Coolant leak
 

It seems there is a coolant leak from the expansion tank. I'm not sure where exactly though. If I top it off, the tank will be empty in 2 - 3 days, but I don't see traces of a massive leak. The hoses look OK to me, so I'm thinking a crack in the tank that leaks under pressure.
Has anyone dealt with a similar problem? Should I replace #3 in the diagram as well? http://www.realoem.com/bmw/showparts...41&hg=17&fg=05

if you have not done a cooling overhaul, consider the leak as a warning and do it now. Tstat, WP, Hoses, Tank all that.

+1

When I got my car I had those issues it was due to the radiator nd fan clutch being changed and not also replacing the expansion tank.... U may wanna look at your expansion tank and its portholes. Hope you don't have a major headache pending. Good Luck

you may also want to check the side of your radiator that faces your expansion tank. I had the same symptoms, and my problem was a hairline crack in my radiator. It only leaked under pressure

Due to the many common problems with the cooling systems on these cars you should give it a real close inspection. Yes you see leaks in the expansion tank as well as radiators and waterpumps. If you have a way I would pressure check the system to pinpiont what is leaking.

I replaced the pump & tstat about ... well, I guess about 50 000 miles ago. The hoses look good. Maybe I'll try adding some of that glow liquid to the coolant. I sure hope it's not the radiator.

2 year old Behr ...
http://www.youtube.com/watch?feature...&v=S2eqA7vzmww
See also:
- Pictorial look at typical E39 cooling system failure modes (1)

Radiator is cheap and easy. Well, except for that darn auto trans fan deal.

The original Behr radiator is around $300 and might not be the problem. I've seen cooling overhaul kits including an aftermarket radiator for about the same price, but I don't really want to replace stuff that does not replacing. I'm considering replacing the pump again as it's a well known failure point, but my upper radiator hoses are nice and soft, the t-stat is new, the lower hoses look OK ... Just need to find the damn leak :confused:

Removing the fan is not a problem. I've done it a few times and i can now take it off in 10 minutes flat, along with all air intake crap.

Any tips for me on speeding the process of fan removal? ;)

Also check the aux temp switch sensor on the lower radiator hose. That can be a slow leaker that shuts up when cold. That was actually the first to leak on my car, around 80k miles. The expansion tank started leaking about 10k miles after that for me.

Good luck!

Do it 10 times, on the 11th time you'll be a pro :rofl:
What I do is to whack the wrench with a hammer. That's about enough to "break" the nut. If that does not work, use a long screwdriver to prevent the belt from slipping.

Very funny! :cry: but that makes sense given what others are saying too. I'd prefer not to have to take the fan off 11 times ;)

This ^^^^^^^^You should be able to see, even the tiniest leak under pressure.

If not, check for coolant from the exhaust pipe. Then maybe if not this, what does your oil looks like? Chances are the leak may be internal.

I found it. I poped the hood and looked carefully - I noticed white spots on splash shield on the driver side. The passenger side was dry, so I took off the air ducks and the filter box. I didn't notice anything at first, but then I noticed it. It's right behind where the two houses connect to the tank. There was a bit of coolant right on top of where the hose is connecting to the tank. Very sneaky and hard to see. I guess the tank is leaking a bit under pressure.

Where does your regulation level wiring harness goes to. Sounds as an electrical problem. I'm guessing some of your coolant in your coolant reservoir goes somewhere around your engine your car system it's a bit complex. Since the level wiring harness it s spliced somewhere. I don't know if your're aware about your coolant lines going directly to the automatic transmission.

It's not electrical. I check the float in the expansion tank and it's completely dry. I also noticed coolant on the side of the tank, where the hose plugs in.

Which tank is the one you're mentioning.

Expansion tank leak
 

I had a small puddle everyday after work right under the expansion tank so I bought a new tank from ECS Tuning for around $50 and part #3 in the diagram. When my mechanic got in there though it was actually the mounting plate #1 where the tank sets in was cracked so I needed to get #1 for $185 or so from the BMW dealer due to time constraints.
All is well now. :)