hello, I have two y-block powered cars, a 312 and a 239. the books state when changing the oil w/ filter you should add 6 qts, both cars have identical dipsticks and I have no reason to believe the dipsticks are not original to these engines. If I add the recommended 6 qts., both engines read considerably over filled. if I add 5 qts., its dead on the full mark. both engines have spin-on filters. could ford have been this far off on calibrating the dipstick? has anyone else experienced this? also I am going to open this can of worms, I have had the 312 for over 20 years and have always used Castrol 10w30 with never any problems, I use it I both cars, any thoughts or opinions on type of oil to use? thanks, doug.