We'll Im a going to go to syn. I get most of what I can from Wally'*, wife works in warehouse so we get a small discount as well. I only use AC Delco filters though so they come from Advance.

Question what weight ? I always used Castrol GTX 10-30. I see I can get Castrol synthetic in 10-30. I see Mobile 1 is 5-30. I'd like to hear some opinions and also about 5-30. Being old school and having heavy equip (15-40) even 10-30 made me cringe alittle but I understand the principles. 5-30 sounds nuts. Educate me

hi

if going to a real synthetic like M1 or Amsoil, ( their a group IV rather than the lesser grp lll which the others are) you might wish to use a cleaner like Neutra or auto-rx first before making the switch.

once that is done, i'd recommend the M1 10w-30 as it has proven itself in many uoa with the 3800 engine. the 10w-30 seems to have a more stable TBN over the 5w variety and seems to resist thickening especially at longer change intervals..

I use Mobil 1 10W-30 in the summer, 5W-30 in the winter, the weights recommended by GM.

Mobil 1 is aviailable in 0W-30, 0W-, 5W-30, 10W-30 and 15W-30.

The number on the left shows how the oil flows when it'* cold, the number on the right, when it'* hot. I wouldn't worry too much about running a synth 5W-30 year round, in fact, that'* what I do in our other car (again, factory recommendations).

However, some of the newer recommendations are for 5W-20. To me, that'* crazy. They are using a thinner oil to get the last bit of EPA fuel mileage that they can. Seems like there'* a compromise with durability there.

Anyways, the 5W-30 should be fine in synth.

hi


for M1, which is one of few group IV synthetics , i would suggest 10w-30 over the 5w-30 year around regardless of what your manual calls for, as its tbn is much more stable.

another oil worthy of consideration due to its price and additive package is the Rotella T 5w-40.