I live right between San Diego and Los Angeles. If you are planning to check-in 3 hours before your flight, I would say leave no later than 10:00 am. It will be a 2 hour drive minimum. You need to deal with the rental car at LAX, gas, etc, then take their shuttle to the airport. That could take you an hour.
That puts you at the terminal around 1:00 pm. So. Cal traffic stops to look at a cup in the road, so why get stressed out trying to make an international flight? Hope this helps...