Cadillac STS

I just bought a 1995 Cadillac STS, the guy I bought it from said it was in good condition. When I was driving it home it overheated. WHy is the car doing this. Also, when I open the door with the key to the car the alarm goes off and I dont know how to make this problem stop either. Please help. Thanks Krissy
May 23, 2007.

Try replacing the thermostat-not it do the following below: Have it block and pressure tested-do the block first to pinpoint a combustion leaking into the cooling system or a gas analyzer to sniff for hydrocarbons at the radiator fill neck.

Pressure test: do not do a pressure test if there's leakage at the headgasket this might cause coolant into the cylinders and lock it up or bend a connecting rod if cranked thereafter. The headgasket should be repaired before doing the pressure test.

If the block and pressure test passes check the following: Thermostat, Pressure test the Rad. Cap, Clogged radiator, Fan clutch, Radiator electrical fan, collaspe hoses, water pump.

May 25, 2007.