My 140,000 mile, 1995 Mondeo 1.6 Zetec is poorly. For a while it's been losing coolant. The a few weeks ago I checked the oil on the Saturday and it was fine (a bit low so topped it up) but on the Wednesday I noticed the sump had a load of water in it.

I've taken the head off and can't see signs of distortion or cracks on it, but there is a mark on number 4 cylinder liner, but it doesn't look or feel like a crack when you run a finger nail or sharp point over it. Also the valves and piston on that cylinder were cleaner than the others, suggesting steam had been getting into that bore. I've tried marking over the black mark with a marker pen and pressed hard to force ink into any crack, but when you wipe it off there's no line left where you'd expect a crack mark to be left (if that makes sense).

Anyway attached is a link to a .pdf of some photos and comments that I emailed to a mate of mine for a second opinion. We both felt that it was the head gasket and nothing more, but having now spent a bit of time rebuilding the head and cash on new exhaust valves, timing belt etc., I've revisited this curious black mark.

What say the Ford experts here? Should I press on with the rebuild or should I cut my losses, stick the new parts back on ebay and scrap the car. Do we think the black mark is a result of coolant leaking through the head gasket and staining the bore or is it something more sinister?

Any thoughts or advice most gratefully received.

(Hope the link works. I gather you'll need to enter the code at the bottom and wait 25 seconds before clicking 'download' at the bottom of the screen):

Head_Report.pdf - 2.7 Mb