Isn't the coolant system a closed loop?

[uflnuceng]

Ok... my wife may have a radiator problem, although she has been pissing me off lately and nothing would make me happier than a big fat I told you so when her car over heats on the side of the road...

Anyway, her coolant level is dropping in her 2003 330Ci... but I see no leaks. I'm under the assumption that the radiator system is a closed system, i.e. its not suppose to boil or leak out under any means... except if the pressure relief valve goes and I don't know if BMWs have that.

I noticed that her level was a little low about a year after she got her car, but it was the first time I checked so I topped it up with distilled water and called it a day. Yesterday her coolant level light went on and I told her drive right home... amazingly enough she actually listened to me this time. I let the car cool for a few hours and then opened the radiator cap... HOLY CRAP was that thing low. I had to use about half a gallon of 50/50 distilled bmw anti-freeze to fill it back up to the appropriate level.

The newer BMWs have those damn plastic undercovers so I can't see anything leaking, and her catalytic converter is new enough that if there was a small block leak I'd never see it... is there a safe reason why her car would be loosing coolant? Can it be something not as tragic as a block or gasket leak? Stealerships are so damn useless now-a-days with stuff like this that I wouldn't trust them to troubleshooot it... this car would have to be smoking for them to have a chance to find the problem.

Anyway... everyone's $0.02 is greatly appreciated.

Jared

[E30godz]

check oil dipstick for milky residue.

take to BMW under warranty and say FIX IT

[uflnuceng]

check oil dipstick for milky residue.

take to BMW under warranty and say FIX IT

milky residue in oil... i knew there was a check.

I'll still talk to the BMW people even if that comes up fine.

[AdamF 88iS]

Common leaks on that car are thermostat housing and radiator/expansion tank. The clip on hoses can let go sometimes too. Make sure you open the bleed screw when you're filling it.

[uflnuceng]

Common leaks on that car are thermostat housing and radiator/expansion tank. The clip on hoses can let go sometimes too. Make sure you open the bleed screw when you're filling it.

Good call... pain in the ass part is all the freaking plastic in the way:(

Whatever happened to having a beautiful looking engine? Now-a-days you take the plastic off and you got one fugly looking piece of metal... at least the old ones, S38, M20, M30, S14, even the 4-cylinders look nice just as they are. Guess the plastic goes with covering up more electronic complexity.

[JeffG]

I know many of you don't like the dealerships, but the people there do know what they are doing, they are not stupid. No offense, but they'll know a lot more than you do about this thing. This car is (should be) under warranty. Drop it off at let them fix it for free. We get dicked on warranty time so take advantage of the free work and getting to stick it to someone while you do since it's not customer pay.

Expansion tanks sometimes crack, not often, but they do. It's very easy to remove that under body covering, a screw driver is what you need, half twist the screws out and pop out the three black little plastic rivets across the front and it's off. Check underneath the expansion tank for any signs of leakage, residue, ect. Pressure testing the system when full is the best way to find leaks. Also check your cap, see if that thing holds pressure or not, you'll see coolant disappear quickly if it doesn't hold pressure.

Another good spot, as mentioner earlier, is the thermostat housing. Those will leak and cause coolant loss. BMW cooling systems can be very tempermental on later models so be careful while working or taking things apart if you will do this yourself. Also as mentioned earlier, open up all the bleed screws when filling. When bleeding the system, turn the heat on full hot so the water valves open completely and are not pulsed so all the air can get out of the heating system.

I'm a dealer tech and have done a lot of cooling system work on M54's in the E46's, those are the three things that I see the most. It is normal for coolant loss, all of them do that, but you shouldn't have to fill it with a half gallon or more obviously. Any questions, please feel free to drop me a line, I'd be glad to help.

-Jeff