as i was checking on the engine oil and noticed that the coolant expansion tank was empty!!! hurriedly topped it up and went out for a 10 minute ride. after a couple of hours i checked on the expansion tank again. to my surprise it was empty!! 2 hours with only 10 minutes of driving and it was empty! filled it till MIN level this time. i revved the engine on a steady 2.5 krpm for a minute for every 3 minutes. each time monitoring the coolant level and looking under the car. after 30 minutes passed, it seemed to stay on the MIN level. then left it for another 2 hours. I came back to see the expansion tank empty again.. oh, i couldn't see and feel any leaks on the expansion tank, plus i was constantly looking under the car for any fluid drops. so far nothing..

any idea? i've read about the thermostat and the housing being mostly faulty, but i'm not certain that it can drain the fluid at this rate.. i haven't encountered overheating so far as it is winter...

i have an r50 '02..

thanks!

 

What does your oil look like?
I had a mysterious coolant leak, even after I replaced the expansion tank.
Found out it when I replaced my supercharger that it was weeping out around the o-ring (from the pump to the block). I never saw any drips or anything, and my oil was clean. It just seemed to be vanishing, much like yours.

 

weird thing about it is that the coolant is drained while the car is not running.. shouldn't all fluids settle when the car is not running??

my oil looks like it's due for a change, but it still is clear. not sure how they refer to the creamy feature when coolant and oil mixes.. but yes, i'm very certain the oil is not contaminated.

would you be able to point out as to where this o-ring is (from realoem diagrams)? also, are you refering to the water pump? my apologies, i'm not familiar with where most components are.

were you able to replace it yourself? if yes, how long did it take you and how difficult is it?

thanks!

 

Are your floor mats wet? (possible heater core leak.)
Does your car smell like burning antifreeze? (Leak on block an evaporating off.)

 

floor mats are dry and i don't smell any burning coolant.
i'm noticing sloshing fluid near the dash. i've read that it may be a sign of a leaky pump/o-ring or air pockets..

i might as well replace the o-ring, t-stat, and housing just to be safe...

i've seen some diy replacement instructions for the t-stat and housing, but couldn't find any for the o-ring. anyone has one for the pump o-ring of an r50?

thanks!

 

I had something similar to this happen to me, however I did have a puddle forming underneath my MINI after sitting a few hours. I even had the sloshing water sound behind the dash. Took it in and was told my thermostat housing was leaking. Had it replaced, and supposedly the coolant system was flushed, but I still had the sloshing sound behind the dash. I had to bleed the coolant system myself to cure the air pockets. I had to fill my resorvoir to the max several times and now it ultimately rests just above the minimum line.

I would definitely do the checks you stated, and just keep a close eye on the level.

 

http://www.realoem.com/bmw/showparts...99&hg=11&fg=35

For some reason the pic wont show. I believe the o-ring (number 7 on the diagram), would be the same as the o-ring on the r53. It goes from the water pump into the block. This is where I was loosing coolant. However I never noticed a drip under the car, nor did it leak when not running...it just vanished. Hope you find the problem. Let us know what it was when you do!
Good luck.