Re: SYN oil
I've used Mobil 1 in various vehicles since it was introduced.......I'm using it in my 99 TJ now. I've looked at Amsoil's specs and they appear impressive......my only objection to them is the limited distribution and usually high cost. Mobil 1 on the other hand is available everywhere for a little more than half the price of Amsoil. Most synthetics exceed the performance of any parafin (did I spell that right?) based petro oils just by their broad temperature range of stability ...... you can take a quart of Mobil1 0-W-30 and a quart of ANY parafin based petro oil and put it in the freezer over night ......in the morning Mobil 1 will pour and the other will be gell .....take the same two quarts and put them in pyrex and put them in an oven at over 500 degrees (600+ actually) and the parafin based oil will smoke and eventually turn to asphalt and the Mobil 1 will still be a motor oil......no contest.
If you go to Mobil's site they list the features of each syn oil they sell and what features each have. 5W-30 has the best fuel economy 0W-30 has the best thermal stability etc. With the right weight synthetic you'll never stall on cold start up for lack of oil flow as you do with conventional motor oils. Some like to use 20W-50 for reasons that evade me ...... perhaps it's the misconception that anything for racing is superior for any application .... even in a synthetic I wouldn't use this unless I had a turbo or a true extreme stress performance application .... or perhaps lived in Death Valley.
Oddly enough ..... and this really sounds strange ....an natural product ...Jojjoba bean oil (now I know I didn't spell that right but I think that it's pronounced Hohoba) is superior to most motor oils, including synthetics, in most specifications including flash point - it is hopelessly expensive though.
I've used synthetics on most of my vehicles since '75 ..... one, a Citation w/ 2.8 V6, spun the odometer twice plus 50K before it was given away (the dash, head liner, and interior were trashed) that one was maintained to Mobil's recommended specs (25k or 1 year with filter changes at the normal recommended drain intervals) it was still quiet at a quarter mil.
With that kind of performance ..... how can I go with anything else?
I'd recommend Mobil 5W-30 or 0W-30 ........ that's just my opinion ...... and ...... just like a&^%%holes....everyone has one.