Can other posters (I mean Deggers here, by the way) remember that the question was put on because cris doesn't know the answer? There is no need to be so condescending - I presume you had to find out these things yourself as I doubt you were born with a priori knowledge of the internal combustion engine. If you start to demean people for wanting to know the answer to a question then you undermine the whole point of theanswerbank.
PS - Toureman is correct that you should be checking once a month at least and always before a long journey.