Toyota 2008 Prius Quick Reference Manual page 395

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.
368
PRIUS_U_(L/O_0802)
SAE 5W-30 is the best choice for
good fuel economy, and good
starting in cold weather.
*
: If SAE 5W-30 oil is not avail-
able, SAE 10W-30 oil may be
used. However, it should be
replaced with SAE 5W-30 at the
next oil change.