I just replaced thermostat and veh still running hot?Why?

Also could have a clooged heater core,remove lines flush with water both ends

One make sure the thermostat is installed with the spring inside the engine. Second make sure your fan is coming on when turning the AC on. The fan runs anytime the ac is turned on, even with engine not running if the key is on and the ac is on, the fan should be running. There is a secondary unit that turns the fan on when the temp reaches around 220 degrees and has nothing to do with the ac. This unit is located at the left front side of the block near the top and looks a lot like the temperature sender on the manifold further up. If your fan runs with the ac on make sure it sounds as if a 747 is taking off, some fans are worn out and barely run but by looking at it you think it is working. The fan motor is easy to replace and you can pick one up for around 28 dollars. You can leave the ac off and let the car run until it gets hot and see if the fan comes on, if not, replace the temperature sensor unit, not the temperature sending unit for the gage. If the fans work the way they are supposed to, then you need to have the cooling system flushed and cleaned by a professional cleaning company.

Hello tbrink. most likely your water pump is not running like it should resulting in it running hot. To test it do this: Get your car up to operating temperature, run the A/C. Once the temp is about 80-85 deg. Park it and let it sit idling with the A/c on for about 5 minutes, then turn the car off. let the car sit for about 5 minutes with the engine off. Then turn the ignition so that the temp gauge registers. You will probably see it spike to over 100 because the car has been sitting with a hot engine and no coolant flowing through to take away the heat. Note the temp, then start the engine. If the temp doesn't come down to normal within about a minute, then you probably have a bad pump. When functioning properly, as soon as the car is cranked the pump will move enough coolant through the head to drop the temp very quickly.

Joe