I have been using Pennzoil 10W-30 synthetic (about $7.25 per quart) with Mobil M1-104 oil filter simply because they don't sell Mobil 10W-30 (100% synthetic) in Korea. However, after finding out that this particular Pennzoil belongs to Group III, I decide to try different product. This product I am now considering is produced by SK Corporation (www.skzic.com, English available but this product isn't available in English yet) and is available in 1-liter 5W-40 100% synthetic for $3.20. It advertises the following: *Excellent engine protection in extremely high & low temperatures *Remarkable anti-wear properties *Outstanding fuel economy *Exceeds all major car brand requirements of API SL, ACEA A3/B3/BR, BENZ, VW 502, 505. All my cars came with 10W-30 oil from the factory. Please tell me how 5W-40 will effect the engine performance and protection, fuel economy, etc. Please comment on this oil too. Thanks in advance.