Each year when the temperature drops below 10 degrees F, I notice that the level of antifreeze drops more than usual. This has occured on the last 3 cars I have owned.
I drove the car on a 7 hour trip and the antifreeze level stayed the same. Within a week the temp dropped to 6 degrees and the antifreeze level dropped a couple of inches in the over flow. There is no antifreeze under the car and the heater core was just replaced and it doesn't smell like antifreeze or steam.
So, why does the antifreeze level drop significantly on the coldest day of the year?