Cars were lined up more than 20 deep around lunch time at an automatic car wash on Signal Mountain Road.

If you wash your car when it's below 25 degrees, the dirtiest places under the car remain frozen.  That's where rust can form.  

It's best to go back after the temperatures climb, according to the International Carwash Association.

Even Thursday some car wash places were still closed.

And one more tip, remember to dry the car, especially around the trunk and hood where water collects