i warm up my car for 5 minutes 5 days out of the week and let me tell you...it really kills your mileage...i averaged about 18mpg on my last tank. that means it is 25 minutes of idling a week, sometimes more because i let the car idle outside while im finsihing my shit, lol.

my car is old and i drive only a couple blocks. not good for the engine because it never gets a chance to fully circulate the oil.