If your air doesn't blow out warm while you are at idle these steps may help you.
Nissan actually has a TSB (Technical Service Bulletin) about it.
If you want all the mumbo jumbo you can get a copy from your Nissan dealer.
The number is NTB02-047c (or that's the latest version as of this writing)
The first step.
Nissan says the coolant mixture must be between 50-55% ethylene glycol based antifreeze and water. While it's true that too much antifreeze will reduce the mixture's ability to transfer heat, I don't share their thoughts. But they are very adamant about it.
They even go so far as to have you test the coolant with a REFRACTOMETER.
A special tool that uses light to "see" the density of liquid. Cheap ones are around 80 bucks.
So if you want to believe that the ratio really does have to be perfect. Then it would be cheaper to drain the coolant and fill it with a perfect 50/50 mix. And if you car has over 50,000 miles, you should do it anyway.
The Second step.
You probably don't have the system bled correctly.
Some guy (or woman) came up with a really cool tool that looks like this.
It attaches to the fill neck of the radiator so you can have a bunch of fluid above any other point in the cooling system. I have one, but I don't expect you to.
So now we get to "McGiver" one ourselves.
Fill the radiator SLOWLY as much as you can.
Do it slowly so the tiny bubbles in the radiator core can work their way up to the top.
I give the upper radiator hose a few gentle squeezes, it moves the water back and forth to help get the tiny bubbles moving.
After you get as much water in the radiator as you can, it's time to pull out the duct tape and bailing wire.
Get a metal coat hanger, and pliers.
Snip off a little more than an inch and bend it in a shape of a "U"
Were going to be putting it under the vent valve in the radiator cap.
Don't make it too big or it wont fit down in the hole we need it to.
Don't use anything skinner than a coat hanger. The valve has to open wide enough for air and water to pass through it quickly.
Now put the radiator cap back on with our U wire installed.
And take the reservoir tank hose off of the fill neck.
And it's time to make our "tool"
Use a clean empty jug (one of the left over antifreeze bottles will work great)
Find about 3 feet of hose that will tightly fit on the port on the fill neck.
Cut or drill a hole in the bottom of the jug smaller than the outside of the hose so it will make a good seal.
Stick a couple of inches of the hose into the bottle, you can even use some the antifreeze as a lubricant if it's too tight.
Use the left over wire from the coat hanger to hang the bottle from the hood latch hook.
Attach the hose to the port
Use some ViceGrips to clamp off the hose
Fill the bottle with... you guessed it 50/50 mix (have I said that enough yet?)
And you should have something that looks like this.
A step ladder will be helpful right about now.
Set the parking brake, and block the rear wheels.
Jack up and support the front of the car with jack stands, the bottom of the front bumper needs to be at least 22" off of the ground to get the air bubbles to go to the radiator.
If you've got a helper and a cold drink, it will make the next step pass a little faster.
While keeping the bottle tool full of... say it with me. 50/50 mix.
Get in the car.
Set heater controls to maximum heat.
Mode switch to floor/defrost.
Fan set to HIGH.
And start the engine.
Remove the ViceGrips from the small hose.
Run the engine at 1500rpm, giving it a little rev every now and then, until the cooling fans come on.
Somewhere along this time, the thermostat is going to open so expect a bunch of bubbles in the tool and the fluid level in it will lower. Make sure you keep it filled.
And keep an eye on the temp gauge too.
After you don't see anymore bubbles you can turn the engine off and start cleaning up.
But MAKE SURE you let the engine cool off enough before you start playing with anything. Antifreeze is sticky, if it sprays on you while it's hot, well, think of napalm.
Lower the car.
Crimp the hose.
Remove the homemade tool.
Pour the 50/50 mix in a bottle to keep for a later date.
Reattach the reservoir hose on to the filler neck.
Take off the radiator cap and remove the U wire.
Top off the radiator.
Check the cap for any deformities in the rubber seal and put back on radiator.
Start car and check for leaks and to verify the heat is cooking you out of the car.
Enjoy the winter.
EDIT: god i just can spell to save my life...