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6.7 quarts
On the 2008, the manual says 5W30. However, many Lexus dealers use 5W20. I assume this is to try and improve gas mileage slightly.
6.8 quarts
5 quarts 5w30
Buy a battery with the most you can find. The more the better especially if you live in a cold climate.
6.5 quarts of oil
It takes 5w30 and 6 quarts.
5.5 Qts
The 2010 Lexus IS-350 has 24 valves.
The 2010 Lexus IS-F has 32 valves.
The 2010 Lexus IS-250 has 24 valves.
It holds 5.1 quarts.