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Discussion Starter · #1 · (Edited)
UPDATE: So I thought the problem was coolant leak from the thermostat. Drops of white coolant residue still coming back. May be the two plastic coolant pipes under the intake manifold....still troubleshooting.

2000 528i
I notice a white residue on my air box and power steering reservoir after driving (bottom photos). I found what I think was the source in a spot on the underside of the upper rad hose connection and so I replaced the thermostat with a Wahler (it was a Motorad before). I am assuming that coolant is coming out of the rad hose when it's hot and spreading. The upper rad hose was already new from a BMW dealer ( a few months old). After replacing the thermostat and refilling with BMW coolant and purging the air the white spray has returned again after driving. Should I return the hose to the dealer? I have not see this before.
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The purge/vent/bleed screws. Coolant drips, the fan sprays it, Please make sure that your tank, housing, hoses are ok. Seeping coolant can become a killer if left alone. It’s good that you are observant. Stay on top of it.
 

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Discussion Starter · #3 ·
I checked my purge/bleed screw and I do not see any leak. The white residue as in the the first photo mostly appears to be at the connection. Very small spray each time I drive. I may see if the BMW dealer would replace the hose for me since I installed it myself. It clicked and feels tight. I don't think , but can not be sure, that the O ring on the hose may have some damage or weakness. I will watch this. Thanks.
 

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If your tstat is Wahler and the Hose is Genuine BMW, there should not be any leak.
As Jim said, look carefully inside the Hose, there is an O-ring, make sure it is not damaged.

Also, during installation, make sure the hose is fully inserted and the metal clip is engaged.

PS: My 1998 528i with M52 engine uses standard hoses and clamps, none of this non-sense O-ring and quick-connect thingy...
 

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Discussion Starter · #6 · (Edited)
I had to follow up on this. I checked over all possibilities for the small coolant leaking out of the upper radiator hose as in pic above and realized I overfilled with anti freeze. Red ball on coolant level way too high. After removing some anti freeze from the reservoir to bring the level to below 'max' I have no leaking coolant spray from the coolant hose. No more white spray.😀
 

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Discussion Starter · #7 ·
I am following up on this suspected coolant leak from last year because it has not gone away. After further inspection I don't think it is my upper rad hose leaking as I concluded above. I still see a white spray as in the photos above showing up after a long drive and the engine gets hot. From the photos above it looked like it was from the upper rad hose. But, I changed the hose for a dealer hose and still saw a white spray showing up on the side of the air intake box as in the photos. It's been over a year and I could not figure out the problem since the thermostat is also new (Borg Warner). Finally I just bought a inspection mirror and was able to look under the upper rad hose and also I inspected the thermostat. I spotted one of the thermostat bolts was wet (see photo below). All the others are dry and so is the connection between the thermostat and the engine. So I suspect the leak is from the bolt. I loosened the bolt and re torqued it to 10 Nm. If it leaks again it looks like I will have to replace the thermostat again because it's probably a hair line crack. I wasn't checking torques when I installed it last year. Good news is there is no overheating, temp guage is in the middle and this is a very very small trickle.

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2001 BMW E39 540i Automatic Sedan, 200 k miles
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It is not the torque of the tstat bolts. It is most likely its gasket that is causing the leak under that wet bolt.
Remove the tstat, replace the gasket, add a thin layer of gasket sealer, let it dry for a few hours, then re torque the bolts.
 

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Wingnut
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how does the t'stat mating surface look on the engine? pitting is known to happen there, lightly polishing/filling the surface may be required to stop the seepage. cn90 iirc did a write up on his leak at the same surface here in the fest, used a different gasket i believe.
 

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Discussion Starter · #10 · (Edited)
(Where do you apply RTV because the gasket sticks out and is in the way?)

Here is a pic of the thermostat removed and the mounting surface when I did the refresh last year.
The bottom left bolt is the problem one right now.
The original appeared clean and smooth to my finger with visible scuff marks.
Just wiped it before installation.
In posts cn90 suggested BMW gasket only and in another to use some RTV.
First I'll see if my re-torque made a difference. Doubtful.
I may not buy a new dealer gasket if the problem is that I just need
to use Permatex RTV sealant.
I'm not used to the idea of adding a sealant but I may just put it on the problem bolt. Thank you!
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Now that I can look back and compare the original thermostat (top one) I can see the same bolt hole
(upper left hole) that is leaking now on the old thermostat. It seems to have wet coolant on it originally. Not something I would have noticed as a new owner except in hindsight with these photos. Looks like
RTV is my next purchase.


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Discussion Starter · #11 · (Edited)
After a second inspection I found that the leak is coming from the thermostat heating element shaft connection. The drops of coolant make a trail and end up on the bolt and makes it look like its the bolt.
There are posts about this on e46 forums with the same thermostat brand I have Borg/Wagner. I will probably be doing a thermostat shaft removal and seal with RTV. Will follow up as I go along. Lucky I bought a mirror.
In the future I will use Mahle/Behr if I have to because their design is a sealed heater rod. It does not come off looks like .Whereas the Borg/Wahler as seen here is an Oring that can leak.
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Thank you!
 

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Discussion Starter · #12 · (Edited)
I tried removing the MAP heater element while it was on the car. There is a tab you have to pry up and it broke.
Then I tried pulling out the element and it cracked. Hard to do on the car.

In follow up I replaced the Borg/Warner with a Mahle/Behr thermostat. The MAP heater is mounted better, permanent, it wouldn't turn or slip out. Less chance of leaking.
I did a coolant re-fill using the dash temp monitor to bring the car up to normal operating temp and burped it twice over two days.
I did not have alligator clips to try to open the thermostat without heating up the car as I was hoping to do. Instead I was running it. It took 40 minutes to reach 97'. The next day after a short drive coolant was leaking from the radiator cap. I forgot to check the level after the car was cold and before I drove it. That's where I thought the leak was from but it
was actually a sheered off bleeder screw close to the expansion tank.
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Discussion Starter · #13 · (Edited)
Forgot to mention I added Reinzoplast to one spot just for added insurance. It's the spot where the coolant was collecting.
However, after I filled and burped the system, the car got too excited and blue coolant squirted out the
bleeder screw which sheered off close to the expansion tank. I took a bus home and got the bleeder screw I had left over from an extra
radiator hose. Bused it back to the car and used a screw driver to remove the old bleeder screw. Problem seemed to be solved.
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I always buy the brass bleed screws from FCP. Just one less thing to worry about.
Same, I am using the same brass bleeder screw I bought from autohausaz from like 15 years ago...I did have to replace the nitrile o-ring on it a couple years ago...found one that fit from an assortment pack I bought from Harbor Freight :) Has lasted through like four expansion tanks so far.
 
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2001 BMW E39 540i Automatic Sedan, 200 k miles
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+1
Use a brass bleeder screw ; check / replace its O-ring ; and most important, never overfill the coolant: With engine cold, the red stick coolant level indicator should NOT extend beyond the neck of the expansion tank.
 

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Always get critical parts like sensors and thermostats from FCP. Brass bleed screw was the first thing I ordered for the old 540i when I started the cooling system overhaul on it years ago. Original plastics ones are such garbage.

So glad the M5 is self bleeding system. Fill it, drive around with heater on til operating temps, shut down, cool off, top off, repeat if needed. Easy as pie lol.
 

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Buy it here:
One and done!
I have one other URO Parts item on my car...their aluminum water pump pulley. (only fits the M62 on the 540)

Both have been on my car for over 200k miles...I'm currently at 336,600 miles today.

Othewise, URO parts are admitedly junk. :)
 
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Discussion Starter · #19 ·
the coolant leakage is back even after replacing the thermostat and the trouble shooting I did above. After I get home from a long drive I look under the hood and see the white residue of the coolant.
It looks like the fan blew it across the air intake box and part of the power steering reservoir. I checked around the thermostat with a mirror and under the upper radiator hose but I can not find the source of any coolant leakage.
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Wingnut
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bring out the holy grenade....oops meant pressure tester. dont overlook possible leaking from the two plastic hoses under the intake manifold, one joins the head on the front driver side of it, looks like its be a very possible source of what youre seeing.
 
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