Originally Posted By: Garak
Originally Posted By: SR5
My GM owners manual says to use either 10W-30 or 15W-40 in either A3/B3 or A3/B4. That's it.
GM, at least at one time, would warn regularly against 10w-40, probably because some of them were so poor years ago, with a lower HTHS limit and so forth. Did such warnings ever appear in GMs down under? Now, of course, the 10w-40 options should be much better, but they're still obviously not an option in a North American GM manual.
No mention of 10W-40 in the owners manual, positive or negative.
I would never use an old school 10W-40 mineral oil with it's heavy VII load, but I have never seen one for sale on the shelves, so it's a moot point. Most of the 10W-40 oils for sale here are name brand semi-synthetics, with A3/B4 spec. I have no problem using that in my car.
I only know of two full synthetics 10W-40s here, Nulon and STP, which are both second tier brands IMO.
My focus has recently shifted to 30 grade oils, but at $20 for 5L of Shell Helix 10W-40 A3/B4, I had to grab some....they were almost giving it away.