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Anthony, ASE Certified Technician
Category: Nissan
Satisfied Customers: 11750
Experience:  ASE Master Automobile Technician with over 18 years exp. in this field.
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my 2003 nissan sentra 1.8 has great heat until i stop or idle,

Resolved Question:

my 2003 nissan sentra 1.8 has great heat until i stop or idle, then when i drive it gets hot, there is a new water pump, new radiator, new thermostat. my mechanic thinks its the head gasket because there was a little white smoke coming from the exhaust. i bleed the radiator right but there is great heat until i stop at an idle. the temp gauge is perfect but i notice when i fill the radiator up full, the car runs cold, it seems i have to drain a little antifreeze out to find that perfect air gap to get some heat, well now there is no heat. my question is, even though it looks like i need a head gasket, is it possible i also need a heater core, by the way, i by passed the heater core and both hoses were connected to eachother and both remaqned equaly hot while the car was running. what do u think and please tell me is it hard to change the heater core, is it ubder neath the glove box or is it the hard one under the middle of the dash, please be very specific.
Submitted: 7 years ago.
Category: Nissan
Expert:  Anthony replied 7 years ago.



Does the car need coolant added after a while?

If so how much?

Customer: replied 7 years ago.
no. the car is at a steady tempature, i added bars leak with the thermoatate hollowed out and the heater core hose clamped and ran for 1 hour. it seems the car runs normal and blows hot when the radiator isnt fully filled bit once filled i seem to create a air pocket and then it blows cold. should i go for the heater core first and is it hard on the nissans or is it easy (under the dash)
Expert:  Anthony replied 7 years ago.
The core was probably plugged from the bars leaks. The head gasket is more than likely compromised though. The dash has to come out to get the heater core out and its a big job. I wish I had better news. I would try flushing the heater core out both ways with a garden hose and see if you can get it flowing again before tearing into anything.
Customer: replied 7 years ago.
i did flush the heater core out and it seems fine water ran through great but does that always tell if it is clogged, and the haynes book shows it pretty easy on the 2003 nissan, are you sure i have to ripp the whole dash apart
Expert:  Anthony replied 7 years ago.
Its the evaporator for the AC thats easy, not the heater core. If water runs through it easily, its the air pockets from a partially blown head gasket.
Customer: replied 7 years ago.
im ready to pay just 1 more, would the air pockets from the head gasket cause the car to blow out hot while driving then cold from a stand still the later blow out cold all the time. and could the heater core be partially blocked with water still flowing with a garden hose in it?
Expert:  Anthony replied 7 years ago.
No prob. I would like you to be happy with my help. As for the core that does flow, its good almost 90 percent of the time. See a bad core has no heat at idle then makes heat when you rev it up all the time. Air from a bad head gasket acts like yours which is inconsistent like you describe.
Customer: replied 7 years ago.
but here is what is confusing, if i fill the radiator all the way and then drain about 2 cups out, then i find that certain sopt and the car has great heat when i stop though, it goes from hot to warm to cool to cold, but once i give it gas it heats up right away or when i drive it has great heat, that was the deal today but when i bypassed the heater core about 2 hours ago, and the ran a garden hose through it, the flow seemed fine but once i put the hoses back to the heater core, the car blew out hot as usuall but cold at stand still, but i thought i spilled out alot of anti freeze while bypassing the heater core so i added antifreeze to a complete fill, and then the car ran cold all the time tonight. what do u think, and this is last question
Expert:  Anthony replied 7 years ago.
Ok, you have some air trapped. Have a shop use a vacuum filler to do the antifreeze. Manually filling it does not get the air out all the way. I use this tool on all vehicles for the past couple of years so I never have air. But your vehicles cooling system instructions say to only use this tool. Any jiffy lube or shop with the tool can do this service.
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