Conventional oils have solvents that stick to gaskets and seals and often cause them to swell a certain way. These gaskets and seals have been used to the same oil for years and the switch to any other type of oil (whether it is to a different conventional oil brand, or an upgrade to a synthetic) may be harmful. The oil you change (or upgrade to) will also have solvents and additives, different from the original. So in other terms, the changing of oils could result in oil leaks and/or a once small oil leak becoming bigger due to the reaction the seals and gaskets will have to the change (not because of the oil itself). If you think that this might be the case for you (i.e. if you have an older car using conventional oil), it’s recommended that you not try synthetic oil until you have an engine (or new car) with relatively virgin gaskets and seals that will be able to acclimate much more easily to the chemical changes of the newer type of oil.
From: http://searchwarp.com/swa7388.htm

ORIGINAL: GrayGhost01GT

Thanks guys What is the Best Syntheic Oil for my car now I just used Motorcraft 5-20 Should I stay with that ?

ORIGINAL: nanaki

i run motorcraft 5w20 synthetic. it's what ford recommends and it's a lot cheaper than mobil1.

when i got my supercharger installed, the place put regular oil in and my car was acting funny. it wasn't turning over like it should. it'd crank for awhile before actually starting. got synthetic back in, and it pretty much went away. my car thirsts for the synthetic.

ORIGINAL: sandcracker21

once you put synthetic in you car, theres really no going back

I use Mobil One Synthetic, which in my opinion is the best oil for my car. But Keep in mind that once you start with an oil you should stick with it. It's ok to swich brands, just not every oil change.