Hi I have a 55 reg Ford Fiesta 1.4 16v petrol and this morning checked the coolant level and all was good but after driving for about 20mins to get some petrol went to fill the wiper reservoir I noticed there was no water in the coolant tank but when I started to loosen the cap the coolant level came back up

any advise would be much appreciated 

What level did the coolant return to? The coolant level MAX line is difficult to see, especially if you're tall as its above the wording, make sure you've got enough coolant in the system and not mistaking the line below the wording which is the minimum mark.

Hi

it returned to max level

 

There's an air bubble in the system.  Just needs bleeding.

On 2/11/2022 at 8:48 AM, Odd-job said:

Hi I have a 55 reg Ford Fiesta 1.4 16v petrol and this morning checked the coolant level and all was good but after driving for about 20mins to get some petrol went to fill the wiper reservoir I noticed there was no water in the coolant tank but when I started to loosen the cap the coolant level came back up

any advise would be much appreciated 

As Tom states, very likely just an air lock (which can be  a pain to get rid of at times). The actual plastic reservoir are known to leak also, from the join at the bottom, so any older Fiesta I buy (I have bought a few for family members), as a matter of course, I always change the fluid reservoir as a precaution. Pattern parts are about £15, Ford item about £30, easy job.