What are other ways to find out if you have a bad thermostat? on 1994 Cadillac DeVille

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My car over heats and i replaced the radiator and coolant resevoir. I have also replaced the thermostat but it seems to always over heat. Could it be a faulty thermostat.
(2) Answers
Does your radiator fan work when you turn on the A/C, because it should. If not, repair your cooling fan. Does your car use any coolant? Has it been pressure checked over night to see if there is a weep hole leak in the water pump? The head gasket should also be checked for any leakage by checking for HCs and CO in the cooling reservoir bottle or you can use a block checking kit. I would have a pro do this to be sure of the results.