coolant leaking help please
 

i have a 90 ls and just recently ran into a few coolant leaks. i have replace the radiator, lower and upper hoses and also all the hoses behind the intake manifold. but i am still leaking coolant somewere and somehow but my overflow tank and radiator never show low or show any signs of it loosing coolant. it is running down the back of the block and dripping down onto the exhaust. it only appears to leak when im at idle/red light and as soon as i go the smell of hot coolant goes away...my temp gauge reads under half and never rises so can anyone give me some ideas of what it could be?