When I bought the Taurus in June of 1992, I noticed the rusty color in and around the coolant reservoir. I had checked a lot of car web sites, and the Taurus got good marks, so I thought no big deal, I'll get the radiator flushed. But, when I took it to the Ford dealer, they checked the water with a litmus paper, and said when they get the reading they got, Ford recommends having a "heater bypass hose" installed. Also recommended to be replaced at the same time for the same reason, was the water pump and freeze plugs.
Because it would have cost more than 1000.00, I said just flush it, and I'll take care of the heater bypass hose. Turns out it was way too involved for me to tackle. I did some more checking on the web, and found a lot more on the problem of rust in the block. I know that Ford started installing them at the factory by 1999.
If you're thinking of buying a 1998 or older, make sure the heater bypass hose has been installed. The car did fine without it till the transmission quit working in first and reverse at 91000 miles. I've talked to four mechanics, including the Ford dealership, and they all agree that the trans axle probably needed replaced.
On a lighter note, the mileage was great, 30 miles a gallon on the highway at 70.
There's quite a bit of road noise in the cab, but it's fairly comfortable.