My 1998 2.6 V6 Contour rapidly overheats. I have changed the waterpump and thermostat and bottom hose, all to no effect.

No, there is no oil in the water or water in the oil, no smoke, no coolant loss, no oil loss. I read somewhere that the lower hose had a tendency to delaminate on the inside and thus collapse under pressure so I replaced it. This has been an ongoing mystery. Two waterpumps have been replaced, one with a bad bearing, one with bad plastic vanes. I would replace the radiator if there is a possibility the plastic vane debris could be causing a blockage, but that is a time consuming job.

Have a pressure test done to the cooling system, any shop should be able to provide this for you. That should point you in the right direction. Post findings!!!

Thanks for the tip, I will do that and post the findings. Thank you for your responses too.