1995 Chrysler LHS

Engine Cooling problem
1995 Chrysler LHS 6 cyl Front Wheel Drive Automatic 139000 miles

What would cause my engine to overheat severly one day but not the next time it was driven.
It seems like it's an intermittent problem, but on occassion, it happens back to back.
Thank you for any advice.
May 30, 2009.

Replace the thermostat and see what happens

May 30, 2009.
Thanks! That's the frist thing I tried before I asked for help. I've since then replaced a lower hose, flushed & * refilled. Bled system, verified waterpump was still good, (just replaced last yr.), Checked fans, air cleaner, so 0n & so On! No leaking heater core, exhaust clean & no moisture, oil very clean & proper, (has been changed every 3,000 since late 95.) No oily or trans fluid in coolant drained or at any trime. Fan clutch working fine, belts just replaced last yr. Radiator not leaking, cleaned of debris always, & no hot or cold areas unevenly. Cat converter fine. No timing problems, or vacumn leaks detected.
About as thorough check as I can do with some help of course. I'm a 53 yr old woman. No to bad huh?
But it's getting the best of me. Now I need to know where I should go from here & I would greatly appreciate any more advise or suggestions.
Thank you for your quick reply.

May 31, 2009.
Could be air in the cooling system try bleeding it

Jun 1, 2009.