I've been running the same (Valvoline SynPower 5w30 motor oil) in my IS250 for the past year (only have had it for a little over a year now) and had previously run the same in my ES for 4-5 years. I never noticed anything bad with it, in fact I felt that the car starts and runs smoother with full syn vs standard motor oil (noticably well in the brutal Minnesota winters). I still change the oil every 5k even though full synthetic can probably go for longer time frames.
I use Mobil 1 5W30 Full Synthetic, a lot of others on the forum seem to be using it too. I haven't had any issues with it, previous owner had been using it too so i can't say i've felt a difference or anything, but car always runs nice and smooth!
07 IS250 - SOLD
08 Altima Hybrid
98 Prelude - SOLD
^ TSIB below. They don't say it, but the reason for the TSIB is because 5w20 gives you slightly better gas mileage vs. 5w30, at the cost of slightly less protection after your engine is fully warmed up. If you're stop light drag racing on a daily basis, you'd be better off with 5w30, but it's not that big of a deal.
^Interesting. I'm currently using Royal Purple 5W 30. Can anyone confirm if 5W20 provides better fuel mileage?
It's thinner when the engine is at operating temperature. That will give you slightly better MPG's and slightly worse protection. Car companies recommend the thinner oil to boost the fleet MPG's for the government. The same company will recommend the thicker oil for the rest of the world...
You're choice - it's more important to change the oil when recommended than the weight.
BobISF- F for fun, fast and fenomenal.