I don't know if this was hashed out here yet.I just did my summertime oil change.My 4.0L Jeep engine uses 5.7 litres in the sump...so I put in 4 litres of 10W-30 and 1.7 liters of 15W-50 Mobil oil with SuperSyn..what ever that is...what viscosity I have who knows..11W-38 sounds good to me
...anywho...what is the SuperSyn additive in the new Mobil oil...their web page says the 15W-50 has a little extra SuperSyn than the other grades..by the way my idle oil pressure in drive (hot) is up a tad...and the notorious piston slap with these motors is almost non-existant now