Overheating?

Me, my cousin and one of his co workers went riding around up in the mountains this morning doing a little pre season deer scouting and when we got to the top of the mtn I noticed my jeep started sounding funny...
We pulled over and all of a sudden steam was everywhere, the temp. gauge was only at 145*-150*. When we popped the hood I noticed the radiator jug cap was off and I immediatly knew it overheated...but why was the temp. gauge at 150* when it did instead of the 260* mark?

We let it sit and cool off then filled up the radiator jug to about 1/2 full and put the cap back on and went home. Well after about 4 hrs it had cooled off so I figured things were back to normal but I was wrong. I took a little trip to check out some land we have leased for deer huntin and figured this would be a good time to see if it was gonna heat up again. Well when I got about a mile from my house I noticed it heated up really quick to where it normally runs, about 130*, then to 150*. It never got any hotter than 150* during the entire 12 mile trip but when I got home I popped the hood to check the water level in the jug and it was at about 1/4 full.

Could the water pump be goin out, or could the thermostat be fudged up or is it somethin more serious? And why did it go from 100* after cooling for 4hrs to 150* in about 3mins? It hasnt got that hot since about this time last year when the water pump and thermostat went out.

Sounds like a vapor lock. A pocket of air around the sender keeps it from reading right, or the sender is TU.

Replace the radiator cap.

Sounds like you might need a new temp. gauge. Also try burping your cooling system....you may have an air pocket. If your water pump is working you should be able to see the water flowing into the bottle (if you have a turtle) while at idle and increase flow if you rev the motor a little. If burping the system does not work definately check the pressure cap for the bottle. If the pressure cap is bad you could replace the whole cooling system and it wont help. Go get an OEM cap and maybe even an extra to carry for cheap insurance.