Hi , I replaced  the expansion tank on my ford focus 1.6tdi 2008 as the thread where you put the cap on was damaged, so after  replacing the tank i then filled it back up with new  coolant , so far so good. I then took for a drive for  a couple of miles and checked the the coolant level and the coolant and mysteriously disappeared , I opened the cap and the coolant came flooding  back into the expansion tank but everytime I drive the car now the coolant disappears.  Please don't tell me its the head gasket, I'm hoping it's a quick fix any advice 

Regards Fraser 

If the coolant isn't burning off and comes back into the tank when you switch the engine off, then it cannot really be a headgasket failure.

I'm guessing you now have an air lock you need to bleed.

Bleed all the coolant out and put new coolant in , is that what you mean ? 

With the engine cold, take the top off the expansion tank and fill it to the "Max" line. Leave the cap off the tank and start the engine, let it reach normal operating temprature and idle for a few more minuites.

Switch off and let things cool down and refill tank back to the Max line and replace the cap.

It can take a few days for all air to work itself out of the system, just keep an eye on the coolant level. Don't overfil it and only top it back up to the Max line when cold.

I'll try that , thanks for your reply 👍👍