Engine oil

Hi, I own a 96 Lincoln continental (120k miles), manual says I need to use Ford Motorcraft synthetic blend oil or engine oils that meets Ford specification ESE M2C153E and of vicosity 5w30. And never to use oils labelle API SA, SB...SG. Now,
1. Can I use fully synthetic oils of 5w30?
2. Can I use oils like Valvoline/ Mobil/ Castrol or they don't meet these requirements?
3. Can I use regular conventional oil? no synthetic or synthetic blend.
4. Can I switch between synthetic & conventional back and forth?
5. I drive about 6 mils evreyday, how often do I need to change oil & oil filter? Would it change if I drive 100miles a day?
6. Does using a 5w20 or lesser viscosity oil increase mileage but provide the same protection to the engine? I live in Atlanta GA fyi.

Thanks,

Hi,
First all you should need to do it put in 5w30, You can also put in Synthetic, but I do not waste the money. Just make sure you put in a good quality oil like Castrol, Quaker State, etc. What I am saying is don't put in the Advanced Auto or Auto Zone brand, even though it is probably OK, stick with the brand names.

Synthetic is suppose to be compatible with regular motor oil, so you can switch back and forth.

If you go only 6 miles a day I would change it every 6 months or so. If you drive 100 miles a day that is 3000 miles in 30 days. I would then change it at the 3000 - 4000 mile interval.


Steve