All the above posts are true. However, I own a 99 Accord with the 2.3 VTEC and I have stayed with 5w-30. Although 5w-20 has indeed shown really good results in engines that specify 5w-20(I'm not a 5w-20 basher - I use it in my 2003 Accord), the original manufacturer's recommendation was for 5w-30 year 'round and 10w-30 if the temp remains above 20 degree F. The good news is Valvoline synthetic is available in 5w-30 and, at least around here, is sometimes up to $1.00 a quart less expensive than Mobil 1. FYI, I currently have Mobil 7500 5w-30 in the engine ($2.08 a quart at Wally World - the Mobil 1 is $5.19) - the few UOAs I've seen look really good. I also have a moderately large stash of Philips Trop Arctic synthetic blend (still available at Wally World for $1.24 a quart), both 5w-30 and 10w-30 and I will start to use this when the Accord is due for a change. Just my 2 cents. Good luck.