My first engine blew at 70,000 miles the warranty company installed a new but used engine they said it had 56,000 miles on it. And it overheats with the AC on at high speeds. Not sitting at stop lights like an old engine or clogged radiator but at 65 to 75 up hill or straight away. They have receipt of a new thermostat and the antifreeze is green and not yellow. (I'm not sure what the difference is anyway) but something is wrong, The shop that did the engine thinks there is a plastic bag in the grill and I assure you there isn't can anyone help with this?