Gradual coolant loss on Z4 and other BMW engines

E

eurgain

Member
 North-East Wales
Hi, All

I have a late 2003 3.0 Z4. my partner has a 2002 E46 325ti Compact, and my mother has an early 2003 E46 330i Touring. All of these cars have similar engines and a similar strange tendency - they "use" coolant.

What I mean is, if you use the floating dipstick to set the coolant level correctly, all of these cars will loose some coolant as time passes. My mother's car has actually lit up some light to warn her to add some more coolant inbetween services. My car certainly looses about 500ml a year (much more than the oil it uses!), as does our 325. I am not meaning that I overfill the coolant and it dumps some - I mean that the engines gradually "use" it over quite a long period.

Do others find this is so?

My experience with all other cars is that they mainly loose no coolant at all, or have a leak and loose the lot, but not just having it go away slowly. I have never encountered this situation before where a car looses a little over time. Where is the stuff going?

A
 
Losing 500ml a year is not that bad. Make sure the radiator cap is in good condition and closed tightly.
 
500ml a year is nothing!! My 328i lost that in a month!! If that's all you're losing it's nothing to worry about, perfectly normal, it may be a 'sealed' system but its not really, it has a breather to lose pressure if it gets too high and rubber hoses never fit perfectly, all engines will use coolant to some degree.
 
On my 03, I had the same problem.

BMW uses an O-ring on both ends of each radiator hose. Over time they can wear out. While it is hard to find the proper size O-rings, I just replaced one of my hoses.

If you look at the post below, in one of the pictures you can see the O-ring inside the hose....

http://www.z4-forum.com/forum/viewtopic.php?f=12&t=9385

The other wear related component of the coolant system is the 'Expansion Tank" They can go bad, or have the O-rings go out....
 
Mine also looses coolant, more than i would like in fact.
Which reminds me that i need to top that up, last time i checked the dipstick was lower than it should...
 
And don't forget, even with the smaller engines, that bay is FULL. It's hot under there and easy to evaporate off coolant.
 
In a modern engine, there should be NO loss of coolant. None, Nota.

If the system is functioning properly, with no leaks, it just can't evaporate off..... sorry wrong answer.... ending bell....

If you do not have an external system leak as I talked about above, then there is a leak internally to the engine. Normally those are big and noticeable.......in many ways...


The system operates UNDER PRESSURE. That's how it keeps the glycol/water mix from BOILING and becoming steam. Most likely you have an external system leak somewhere. It does not have to be big and noticeable.

I never actually saw the leak. I only way I found it, without just throwing parts at the problem, was I noticed accelerated aluminum corrosion on certain parts and not on others. That was like an arrow to the source...
 
OK, perhaps I stated it wrong--loss of coolant from places like the overflow tank and other vented areas.
 
The cap has a safety valve on it that opens up when the pressure inside the system rises to a certain level. For those of us who have to top up the coolant on a regular basis, it is probably due to the valve opening once pressure is built up, which releases some moisture from the system. Over time it adds up. Mine has done this since brand new. You can even see some of residue from the coolant that had escaped and dried near the filler cap.

Lately though I have noticed the loss rate decrease if I make sure the expansion tank cap is pretty tight...


I lost coolant on my older car, a 1992 Volvo. The engine block had some porosity issues, and pressure from the cylinder was escaping through the cylinder wall and into the water jacket, and bumping up the pressure on the system overall. After a few miles, coolant would be spewing from the cap due to the safety valve. This was very obvious and a much greater leak rate than what we are experiencing with our Zs.
 
The reason for you gradual coolant loss is the thermostat, or better to say thermostat housing. That housing is plastic, and is well known for letting the water out albeit slowly. The thermostat and housing should thus be changed by your Bmw service at around 50k miles. My 2003. 3.0 had the same issue, and after the thermostat and housing (they come as one) were changed it never happened again.
 
So glad I found this thread. Was a little concerned after my last hooning session when the coolant light came on :o


Sent from my iPhone using Tapatalk
 
I haven't had to add any coolant to mine in nearly 4 years including a trip to the 'ring.I'm going to check it tomorrow though just in case :D
 
My 2003 3.0 was losing small amounts of coolant over time, similar to your description. I took it to a dealer and they replaced one of the coolant hoses under warranty. Since then the level seems fine, touch wood!
 
Sheez... know what my first job will be tomorrow. No car I've owned since about 1989 has ever had an issue with coolant loss, no matter how much it has been ragged... better see what's left if this is a common 'feature' to many on here.
 
I have been searching and came across this thread. We looked under my bonnet and noticed the coolant level indicator was on *alarming low.

Quick phonecall to the Indy garage to ask what coolant I should use, blue or pink?and whether this was topped up at the last service? - he told me my 2004 car should have lifetime coolant. What? That can't exist? Lifelong? (The boys at home were laughing at me by this point). Surely something loses it's effectiveness.

Was I being fobbed off? Why didn't the garage check the level? My last service was about 14 months ago.

N.b. the liquid in the coolant chamber was... clear - WTF. :o

And oh, no warning light incase anyone wonders.

I welcome any help / advice purlease.
 
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