2003 nissan sentra gx 1.8 no heat comes out just cold air. when you hold the 2 heater hoses from the eng. to heater core one is hot and the other hose is cold. is this a heater core bad or something else. please help

let the engine warm up to operating temperature. turn on the heat full blast. feel the two hoses going to the firewall to the heater core; if they are both hot, then your problem is in the heater box or heater controls. if one hose is significantly cooler than the other, then you have a clogged heater core and you can replace it or try and backflush it.

Check the heater hose's going in through the fire wall ,are they hot ? Both hose's ! This is something you can do yourself ! If they are hot probably the temp actuator is bad or the door is stuck on the cold or heater core clogged ! Video's on youtube showing what to check. Learn to double check your mechanic !
How to Fix Car with No Heat Easy

remove both hoses from engine that passes through firewall to heater. put a stiff piece of wire in the hole and make sure it is clear. If there is no restriction, then the heater is choked up

Are you talking about the engine cooling system or a problem with your Auto A/C?

The problem is likely in your heater case doors, not the core itself. These doors are either vacuum operated or small motor operated.

Get the car warmed up, then feel both heater hoses. Both should be hot, meaning coolant is circulating. If only one is hot, the other cold, then you have a circulation problem.

has to be air bound.with vehicle running but before it gets too hot remove outlet hose from heater core at bulkhead.wait for consistant waterflow out of hose then reinstall and top up system.now the bad ....where did the air come from?these engines are becoming notorious for head gasket failure.does it ever miss and run rough for fist few seconnds after a cold start?if so this is probably your issue.

Sounds like it's the air control flap which determines the mix of heated and fresh air. This could be vacuum controlled or manually with a cable.

My 2005 Nissan Sentra 1.8s with 55,000 mi. blows cold air from the heater. Coolant not circulating in engine. Lower hose stays cool to touch. Both heater hoses cold. Changed thermostat - didn't fix it. Coolant not leaking or dirty. None in oil - no oil in radiator. Changed worn water pump belt - pump spins freely with no noise or resistance. Cooling fans come on after warm-up. Temperature gauge stays in normal range then jumps to hot and back again. Coolant good to 10 below - didn't freeze here yet. No other problems or repairs to car. Afraid to drive and make worse. Help!

My 05 sentra with 79k miles heat will warm up and then get cold after a mile of driving, we have tried to get the air pocket out, the mechanic stated he thought it could be a blown head gasket, another mechanic said it was a bad heater core. Any advice would be appreciated.

Your blend door in your car isn't functioning properly. The blend door is a part of the box that your heater core is in.