Hello, My sister has a mk 6 2006 Fiesta 1.25 Petrol with only 35,000 miles. She has been recently been experiencing intermittent coolant loss, and the RAC, and her local garage has been unable to identify the cause or make it happen. The first time steam was coming out and she called the RAC, who identified loss of coolant, but could not find a leak, so topped it up and it was fine. Maybe the reservoir cap had got loose or something. Two times now she has noticed coolant on her drive and the reservoir was empty, but in between those times she has driven it loads, up to the lakes etc and it has been fine. One time the temp gauge got to the red so she stopped. The garage has checked the fan was working, have pressure tested it, and checked for leaks, left it running for ages, and just can't find anything wrong! It's a total mystery! But she's nervous of driving it as it will probably do again: she carries water with her. Has anyone experienced this before or have any ideas please. It's really frustrating! Many thanks, Simon

95 views, and no reply, so I can only presume that no-ones had this before, it's not a common Fiesta problem, and no-ones got a Scooby Doo what the problem might be! 🤣

Definitely not a common problem that's for sure, at least you can tell it's an external leak so it rules the engine out. 

Only thing that springs to mind is the coolant pipe connections in the bulk head (under the scuttle panel) that link up to the heater matrix, this wouldn't necessarily be visible as the coolant runs down the insulation on the bulk head. 

Other than that a possible sticking thermostat causing the car to overheat and boil the coolant in the reservoir which then forces it's way past the coolant cap.

Put some leak detection dye in the header tank.  It'll show where it's leaking.

We've used this at work to find a leak before: https://www.ringautomotive.com/en/product/RLD2

what about leaking water pump or as said the thermostat sticking...would the thermostat sticking show up if i was scanned?

Apparently it's had a recent new water pump, and thermostat. But in any case that surely wouldn't explain why it only sometimes happens, and why the garage can't find anything wrong when it's not leaking!

4 hours ago, jaguarsimon said:

Apparently it's had a recent new water pump, and thermostat. But in any case that surely wouldn't explain why it only sometimes happens, and why the garage can't find anything wrong when it's not leaking!

i was going to ask if it had a new water pump done...i had a water pump and timing belt done on my zetec s 1.6 few months ago and the coolant was fine when i got it back but after driving it, it needed topped up so i topped it up and then drove it a bit and needed topped up and then did it again like 3 times...and now its fine. i spoke to another garage at the time not the ford dealer who did it and he said it was a possible air lock or something in it....but... there wasnt any coolant leaking out on the floor though and the level hasnt gone since i filled it up like 3 times.

could be the radiator leaking from a small crack guys?

It doesn't appear to be a constant leak. It was left for a few days, and the level had gone down a few cms, with some on the ground, but then driven for a further few days with no leak at all. This is why it's such a mystery!!!

46 minutes ago, jaguarsimon said:

It doesn't appear to be a constant leak. It was left for a few days, and the level had gone down a few cms, with some on the ground, but then driven for a further few days with no leak at all. This is why it's such a mystery!!!

yep it sounds like a mystery... when i had my water pump/timing belt done i didnt see any that had leaked out on the ground and topped it up with proper coolant not just water but did it like 3 times as i said.

Looks like the only way forward is to use the coolant leak dye which someone has suggested. My sister has ordered the dye and UV torch. Fingers crossed this can locate the problem!