www.howstuffworks.com There is a whole slew of articles under the auto tab. You should be able to find your answer there
ww.ask.com I just checked out about ten sites! It was way to complicated for me to explain.
www.ask.com ~Sorry!
You already asked the same question, if you don't like the answers...maybe you could search for yourself. maybe.
sorry, i was looking for a picture of it and i couldnt find any ont the web so i asked here.