the past couple years ive always done 5w20 during all months except summer where i switch to 10w30 because of the heat. it will get around 102+ regularly. based on teh manual it says to use 10w30 when its that hot and im wondering if thats really neccessary? im using synthetic oil so that should stand up to the heat better than normal 5w20 oil. instead of 10w30 should i maybe use 5w30??

what do you guys think? i know the 10w30 gives a decreae in MPG as well. keep in the mind i drive teh car faily hard and have quite a few mods (pushing the 300whp barrier) so my engine probably gets a little warmer than normal.