Got a Motorhome on a Fiat 3.0 diesel 180 multi jet. 2013 model. Heading across France on a 400 mile trip, Keep checking the coolant after 80-100 miles and it's all gone...! Topping back up to max level and the same thing happens another 80 miles down the line. Temp gauge stays fixed at the halfway point. Heaters are blowing red hot.. coolant residue around the pressure cap and all under the bonnet where it's blasted out... We think either faulty cap or an airlock.. trying to find a Fiat commercial dealer in France to get a new cap. Failing that, how do we get rid of an airlock?? Currently feel like we're in limp mode at the start of our holiday! Please help!!

Hi bundle1 must admit I'm. Not up to speed on modern stuff but it sounds like head gasket has gone any mechanic should be able to confirm or not but wouldn't go to far until you get it properly checked. Good luck.

first, is the coolant under pressure?

if you remove the expansion bottle cap (when not too hot) you should be able tell, if there is pressure in system

if there is 'no' pressure the expansion bottle the coolant is just evaporating , just change cap and your good to go!

if there is pressure in system and no sign of coolant spurting out chances are the head gasket is blown and the coolant is going down the exhaust and you have a big problem

Also check for a faulty bleed screw in the system, they usually break if tightened too much then blow out when the system pressurises.

Mine had a tiny radiator leak down on the drivers side totally hidden from view, until they took the grill, headlamp etc, you couldn't tell apart from expansion bottle loosing fluid

I think you have described a text book blown head gasket.
If you start your engine from cold and let it run for a few minutes and you hear 'air bubbles' coming from the coolant bottle, then it is more than likely the gasket.
Don't bother trying any of the sealants available because the pressure is going the wrong way. I won't go into the physics of it, but save your money because you will likely need every penny.
I hope I am totally wrong with the above and please keep us informed.
Good luck.

i dont know if its available in FRANCE but if it is head gasket problem try K.SEAL that should do the trick at least until you get home.