01 Honda Accord overheating

I just bought a 2001 Honda
Accord coupe (218k mi) 3 weeks
ago, from a mechanic that said
he changed the timing chain and
water pump 10k mi ago. About a
week ago I was sitting with car
parked and running for about
10mins, and when I cut it off I
heard gurgling water noises
under the hood then notices it
was streaming. All the coolant
was gone from radiator and
reserve. I let it cool off, filled it
back up with water, left radiator
call loose, drove home, and temp
gauge never went above a little
less than halfway. I've been
driving ever since daily, checking
the fluid which is still full. The
temp gauge never goes passed
the halfway mark though. The
fans only come on when I turn the
A/C on. It's cold out right now so I
know when I'm driving that helps
cool the radiator, plus I keep the
heat on (high is I can handle it for
awhile) because I've heard of
your car starts to overheat turn
the heat on high, so I just keep it
on.

Any idea what it could be?!?