What oil to use for my 1988 V6 Pontiac Fiero?

[lilkhmerraider]

This is really about which numbers are best. I usually use Fully Synthetic but I want to know which number oil would be best. The number on the cap to the engine says 5W-30. The previous owner used 10w-40. Can I use 10w-30 as well? I live in Southern California and its pretty warm out here. Which oil should I use?

 

[Marble]

Use the recommended 5-30 for now. If you notice any smoke coming out of the exhaust, switch up to 10-30 the next time you change the oil.

 

[Oreif]

How many miles on the engine?

Personally I would use 10W-30 for synthetic or 10W-40 for regular oil. I don't like using 5W oils on older engines with +70K mileage.