I am not sure what you mean. Or what are your real concerns or issues. You can continue to use the GF-3 oils. Or you can use the GF-4 oils, which are backwards compatible. Seems to me you have a buying opportunity if they are putting the GF-3 stocks on sale to make way for the GF4 stocks. Both GF3/4 come in 5w30. I would continue to use 5w30 if that is what the OM on the Corolla recommends.
I considered a Toyota Corolla vs a Honda Civic. All my reseach indicated that Mobil One in the recommended viscosity is probably one of the best. I went with the Civic and the Civic's recommended oil change interval is 10,000 miles normal/5,000 severe.(OM recommends 5w20, if it matters, FYI) After the meager warranty I would have no concerns about going to a 15,000 to 20,000 mile interval with Mobil One 0w20-5w20.
There is literally a plethora of good to GREAT conventional oils. Mobil, Chevron, EM etc etc. Some UOA's OCI indicated that the Exxon Mobil Superflo 5w20 still has plenty of TBN left at 9100 miles!!!! So I truly don't know why you would change at the 3,000 mile OCI.
[ February 25, 2005, 04:34 PM: Message edited by: ruking77 ]