I'm in the process of renewing my coolant but I can't see the level in the header tank.if I dip a stick in how far up should it register for full and low

The water is being lost out the expansion cap, we hear it spit it out when driving

Don't know of bongo friendly garages in Northern Ireland. My husband works on all our vehicles so will have a look at bleeding the system( as shown on the video) and see if that solves the problem

The fans running constantly was set up to prevent over heating, something which we have used on other older vehicles that have a tendency to over heat. There are no rust stains in the water bottle, no obvious leaks anywhere, only the spitting out of water. The system is a pressurised one

It is a 2.5 td that has had no work done on the pipes. We have to top it up every time we take it out because of this. Engine runs fine with no smoke or overheating, although the fans are wired to a switch to run continuously to help keep it cool

After driving for a while the expansion tank can be heard spitting out water, yesterday four times during a 80 mile trip. Is this a faulty cap, airlock or something worse.