Is220d coolent leak

[Amer]

Hi guys I’m new here sorry if I make any mistakes.

I have a 2008 is220d sport 97k Miles which I recently purchased,the car drives spot on but last couple of weeks I have noticed coolent spray on the engine (white chalky residue)I gave it in to my local mechanic and he checked the car over and told me the coolent spray is coming from the expansion tank out of the overflow pipe and there is smoke for a few mins then stops.

i noticed the expansion tank only has plain water and not antifreeze and there is some coolent loss,I top up about a litre every few days.

is this the dreaded head gasket,the mechanic didn’t seem to know and kept the car for a week.

please help he didn’t do a coolent test I don’t think.

I read so many things like it could be reservoir cap or thermostat.

Im so worried as I need car for work and don’t really have money for big repairs.

thanks in advance for the help.