well...try these ideas out...
it COULD be that ur thermostat is stuck closed, try heating up ur motor, an then check the temp of ur upper radiator hose. it SHOULD be warm.
check ur electric coolant fan blades...if they're cracked or broken, this could also cause it...
last couple ideas are that ur ignition timing is off...causing overheating (its stretching, but it COULD be it..)
try those three things out...