Hi folks, your much needed advice please:

I have a problem with my Punto loosing coolant and wanted to know the checks
to carry out.  Here's the symptoms:

1.  Coolant needs topping up every 50 miles or so.
2.  In car heaters have been blowing cold sometimes (dired result of low
coolant I think)
3.  When car overheats - all systems seem to react accordingly, i.e. light
on dash, power dies, fan kicks in (all be it a little late).
4.  This happens on both long and short journeys, although now I'm keeping
mileage to a minimum until this is sorted.

Here's what I've done:

1.  Treated with Radweld 1 week ago, but level has dropped again
2.  Checked for head gasget problems but cannot see it is that, as in no
'mayonaise' on the oil filler cap, cannot see water on the dipstick and no
signs of water vapour coming out of the exhaust.
3.  Had a machanic check the radiator for leeks but to no avail.

Has anyone got anymore suggestions please before I fork out for a new head
gasket?