Toyota Avalon 2008 Quick Reference Manual page 334

4-3. Do-it-yourself maintenance
Recommended viscosity
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Outside temperature
How to read oil container labels
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The ILSAC (International Lubricant Standardization and Approval
Committee) Certification Mark is added to some oil containers to
help you select the oil you should use.
310
SAE 5W-30 is the best choice for
good fuel economy, and good
starting in cold weather.
If SAE 5W-30 oil is not available,
SAE 10W-30 oil may be used.
However, it should be replaced
with SAE 5W-30 oil at the next oil
change.