be above where the plastic inlet air duct that runs across the front of the engine connects to the front turbo, and it seems to be draining directly from the overflow tank, down onto the aluminum cross-member. It appears to be coming from ABOVE all the hoses in that area.

I am totally baffled, as it never leaked a drop before, and I was not working in that area at all. The only thing I can figure is I must have bumped something that broke one of the many lousy plastic parts, which have been the bane of this cars existence. Seems like every time I open the hood, another plastic part breaks (unlike my '01 e46, which still has virtually ALL of it's original plastic parts after 18 years/220K miles).

Are there any good diagrams or photos of that area, showing what's in there? How do I even get access? Just removing the plastic air duct and the looooooong aluminum intercooler duct that runs over that area looks like a nightmare.

Help!

Regards,
Ray L.

[gbalthrop]

Originally Posted by RayLivingston

...'07 335i sedan...when I put it back together, and topped off the coolant, the coolant I added started pouring out the bottom of the exhaust side of the engine. Are there any good diagrams or photos of that area, showing what's in there?

Attached is a Coolant Flow Diagram from BMW Training Manual, and also a list of E9x references. Particularly helpful are Bentley (searchable pdf) and TIS. I don't have a 335 so can't suggest a likely suspect, but basically it's just a matter of getting familiar with all the hoses & connectors and tracing the flow diagram on your particular car.

BTW, what's with the jpg attachments function?
What edits to jpg files to keep from screwing up the width?
These are ONLY 92 & 179 KB screenprints pasted to Paint &
Saved As jpg

Please let us know what you find,
George

[jwalker87]

If it's above that inlet air duct, I think the only thing up that high is the reservoir itself. My 2011 335i had the reservoir fail, but that was a small leak only noticeable when the system was pressurized. If it's pouring out as you say, I would imagine it has to be the hose disconnected. It's one of those plastic-end-and-metal-clip affairs. I would make sure the hose is actually seated, and if that's not the culprit, maybe remove the reservoir itself to get a better view of the area.

Best of luck! And agreed on the e90 plastic cooling system parts - I have now been stranded by one of mine on 3 separate occasions, all of them cooling system related.

[RayLivingston]

Those diagrams will be a HUGE help! Thanks!

All the hoses, and the reservoir are leak free, to the extent they are visible. The radiator also is leak-free. The leak is coming from somewhere on the right side of the engine, several inches rear of the timing cover. The reservoir is brand-new, as is the lousy plastic pipe that runs across the cross member, and several of the hoses. All but the reservoir were replaced about a month ago, and have not leaked a drop. The coolant is dripping from well above all that stuff, which is the baffling part. What the heck is up that high that carries coolant, other than the engine itself. There were NO leaks before I replaced the valve cover, and belt idlers and tensioner. I never got within 12 inches of where the leak seems to be.

Looks like I'll need to drain the radiator, and remove some hoses just to get a look at what's in that area.

Regards,
Ray L.

[Bamaben]

Disconnect the expansion tank mounts and look under it. I replaced my tank as part of PM because they'll leak at that top seam. At least you may can see better with it out of the way. There are coolant lines running to the turbos.

[RayLivingston]

The leak appears to be the thermostat, or one of the two hoses connecting to it from the front. I was able to see coolant dripping down onto the front cover of the water pump, and I don't see anywhere it could possibly be coming from other than the thermostat or those two hoses. Now the trick is getting in there enough to pin down the exact source, without this turning into a major project.

If anyone knows:

1) How do you remove the plastic air duct that runs across the engine to the front turbo inlet? I can easily disconnect the end on the other side of the car, and the two bolts holding it to the front of the engine, but does it then just pull off the turbocharger (once all the coolant hoses are out of the way)? It appears to me the hard line for the A/C evaporator would prevent it from coming off.

2) How do you remove the hard duct that runs from the intercooler to the two turbo outlets? I can get the clamps off without too much grief, but it does not appear to me there is enough room to get the duct out, even once it's all disconnected.

3) Should I need to remove the thermostat, it appears to me it requires:
i) Remove (front) large, snap-on hose to radiator
ii) Remove (top) small, snap-on hose to plastic pipe running along cross-member
iii) Remove (rear-lower) screw-clamp hose to water pump
iv) Remove (rear-upper) screw-clamp hose to ???? - What does this one connect to??
v) Unplug electrical connector
vi) Remove two bolts from bottom of water pump to release thermostat

Is it necessary to drop the rack or anything to make room to get it out?

Regards,
Ray L.

[jwalker87]

You want to go from the bottom side if you're getting at the thermostat and/or water pump. Especially on a RWD model, they are fairly easily accessible once you jack the front of the car up and remove the plastic undertray.

Here's a DIY thread that has all the steps to get to those components. Considering the sheer number of coolant connections on these two components, a leak is fairly likely. I didn't bring it up at first because of the "high-up" nature of the leak you were describing.

https://www.e90post.com/forums/showthread.php?t=784416

[gbalthrop]

Originally Posted by RayLivingston

The leak appears to be the thermostat, or one of the two hoses connecting to it from the front...Now the trick is getting in there enough to pin down the exact source, without this turning into a major project.

TIS online service manual has good procedures & diagrams on most projects. Here is Removal of Thermostat on N54:
https://www.newtis.info/tisv2/a/en/e...lines/1LXyJD0x

There are pages on related procedures you should check for ideas on what else is in the area.

George

[Psyphertext]

Originally Posted by gbalthrop

Attached is a Coolant Flow Diagram from BMW Training Manual, and also a list of E9x references. Particularly helpful are Bentley (searchable pdf) and TIS. I don't have a 335 so can't suggest a likely suspect, but basically it's just a matter of getting familiar with all the hoses & connectors and tracing the flow diagram on your particular car.

BTW, what's with the jpg attachments function?
What edits to jpg files to keep from screwing up the width?
These are ONLY 92 & 179 KB screenprints pasted to Paint &
Saved As jpg

Please let us know what you find,
George

Makes me miss pre-1990's Ford and GM.

[RayLivingston]

Well, this is annoying. After removing the thermostat, testing it, and checking all the hoses, I finally found the culprit. But, nowhere near where I expected. The O-ring on the bypass hose (the one that "plugs into" the head, next to the oil filter block) had failed. Apparently, the coolant managed to run down, and across, the front of the engine, and drip onto the water pump, making me think the leak was somewhere near the water pump. Even when it was leaking, I could NOT see anything on the front of the engine. This was not helped by the fact that the front of the engine started out wet with coolant, since I had to remove several of the hoses to do the other work I was doing.

Anyway, I removed the thermostat for nothing. However, I'm not TOO sorry I did it, as I can now be reasonably confident everything over there is ok. The thermostat had been replaced (by the PO), though they put it back with all the clamps in completely inaccessible positions. I replaced it with the clamps where they are all easily accessible. Should I ever need to replace it again, it'll be an easy job.

Thanks for the help!

One new problem, however, which I'll put on a new thread...

Regards,
Ray L.

[jwalker87]

Great that you found the culprit! That connection is one of the ones that stranded me; the whole plastic connector grenaded while I was driving down the road about 20 minutes from home. So it could have been worse.

[arkie6]

That plastic hose connector on the front of the head failed on me not too long ago. In my case it completely sheared off, so it was easy to see the source of the leak. I replaced just that plastic fitting with a machined aluminum fitting from ebay.

[RayLivingston]

Originally Posted by arkie6

That plastic hose connector on the front of the head failed on me not too long ago. In my case it completely sheared off, so it was easy to see the source of the leak. I replaced just that plastic fitting with a machined aluminum fitting from ebay.

Great idea!! And I have two CNC mills, so I can easily make my own in a few minutes!

Regards,
Ray L.

[arkie6]

The N54 aluminum hose fitting is $13.88 with free shipping on ebay:

[arkie6]

This weekend I also replaced the upper and lower radiator hoses and the hose from the upper radiator hose to the reservoir because these hoses have plastic fittings similar to the one that failed earlier. It turns out that I made a good decision because as soon as I tried to unclip the reservoir vent hose that runs along the top of the fan assembly, the plastic middle part of the vent hose broke with very little pressure applied and then the plastic nipple on the upper radiator hose broke off. The rubber hoses appeared to be in good shape, but the plastic parts of the hoses had significantly degraded. The upper radiator hose plastic fittings were the worst shape because they see the highest temperature water from the engine. The lower radiator hose that connects the radiator to the electric water pump wasn't in that bad of shape because the water is cooler by the time it reaches that hose. I got lucky and caught this before it failed on the road. My car is 10 years old with 110,000 miles. If you search the forums, you will see that this is a fairly common failure after the cars get some years and miles on them.

[Bali]

Originally Posted by RayLivingston

(unlike my '01 e46, which still has virtually ALL of it's original plastic parts after 18 years/220K miles).

That is living on borrowed time, my friend.

[RayLivingston]

Originally Posted by BaliDawg

That is living on borrowed time, my friend.

Not really. The important things have been replaced - hoses, etc. On the E90, EVERYTHING plastic is failing. Plastic fasteners, plastic hose clips, plastic pipes and ducts, plastic connectors, the fan shroud, the cabin air filter housing, etc. etc. Most of those things are just fine on the E46, despite being almost twice as old and more than twice the miles. MUCH better quality parts on the E46.

Regards,
Ray L.

[gbalthrop]

Originally Posted by RayLivingston

...On the E90, EVERYTHING plastic is failing. Plastic fasteners, plastic hose clips, plastic pipes and ducts, plastic connectors, the fan shroud, the cabin air filter housing, etc. etc. Most of those things are just fine on the E46, despite being almost twice as old and more than twice the miles. MUCH better quality parts on the E46.

OR -- MUCH more heat under hood on N54 turbo 335i?

George

[RayLivingston]

Originally Posted by gbalthrop

OR -- MUCH more heat under hood on N54 turbo 335i?

George

Doesn't seem so, but could be. But that is a really good reason to use different/better plastics, or metal. Bottom line is the E90 is falling apart FAR faster than the E46, and every time I work on it, ancillary things end up breaking. The little "press-to-release" rings on nearly all of the intake and vacuum hose and pipe fittings have broken off, just from pressing normally to release them. Haven't had a single one break on the E46, despite being twice as old, and twice as many miles. First time I moved the little hose that goes fro the upper radiator hose to the coolant overflow tank, the little fitting broke off the radiator hose, even though I barely touched it. Everything is just brittle as he11.

Regards,
Ray L.

[soulcrusher]

Glad you found the leak. I was looking at the diagram to relate how my coolant is leaking by the ignition system. Any thoughts? I attached an image with two blue arrows edited to where coolant was leaking and fizzling out. Currently its DI water since I am flushing the system, no oil residue was seen.

At the same time, the expansion tank decided to leak but that was easily identified. The other described leak is confusing.