Why would your 1995 Buick Skylark Quad 4 be overheating Also what size speakers do you need to change all 4 and which are best?

If you have replaced the thermostat already, and the radiator is flowing properly, I hate to tell you, but the quad 4 has a nasty reputation of cracking heads around the exhaust seats. Be very careful in getting this repaired; make sure the shop that does it has had experience with this motor.