Volvolious-J,

All the responses you received are possible causes of overheating. Yes, the radiator cap and a bubble in the system can cause the problem. But, you've got more going on than that.

The symptoms you reported:
Gauge usually reads high but on one trip went very high.
Since then, no indication of heat and no heat from the heater.
Steam from under the hood on more than one occassion.
Observed dryrot cracks in upper radiator hose. Observed leaks from the same area.
Observed overflow/vent pissing on the ground.

I would not drive the car until the cooling system is repaired. An overheated engine does not live long.

You have a neglected cooling system that needs normal wear items replaced before you do anything else. Order new: water pump if needed (see Derek's post), radiator cap, all hoses and clamps, and a thermostat with gasket. While you are waiting for the parts to come in, pressure test the radiator and heater core. If you need instruction, just ask on this board, you will get help.

To flush the block you can get a "kit" at any auto parts house. It connects inline with one of the heater hoses and connects an ordinary garden hose to back flush the block. Let the water run until it runs clean.

Your posts lead me to think that you have little or no experience working on your cars. That is not a slam against you, no one is born knowing these things, you only learn by doing. The very nice folks at http://www.volvoamazonpictures.se/ have posted the Green Books for the Amazon available for downloading. Get the one for the engine and read the part about the cooling system. If you need help maybe someone you know can help you. We can help with information but you have to do the work.

Post back and let us know how it is going.
--
Mr. Shannon DeWolfe -- (I've taken to using Mr. because my name tends to mislead folks on the WWW. I am a 51 year old fat man ;-) -- KD5QBL