Coolant loss but no visible leakage

[jimjay001]

Hi All, new to the board here.

My 2003 Z4 has been burning through coolant quickly. About a month ago, my coolant level light came on and I topped it off. About 10 days later, it was on again. Topped it off and the light came on once more yesterday. There is no visible leak that I can see and no puddle underneath at home or at the office. Could something else be causing it to burn through the coolant so quickly?

I've got about 65K on it and keep it up to date for service.

Thanks!

[wildag]

I had the same problem in my 2001 Z3 3.0i. The problem ended up being a warped radiator overflow tank. The cap wasn't screwing all the way down to a sealed position. So when the car was very hot, the coolant was steaming out from under the lid. The only sign was a little bit of dried coolant residue around the lid.

Replaced the overflow tank and the cap to fix.

[The HACK]

There could be hundreds of possibilities here. Inspect the entire cooling system for signs of leak. Leaking coolant will leave a white chalky residue. I know you said there's no visible signs of leak, but it can leak from some very unlikely places...

1. Waterpump. Inspect the pump for any signs of white chalky residue.
2. Warped head. Inspect OIL for any signs of white milky residue.
3. Thermostat housing. Inspect for any signs of white chalky residue
4. Radiator nipples. Inspect the radiator's connection to the various rubber hoses and expansion tanks for any signs of white, chalky residue
5. Expansion tank. Look for white chalky residue.
6. Bleeder valve. I believe it's a small valve with a cross on top on the neck of the expansion tank. If this valve is cracked it will allow heated up coolant to escape in form of vapor. If there's a leak here, there should be some signs of white, chalky residue.
7. Check the engine block on the passenger side, on the 3rd cylinder from the front. There's a coolant drainage plug. Check for white, chalky residue.

Check everywhere and anywhere for white, chalky residue for signs that the coolant may be leaking slow enough for it to vaporize and leave some residue without leaving a puddle.

[jimjay001]

Thanks a million for the advice. I'll check it out!

[car62]

Immediately after driving the car open the hood and crawl around all over and inside the engine compartment looking and smelling for a leak. Anti freeze has a distinct odor that is unmistakable. At least the traditional antifreeze does. I don't know if the BMW product smells the same, or differently. Definitely check the oil for signs of coolant in the oil, which could be caused by a bad head gasket or cracked head. Eventually the leak will rear its' ugly head, you just don't want it to happen at an inconvenient time or place. BMW radiators tend to leak at the junction between the aluminum and the plastic side tanks, look carefully there also. There is a kind of dye that the shop can put into the coolant which shows up under a special light, you may have to resort to that method.

[buddrinker]

If your head gasket is gone..you may not always get antifreeze in your oil. It will just send it out your tailpipe. Get your car up to operating temerature and have someone rev the engine to about 3000rpm. Hold your hand over the exaust and then smell your hand. If it smells like antifreeze then you know its a head gasket. Also look for white steam.

[scottyD]

The reservoir cap has a safety valve to prevent a large buildup of pressure in the cooling system, and you could have some small coolant loss through that over time.

I had similar coolant loss issues, and honestly I think it was improved by just twisting the cap on tighter than I normally had been doing.

[steve99m3]

If there are no visible signs in the engine compartment, I'd suspect a bad head gasket.

[1gshow]

Did you ever find a solution? I am having the same issue. Keeps losing coolant with no visible leak. Just changed the oil and the plugs. No signs of coolant in the cylinders or oil. So i'm thinking expansion tank??

[Shipkiller]

I had the same issue on my 03. I was filling the reservoir up every 10 days. I could not find any leaks, but I did notice that the aluminum parts of the engine were starting to show signs of corrosion.

I finally tracked the problem down to a bad O-Ring in my lower radiator hose allowing coolant to leak under pressure and flash to steam when driving.
Replace the hose, and that fixed the issue.

Not saying that this is the issue but one more area to look at. 'The Hack' has a nice list to look at...