I have a 1991 Montero with V-6 it has started to leak a lot of water from the back of the engine..I can not see where it is coming from..but can see it running onto the bell housing of the trans.. this leak will drain the cooling system in about 5 minutes.. the heater hoses look ok

 

You have a leak in your water cooling tube.

 

Sounds like your water cooling tube that runs across the top of the engine has a hole in it.