[ASt85]

Originally Posted by john d

My guess is that there was some degree of differential thermal expansion (or contraction) due to the mix of metal and plastic radiator components. The gap tightened up as the components heated up, and stayed water tight when up to temperature. When cooling down, the components on one side of the gap cooled faster than those on the other side, widening the gap enough to leak. Only my speculation, mind.

Good advice - it is also as well to check for moisture under the passenger side rubber foot mat - if it is damp to the touch and feels quite slippery then you may find you've got a minor leak from the heater matrix connection - the "O" ring seals are prone to leak after the car has done over 150K probably for the same reasons outline by John D above.

The leak begins very, very slowly when cold - the hose connects to the matrix on the left hand side as you look at it from the seat - I couldn't find a leak until having checked several days in a row finally found a drop of green Volvo antifreeze just about to fall from the joint. Subsequent removal of the under-facia revealed a greeny/blue blob of crystalised anti-freeze where the drops had been falling before they found there way to the carpet. As above there was no leak when the engine was running or was still warm.