My 855T has a nasty habit of drinking the ethelyne glycol while I'm not looking.
I can find no visible signs of leaks, all the hoses seem good and I recently changed the reservoir cap. Its the green one now.
My first thought is a leak in the head or headgasket. But my mechanic says that isnt likely because there is no condensation on the oil cap.
The leak isnt too bad. I may have to add antifreeze once in 1000 or so miles and only a half quart or so at a time.

Still it is annoying and a bit disconcerting and it will only get worse over time.

Any ideas on what might be causing this will be greatly appreciated

Steve

Condensation would likely show only if a crack was between a cooling passage and an oil passage. But if a crack existed between a cooling passage and the combustion chamber (like with a blown head gasket), you would not see condensation.

As the others said, get it pressure tested.

And if your mechanic didn't mention pressure testing and dismissed the problem because he did not see condensation, then get a new mechanic.

Your mechanic hasn't tryed pressure testing the cooling system? Under pressure, check the heater core, just to the right of the gas pedal (move carpet and plastic piece), radiator (common with older 850s), t-stat gasket, etc.

There was a thread on here a while back that got many laughs. A guy was having the opposite problem as you. His car was making radiator fluid and he was having to syphon some out about every week. He couldn't figure out what was going on, then one day he found out that his wife was mistaking the mark on the resevoir tank and was adding fluid each time he took some out. This was going on for months...with both him and his wife not knowing what was happening. I remarked that as tidy as my wife is, I'm very happy that she doesn't know enough about cars to do any tinkering. It's bad enough that she cleans up my office so that I can't find anything that I need.

Now, on a serious note, I agree that the system needs to be pressure tested. Seems like a gasket leak to me too.
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Current owner of a '04 V70 2.5T. Previous owner of a '94 850 Turbo Wagon