We replaced the relay switch, we replaced the fan motor, thermostat, and by passed the fan switch, and it still over heats with cap on, is good with cap off. If you know what the problem is please answer this.
Thank You.
It is a Chevy Cavalier 1994 3.1V6
could be a clogged radiator that cant handle high pressure not sure try getting a flush
hey thank you. we are going to try that monday. thanks 
are you experiencing loss of coolant?
Corroded radiator fins, many are gone, inspect from rear. If over 5% are rusted away, the radiator is bad. Don’t even flush the old one unless it passes inspection. Check it from the rear. Good with cap off? Could be a blown head gasket.
Find a radiator shop in your area, see if they still rod radiators, if so, take it to them and have it rodded. You may have to replace the core. This will be cheaper then replacing the whole radiator. Also try installing a new cap before going to the shop, the old one may be weak and be all that’s wrong. Good Luck.