You need 5W-30. The oil viscosity recommendation should be marked on your oil cap and in the owner's manual.
Cheers
For a 1999 Solara v6, the oil capacity is 5 qts. of 5W30.
STP's part number is S3614. This oil filter fits a 2006 Toyota Solara (6 cyl) and other similar years of Toyota.
5,000 miles
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5w-30e
The oil pump is in the oil pan (aka the "sump").
5w20
5 qt
Gonna need to be a little more specific, but I can tell you it does take 5w30 oil.
3000 miles is safest
As you listed no year I cannot tell you what it is supposed to use. All, I can tell you is to use exactly what Toyota recommends and nothing else. And I would also ask you the question, Why Not put 5w20 in your Toyota Solara if that is what Toyota recommends?
See answers already posted to "How do you change oil on a 2004 Toyota Solara," "How do you change oil on a 2006 Toyota Solara," "How do you change oil on a 2007 Solara." They're the same as the '08. The short answer is, oil changes are the same on almost all vehicles. 1. Place a suitable container (5 quarts or more for the Solara) under the car. 2. Remove the drain plug and let the oil empty into it. 3. Replace the drain plug and move the container until it's under the filter 4. Spin the filter off (in the case of the Solara it's wise to place rags or paper towels under the filter to prevent a mess on the floor) 5. Replace filter 6. Add five quarts of oil 7. Start engine, check for leaks 8. Reset maintenance light. Cheers