my blazer has a heater core bypass,and has rust in the cooling system and i took the termostat out and my macanic said it should run cooler but when i get on the freway it will go all the way to red...and the bottom part of the fan shroud is missing...what to do?

 

First I would recommend you flush every part of the system to ensure that there is no more junk in there. Then put the thermostat back in. The cooling system is made to operate with the t-stat in there. Coolant needs to be in the radiator for a bit to cool it down properly. Free flowing through the system will cause the condition you are experiencing.

BTW, please provide your vehicle information whenever you ask for help!