85 tercel 82K miles on motor here is the deal. Sometimes after setting at idle for a while in stop and go traffic it will start steaming out the exhaust, can't hardly see behind you then it will stop steaming out exhaust, and when I check the antifreeze the overflow tank will be empty radiator full. It may not do this for weeks, then it may do this 2 or 3 times in a row. Machanics are scratching their heads like me. any ideas

alright... blown head gasket ?

or... yeah. my car sometimes mysteriously eats coolant. i drive a 1990 tercel. i just fill it back up and don't worry about it. just keep an eye on your oil because by the time the coolant shows up in the oil it may be too late

Have you had the cooling system pressure tested?

Yes it has been presure tested, no leaks found. Also dye tested, no leaks found. This has not been done while smoking though, never know when it's going to smoke.