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Wingnut
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look at the weep hole on the bottom side of the water pump
 

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Discussion Starter #26
My latest hypothesis on the coolant leak...

After driving the car for a few minutes and parking it, I put my head near the kidney grills. I can smell coolant.

If I can smell coolant that far forwards of the car, the leak has to be at the radiator and probably at the bottom of the radiator (because I can't see it dripping and the bottom of the radiator is not visible. Its got plastic covers on the bottom).

Someone please prove me wrong (other than my wife)!
 

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Wingnut
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ive no way to prove you right or wrong online, but one can rent or borrow a pressure tester from most major parts places. pressure testing the system will help you isolate the leak without having it get blown around from its source
 

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The crank pulley looks dry. That could be from road spray. Take a very close look at the water pump and thermostat. Our N52 pump hasn't leaked but I've replaced 3 pumps on our N54. I know they are different but... ... Also, the pipe that runs from the head to the water pump has a plastic firring on the head end. They crumble. Yours could be leaking a little. Ours blew off in traffic and dumped the coolant instantly. You don't want that.
 
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I wouldn't let the "sniff test" alter your opinion too much - you'll be able to smell leaking coolant anywhere the inherent airflow through the engine compartment goes, and (if the fans aren't running), that would up up and out the grille (as the obvious exit point for rising air from the hot engine block).
 

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Discussion Starter #30
Yes, the crank pulley has always been dry, but the white marks and rust marks are a bit worrying.

I'm leaning towards buying a new radiator since the radiator is over 10 years old.

My guess right now is the bottom of the radiator might be cracked and leaking and that's why I can't see a leak (or produce one when I pressure test it).

Last year I replaced the:

  • upper radiator hose
  • lower radiator hose
  • mickey mouse hose

If I pull the radiator and install a new one you think I should replace the hose from the expansion tank that runs all along the bottom of the radiator and connects to the heater control valve hoses on the other side?
 

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In regards to your sludge question - if there where sludge under the oil cap it would mean that coolant is being mixed with the oil, so typically a gasket failure..
Hope that answers it.
 

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2007 530i
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I was chasing a coolant leak on my N52 for a while. Eventually I got an o-ring kit off eBay ($20) and replaced all the o-rings inside the plastic clip on hose ends. It was either that or replace the hoses ($$$!) Since putting new o-rings on it's not lost a drop. Also, might be a good idea to replace the "mickey mouse" shaped hose connector on the front of the block under the oil filter housing (it's black plastic and has two small bolts holding it to the block). That connector is not spared by BMW and has a crimp on metal band, but you can cut the band off and replace just the plastic part with an aluminum replacement which is cheap and readily available from aftermarket companies. If you wait long enough, the plastic becomes brittle and fails catastrophically when you least expect.
 

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I was recently leaking in that area. the thermostat had some crud built up, causing a small leak. I took it apart, cleaned up the o-ring slot, and put a new o-ring in. seems to be gone. very weird leak. o-ring was fine, just had a tiny amount of crud built up. not enough that you would think it would cause a leak, but it sure seems to have. I could see coolant leaking down on to the belt after sitting over night. btw- found it very easy to confuse coolant with the green p/s fluid chf-11

 

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Discussion Starter #34
I replaced my thermostat and water pump last year. They appear to be clean from coolant (but they are on the other side of the engine where the coolant leak is located)

There are a few drips of coolant on the power steering high pressure hose fitting (where it connects to the power steering pump). The only component above that was the air box. I took the airbox out and everything in that area looked dry except for the power steering fitting.

I pressure tested the expansion tank to 10 PSI and no leaks were found. I think I'm going to have to pressure test it to 15 PSI and see what happens (without breaking something that wasn't broken before I started).
 

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Scott,
Know this probably doesn’t help you but on my 545 have had a slow coolant leak for over 1 year now and have not been able to find the source despite pressure test and searching for it many times. If I recall correctly it started some time after replacement of pump and thermostat hoses etc. some two years ago. Best I have been able to do is determine it starts somewhere in the middle front of the engine' and top her up.........
 

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Discussion Starter #37
Update:

Today I pressure tested the car again and put 18 psi into the system.

It held 18 psi for 15 minutes straight and didn't loose any pressure.

During that time I looked high and low and didn't see any coolant dripping, but the bottom black belly pan that covers the underside of the car is soaked with coolant ( I cleaned it yesterday). I can confirm its coolant on the belly pan because of all the white residue the coolant leaves behind.

I took another picture of where I'm finding coolant.

1024437
 

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Discussion Starter #38
I'm at the point where I may just have to resort to topping the coolant up every 2 months, and buying a new belly pan cover.
 

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Nuclear engineer
02/2012 X5 35d M57Y CPO 100K miles NOKIAN WR G3 20K miles
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How precisely are you adding makeup coolant and at what rate?

My very different car has two flats in the expansion tank labeled MIN and 25 mm higher MAX. I keep the MIN flat just wet by adding maybe 10 ml every month or so, maybe two months. I have a mechanical WP and expect weepage.

My point is, topping up coolant every two months could be inconsequential.
 

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Discussion Starter #40
I put about 4 ounces of coolant in the expansion tank every 2 months. I usually put the car up on Rhino ramps every month and remove the black engine cover and inspect and look around for leaks with a trouble light.

This car is a hobby of perpetual fixes (proactive and reactive). I wish the coolant leak was much worse so I could just replace the part.

My latest hypothesis was the radiator was cracked, but I'm dismissing it now because I can't validate it.
 
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