Leaks can be wherever two surfaces meet as coolant passes by.
Under radiator on bottom left, should be a plug or a screw.
Find the leak and replace the hose/part that's leaking. It's a good time to flush your coolant system, too.
Mine is a '92 and the sensor is screwed into the back of the radiator on the passenger side about halfway down.
Right under the battery
I'm assuming your grand am has a 3400 v6 which are known for intake and head gaskets leaking. so its possible that one of those gaskets are leaking so bad that coolant is leaking from intake/heads down onto your valvetrain and then down into your oil pan. more than likely its your intake gaskets leaking.
You may have a blown head gasket. Have it pressure tested. The head gasket keeps the cylinder head sealed from the water that circulates through the heads to keep them cool. If the gasket gets a hole in it, then there is a gap in which oil can get into your coolant. Make sure what you are seeing is OIL in the coolant first.
Should be in a removable housing at the engine end of the upper radiator hose
You may have put the thermostat in backwards, which would restrict coolant flow. Also, look at radiator inner cores for signs of buildup. If so, replace radiator, it's cheaper than repairing the radiator.
It's up on the thermostat housing. Follow your upper rad hose to the thermostat housing.
Should be located in a removable housing at the engine end of the upper radiator hose Drain about 1 gallon of coolant from the radiator Remove this housing Note how thermostat is installed in housing Clean both surfaces Replace thermostat and gasket Replace housing Re-fill coolant slowly to prevent an air lock Start engine and look for leaks Run engine to normal operating temperature with heater on Re-check coolant level
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I had this problem and the manfold gasket was leaking I am aware of sensor issues with this but I has to replace the manifold gasket problem solved.