Who All Runs Synthetic In Their 03 Cobra??

5W30 is actually better protection than the 5W20. Ford recommends the 5W20 because it raises their C.A.F.E. rating.

I ran the Ford semi-syn 5W20 for the first 1000 miles and then switched to 5W30 Mobil 1 after that.

U.M.

You can also run 0w20 that Mobil 1 offers. It is made for the Ford and Honda engines that use 5w20. I am switching to that from Royal Purple because it is available in stores here. I am sure that 5w30 is just as good, maybe better because of the higher viscosity when it gets hot, but Ford does my oil changes for free and I try to use what they recommend.

I run 5w30 Mobile 1. Just changed over at 10k.

If you live in the South, run the 5W30. If you live AND drive in sub freezing weather all the time then I would go with the 0W20. Since these cars (03/04 Cobra) run so damn hot I personally feel the 30 weight is much more appropriate.

U.M.

I know alot of guy here in S. Florida with N/A and Blown cars who are real happy with Amsoil 0W20

Mobile One 5w30. Changed at 5000 miles. Used Ford 5w20 prior to switching.

A few facts about oil:
(Most of you probably know this already)

5w20 stands for "5 winter 20"
The "5" is the relative weight of the oil at 70 degrees farenheit, the 20 is the weight at an average operating temp.

any colder than 70 and the "5" gets thicker.
any hotter than normal operating temp and the "20" gets thinner.

0w20,5w20,5w30 all are acceptable on 03 Cobra.

In most conventional oils, the change in "thickness" (multigrade oil) is achieved by adding polymers to the oil. They stay coiled up in the cold to keep the oil thinner (but if it gets too cold, the oil thickens anyway).
When they get hot they "stretch out", and make the oil "thicker"
Over time, the polymers shear (and form deposits) and the viscosity of the oil is compromied.
If you put in a conventional 5w20, it may act like a "3w15" or whatever by the time you drain it.
A larger spread contain more polymers:
For example, a 10w40 would have more polymers than a 10w30...the difference between 40 and 10 is greater than the difference between 30 and 10

Several companies have claimed their synthetic oils achieve a multigrade with no polymers.
This is good if it is true.
Form what I hear, Amsoil, Mobil1 and Royal Purple all claim this on their "low spread" multigrade oils.

Something like 20w50 is NOT acceptable on an 03 Cobra.
That stuff is only good for an old car or a loosely built race engine.
Throw 20w50 in a newer car and see how fast the bearings scuff......they build engines a lot tighter now.