I did some quick weekly checks on my 2008 Fiesta Mk6.5 earlier (oil level, coolant level, etc.) and noticed that the coolant level was on the midway point but I'm certain it was higher a few weeks ago. I slightly suspect a coolant leak but I'm not certain - I'll top up the fluid and see how it goes. I'll check the expansion cap and pipes that I can see but are there any other checks I can carry out? The timing belt is due in June 2018 but would the water pump be leaking as it's coming up to 10-years old?

Leave it for a while and check to see if there's a puddle on the floor. Also make sure your doesn't start overheating, the last thing you want is the cylinder head gasket to have blown and the coolant to mix with the oil.

Check through the oil filler cap for any signs of a milky substance. The only thing you want in there is oil and the precisionly machined components that make up the head.

Goes without saying make sure you top up with anti-freeze rather than water too at this time of year. 

Midway point is where it should be when cold.  It'll just blow any excess out of the cap when it heats up if you over fill it a bit.  Keep an eye on it but I'd say it's probably not a problem.

Maybe change the water pump at the same time as the belt, that’s what I did.

Levels will change a little with temperature.  

When it's baltic like the last few days, wouldn't surprise me to see the level lower by a little. 

Thanks for the replies. It's freezing where I am at the moment so that might explain it. I didn't know that the level would drop when it's cold - you learn something new every day. I'll keep an eye on it.

take your car out for a run so your temperature is normal then let it stand idling and make sure the fan is kicking in, if not and it starts boiling over get it to a garage asap, could be your temperature sensor or a fault with your ECU

check your engine core plugs (the well where your spark plugs are) for fluid, could be worn core plugs leaking

could be a split pipe, worn thermostat housing, if it goes down very slowly its not something i would worry about, i need to top my coolant up every so often due to a small leak from my top radiator pipe, i could get it fixed but its nothing major and my car is an old man so want to limit any unessential bills. hope this helps