why would my jeep be overflowing coolnt last time it did it was when I went offroading

If it has only done it that one time,it may have been just over filled,or possibly the top was not on tight and it spilled out.

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MDJeeper = Aren ( Crazy Ass Old Marine)

The radiator cap... the actual one on the radiator itself (THE HOT ONE!!) probably has a leak under pressure. I'd imagine it 'seems' tight, it you check it, but after warm up it's letting out too much pressure.

There a 'figure' there (which I'm not going to 'go figure' right now!) for every pound of PSI in a system the coolent's boiling point is 'upped' by several degrees. It's sounds like it's 'boiling' too soon from not keeping good pressure. Of course the pressure leak could be anywhere in the water jacket... only most likely the cap.  

There is another 'course of action'.... remove the radiator cap and drive a new JEEP under it!   

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Big & Bad Yeller Muddin' Machine Thang!