My Sable is having several issues and I can't tell if they are related. The car is driven less than average, three or four days per week. At some point, it lost coolant and I had to add about two quarts a couple weeks ago. The engine is still hot right now, so I'm not sure if it's low at the moment. Another issue is that the speedometer will sometimes drop to 0, seemingly randomly, while driving but will eventually return to a working state. When the speedo starts working again, the car makes a strange noise. The last issue I have noticed is that the car sometimes has an issue accelerating. You can push the car to 5 or 6K RPM but the car will still travel at, say, 15 MPH.
Having owned a 97 Taurus which is a Sables cousin a common problem is the vehicle speed sensor. If the sensor completely fails it is easy to diagnose. Mine slowly failed over a two week period during which time it would shift into nuetral, have eratic speedometer readings,and would shift up or down at odd times or work perfectly fine. The coolant resevoirs are also a high failure item. They develop a leak at the bottom so it makes it difficult to add coolant. When I replaced the coolant tank a new one at the dealer was $3.00 more than the salvage yard wanted for a used one.