water loss?

on my v230 i loose water but no sign of a leak.Also theres a misfire when it starts from cold, could it be the head gasket?...the oil is clear of any mayo in the oil cap, and coolant is clean also.I've changed the plugs and leads,water pump, radiator, and thermostat...is there anything else to check before going down the head gasket route?

Cheers.