If you don't have an obvious coolant leak externally, then you have a huge air pocket in the cooling system! The A34s are notorious for this issue and there is an actual Nissan TSB on this too. We have a special coolant tool that removes all of the air out of the system and what's left? Vacuum. One end of the hose goes into a 50/50 mix of coolant and you just turn the handle on the tool to suck the fresh coolant in...
