Q: why would coolant come out of reservoir when temperature gauge just above middle on 1999 Oldsmobile Cutlass

Rookie cbe0621eac06868b3efe0d8d1d3611e23c60d3114864ea2ec19a68cfbd3eebab
I have replaced the coolant temperature sensor. The cooling fans do not come on. Have checked all fuses and relays related to the cooling fans. Have disconnected the temperature sensor while car running, both fans cotme on high. when reconnect the coolant sensor the fans stay on low, once car is turned off coolant sensor connected and restarted the fans do not cycle through and come on. I have heat. Help please
(4) Answers
You need to stop driving the car. Tbone1980 is correct. Depending on how severely you have overheated the engine will determine the course of repair.
There is a test for that before you do anything! Contact a repair shop and ask if they can do a COMBUSTION LEAK TEST, that will accurately tell if any CO is entering the cooling system, have this test performed FIRST! Also the thermostat on this engine is a pain to change, bet it has never been done! Now I assume this is the pushrod engine and not the SOHC 3.1 offered in the Cutlass/Supreme?? One more thing, have you replaced the coolant fill cap? If not do so and make sure this NEW 'threaded' cap is tight. Temp. Just above 1/2 WAY, is not HOT. Fans might come on if all this is corrected!
unfortunately these engines are known for bad intake manifold gaskets, the coolant in the block is being over pressurized by exhaust gasses escaping into the coolant system, You will need to have the intake gaskets replaced but you may also want to replace the head gaskets as well as they may have been damaged form overheating, but first start with the easient thing and change the thermostat first,if problem continues then proceed to the head and intake gaskets...
Qualified Local Oldsmobile Shops
Qualified Oldsmobile Shops For This Repair