Yah, the rear does that, its normal.
In a Canadian winter, its not unheard of to use an entire bottle in a day. On top of that, its deadly if you run out. If its a busy highway, the last thing you want to do is pull over and throw snow of the windshield every 10 miles. Its very important to know when you run low, so that you can conserve till you get to a gas station & buy some.