2004 Chevy Optra Coolant

Hello and thanks for donating

Sorry for the slow response

Normally when the coolant is leaking slowly but there is no visible signs of leakage anywhere that is a good sign of a cracked head gasket. The coolant could be seeping past the cylinder head gasket and being burnt in the engine and blown out the exhaust either as white smoke or if it's a very small leak you may not even notice smoke at all. You will want to have a compression test done on the cylinders to check for a cracked gasket.