Hyundai is Kia's parent company, now. I have a 2003 Hyundai Sonata with the 2.7 liter V6, and the owner's manual lists 90 degrees F. as the upper limit for using 10W-30. I asked the dealer's service manager for clarification. His answer was that they use 10W-30 Quaker State in customers' cars year round in inland southern California with Hyundai USA's blessing despite what the Korean printed manual says. We see two or three weeks in July and August in excess of 100 degrees, and last week had three days nearly into the 100s. More of the same expected by the middle of next week if the local weather jerks are right. (I picked the wrong occupation. Other than politics, what other profession pays so well for being so wrong than reading a prepared script of the weather forecast on local TV stations?...) My '91 Sonata's old Mitsubishi-based V6 owner's manual said the same thing - apparently Hyundai Korea is a bit slow to upgrade their recommendations. I put 90,000+ miles on it in five years before I traded it in disgust for a 96 Accord. (Couldn't keep juice in the A/C and no one could figure out why.) It never leaked or used 10W-30 oil in all that time, though, and the engine was still strong and sounded good - cold or hot. My 2003 Hyundai Sonata manual still recommends use of SG and SH oils, too, identical to the 1991 manual. The viscosity spread of a 10W-30 oil is 20 pts, but 30 pts and 40 pts respectively for a 10W-40 or 10W-50 oil in hot weather operation with conventional dino oils (Group-II or Group-II+). If you feel you must take extra precaution in extreme heat, I'd suggest 15W-40 heavy duty fleet oil, if conventional, or going to full synthetic with its inherently higher viscosity index base oil. I plan to continue with 10W-30 in my car, though.
[ May 25, 2003, 03:35 AM: Message edited by: Ray H ]