My newly purchased used 97 Saturn SL1 over heats going up our very steep 1 mile long dirt road. You have to drive very slow because of the road. On regular roads no problems. I checked for leaks but have not found any. The water in the overflow bottle steams like crazy when you stop at the top of the hill.Any ideas on what wrong?

Radiator cap may be bad or the cooling fan may not be working...try this start the car and let it run in park open the hood and wait for the fan(s) to start... the gauge in the dash should not be much higher than half way before the fan starts... if the fans don't start before needle is 3/4 the way up the gauge it could be a the coolant sensor is bad and not telling the computer to start the fans the sensor should be on the engine near the water inlet hose from the radiator

Real bugger?????
it has a plastic pop-on connection and one socket takes if off and on, heel its even in plain view
a blind monkey could replace it....

Mrdrchad203 is right. It could be the Engine Coolant Temperature Sensor, and it is located to the right of the radiator hose on the driver side end of the engine. There are 2 sensors in that area. The one that is on the left and slightly higher than the other is the Eng. Cool. Temp. Sensor...it controls the fan. The one that is to the right and slightly lower is the Engine Temperature Sensor, and it controls the gauge on your dashboard. If this doesn't correct the problem, it could be your water pump...unfortunately you cannot take a cap off the top of the radiator and look in to see if there is water moving. Replacing is is a real bugger and unless you are a "fair-to-middlin'" mechanic you need to fine a reliable shop and have them replace it.