Help - Head gasket gone?

The history:

Had the radiator replaced a couple of months ago - about a week later temp guage went into the red - hose hadn't been replaced correctly & it rubbed against a fly wheel (I think that's want it's called) Anyway RAC man repaired hose & I had it replaced properly a week later.

Since then it has been overheating - there doesn't seem to be much coolant being lost.

If I undo the expansion tank the coolant spills out even when cold but if I undo the plug on the top - not the radiator one but the one on the metal thing the hoses go to (sorry don't know what it's called) it lets the pressure out then open the expansion tank cap & the coolant level goes down.

The thermostat has been replaced & the heater is really hot but if I say drive 10 miles then stop turn off engine then start again after a while after about 4 miles the heater will go cold then the temp guage shoots up. Once it's cooled down enough to take off plug on top and expansion tank & let the pressure out it will be fine for the rest of the journey - I only ever go about 35 miles & it will do this fine provided I let any pressure out before setting off.

Is this likely to be the head gasket or could it be something else?

If it is what is the likely cost of fixing it?

sorry it's long winded....

check to see if oil and water are mixing, look for a creamy build up on the oil filler cap / dipstick (wait for the punns to come in....)

get a sniff test done on the water, most garages should be able to do this and its not a big job so dont let them fob you off with high prices as all they do is put a syringe like device in the expansion tank to see if it changes colour (indicates hydrocarbons in the water)

or you may be making a mountain out of a mole hill and just have air locked in the system, make sure its properly bled with the heater controls on hot to ensure you have a good flow running through the heater matrix

keep us updated

Many thanks - I have been suspicious that's it's an air lock as it only started after the hose went but it has been emptied and re filled with coolant since then - what is the best way to get any air out the system?

Could the over heating have caused the head gasket to start leaking?

I hope that's all it it.

Overheating could be a contributing factor but it depends on how long it was ran when overheating..... But you don't know if it has blown it yet..

As for bleeding it, put the heater on hot (not the fan) get it running in tick over and find the highest point (there may be a bleed valve) and basically treat it like you're bleeding a radiator at home

They can be a pain to to bleed - few threads on here about best ways to refill

Here's one of them

http://www.landyzone.co.uk/lz/f8/radiator-heater-bleeding-68669.html

loads of others if you have a search