Coolant Leak - Nothing Obvious

[Blakey]

Feb 2005 Carnival, brand new, auto box, 10,500k. It's losing about 750ml over a 3 week period with no obvious leaks inside the car (heater) or in the engine bay. No leaks, no smell, nothing. It's been back to the dealer twice and they can't find anything...last time it was a "air lock". Is there an "additive" that mixes with the coolant and they can see a leak using ultra violet light? or did I see that on Star Wars?

Suggestions please.

[clartsonly]

I would check the levels daily even if you do not use the car. to see if it is after a long journey / hot day etc etc..

[tonyd]

Watch the exhaust - one possability is that coolant is finding its way into the cylinters and is being burnt off that way - possible head gasket problem or cracked cylinder block. If this is the case you may see steam from the exhause although you are probably not losing enough to see much steam.