Usually twice a week for my Tbird- daily driver.
There's just too much dust and too many birds around here.
My Cougar is babied like crazy.
Washed mabey 3 times a month. Usually Drove less than 200 miles per month. Garage Kept. Always kept under my fancy schmancy mucho expensive car cover.
My Mustang, well thats another story.
I am prepping it for paint right now, so it will basically get it's first good wash right before the primer goes down.
I usually wax my daily drivers once a month, my Cougar - right before shows and as needed since it doesn't see much road time on a regular basis.
Full Detail is done before shows/holidays/special occasions; Or, whenever I get bored and decide to do it.
Interior on all my cars is gone over weekly to bi-weekly depending on need.
Keep things looking nice in between with Meg's Final Inspection, Auto Magic Tire Shine, Stoner Glass Cleaner, Mothers Mag Polish, and a crapload of towels.
