Ford Repair: Mobil 1 Synthetic, cream puff, grand marquis

Question
Hi Steve. I have a cream puff 92 Grand Marquis for my retired wife. 62K orig. miles. Owned since new.I do own oil changes etc.Wife only averages 500 miles a month around home in Florida.Question:
Would you recommend I go by miles now with this top SYNTHETIC or time? Engine stays clean between changes. Since you,r into serious engines, what do you think about MOBIL 1???
            Thanks,   Ken  

Answer
Ken-

  Honestly, I think Mobil 1 synthetic is the best readily available oil you can get.  There are some specialty blends that are a bit better like Amsoil or Royal Purple but Amsoil requires you to go through a distributor (i.e. not available in 99% of parts stores) and even if you can get it Amsoil, much like Royal Purple (which is mail order accessible) can run you $6 or $7 per quart.  As far as how long to wait, with 10W30 I'd say you should be good for 4000 miles or 5 or 6 months.  You could probably go longer (especially with a 10W40, but I don't recommend oil that thick in a car that doesn't see heavy-duty driving) , but if it were my car I honestly wouldn't be comfortable with that.  Hope this helps.

Steve