I wonder if anyone can help. I'm trying without luck to find the cause of a coolant leak on my Fiesta 1.0 ecoboost 2017. I've noticed for weeks that it's been losing coolant slowly and I've topped it up a couple of times. I had the wetbelts and water pump changed very early this year so I've been checking for leaks below that end of the engine and found nothing. I've now found some pink coolant collected in a "pocket" on top of the gearbox casting at the other end of the engine. See attached photo. I've removed the top air hose to take the photo and the arrow points to the puddle. With the engine still warm and stopped for safety I've run my fingers around the pipes and what I suspect is the thermostat housing and can't find anything wet. I've also checked the hoses going back to the firewall which will be for the heater and they are dry too. Has anyone else had this problem and found where it came from ? In my experience, I find if you have a problem with a car then others will likely have seen the very same problem before 😉 . I will borrow a mirror on a stick from work next week and look again but if anyone can point me in the right direction that would be most helpful. The car runs fine and not overheating or anything like that. Thank you in advance. If all else fails I'll book it into Ford as I don't trust anywhere else.

You should add a little light sensitive dye to the coolant and get a battery powered black light to see where the trail goes. T stat housing or possibly a plastic line that serves coolant to or from the turbo could be near that area as well. Just be careful and don’t disturb the plastic lines or fittings. They will become brittle with time and the fittings can crumble just pinching them to remove them from the reservoir. I experienced this with both my Fiesta’s.

Update........... I've now found the leak where the thermostat housing mates against the engine block. Ran the engine until warm and could see a drop of coolant in the mirror. Have ordered a complete new thermostat housing with gasket, thermostat and temperature sensor direct from Ford online shop. I notice they have sold lots of them !