Eternity comes to mind.... Although the goal from an emissions standpoint is to bring it up to temperature as quick as possible, idling does not do that as there is so little work involved.

The heater core, a liquid to air heat exchanging needs hot coolant in it for the heat to be extracted. Hot air does not have enough thermal mass to heat the air.

Although your engine is not currently overheating, steam through the core won't heat the cabin! Verify the block is full of coolant.

 

So what affects the gas mileage?
and thanks for the coolant tip

How do you check the fluid level?
I am a young female college student. Lol

 

Look at this link. If you don't feel confident get one of your college mates that are mechanically inclined to help. The last thing you want is for your car to over heat.

The car will have bad gas milage in Winter. Plus many other reason for bad gas mileage also, bad sensors, plugs, etc...

https://www.carcarekiosk.com/video/2..._coolant_level

 

How far is your drive? If less than 5min you'll likely not have optimal MPG's.

 

This cars are such a PITA to warm up in Winters, Takes me like 15 - 20 minutes of driving to get to full engine temp. Then, the idle will drop to normal from 1100 rpm's which mean more wear on the brakes. WTF!