Like a rock, Their two factions in the oil viscosity world. New Age thiner viscosity nuts and Old School thickest for temp school. I would not use Delvac 1300 15W50 in the winter. I would not hesitate to use a group III,IV, or V synthetic though in 5W40,10W40 or 10W30. Short of anartica you will never see me recomend anything lighter then 10W30 even synthetics. If someone else mention synthetic 5W30's I will conceed that they have been shown to be almost as effective as synthetic 10W30. My Dad runs M1 15W50 year round wich I will not do.The M1 15W50 flows as well as a conventional 10W30 in cold weather. He has yet to have a cold start oil flow problem and he is at 200,000 miles uses no oil and runs like a top. We had to have it apart this year to replace one of the timeing chain tensioners. We live in Michigan so we see some cold weather. I think that the 5W40 Rotella T Synthetic would serve you well.I might also point out that you have 6 months before winter comes! Mobil 1 15W50 has the following propertys:Typical Properties
Mobil 1 15W-50
SAE Grade 15W-50
Viscosity, ASTM D 445
cSt @ 40º C 125
cSt @ 100º C 17.4
Viscosity Index, ASTM D 2270 153
Sulfated Ash, wt%, ASTM D 874 1.3
HTHS Viscosity, mPa·s @ 150ºC ASTM D 4683 5.11
Pour Point, ºC, ASTM D 97 -45
Flash Point, ºC, ASTM D 92 230
Density @15º C kg/l, ASTM D 4052 0.864
Compare that pour point to a conventional 5W30 or 10W30. Also check out the HTHS number!!!! You can get the 15W50 on sale at walmart right now $18.99 for 5 quart container!
[ June 08, 2003, 09:28 PM: Message edited by: JohnBrowning ]