Hi guys, having a bit of a problem with my fabia. About 6 weeks ago my coolant light started coming on when I first started up the car. Coolant was getting low, topped it up, ran fine for a few days, it's started doing it more or less every time I start it up now, hot or cold, coolant is very slowly dropping but it does it when it's full aswell as low, engine temp is fine. There is mayo under the cap but I'm told that generally happens when it goes on short runs a lot. Only other thing is apparently It's sticky to the touch inside the header tank. I do have a replacement as it seems there's something wrong with the sensor anyway, but I haven't fitted it yet As I want to solve whatever else is wrong first.

Hello Rusty, and welcome to the site. You are posting in the wrong section, this is the Fabia Mk2 section. But I can say that clearly you must have a leak. Sticky inside the header tank, that's pretty normal. Mayo is as you indicate pretty normal too on short runs. It's unlikely to be the head gasket leaking but it's still a possibility. Is coolant getting into the oil? That would increase the amount of Mayo present on the oil cap. It's more likely you have a weep or leak from a hose somewhere. Your car is now 13 years old and any hoses that haven't been replaced will be on or at their limit for integrity of the coolant. Often what happens is they leak under pressure and this can often only be evident when the engine is running and being driven. Look under the bonnet for traces of coolant on the bulkhead and lower end of the motor. Check the radiator tubes for leaks with the motor hot and cold. It may also be the system is not pressurising properly due to a worn out head tank seal or cap. Good luck with this and post back with any finding you see. 

Oil is clean as far as I can tell, thanks for your help, I'll let you know how I get on.

I think I have found the leak. Tied some tissue round the joints in the pipes and ran for a week, took off yesterday and one of the joints under the engine had made a slightly orange stain on the tissue, that looks like an oil stain (almost like from a curry) so we're going to look into changing the pipes and the header tank at the same time.