As the current owner of 2 1987 4Runners with the 22RE I suppose the term "Old 4Runner" is relative lol. For how you use it I'd also get some of the Napa Synthetic on sale right now. You could get 10 quarts for $30 right now combine it with the leftover T6 you already have to make 2 oil changes. I've owned a 2002 and 2003 Tacoma with the same engine you have, the 2002 was supercharged. Neither one seemed to ever be picky about oil. The 2002 with the supercharger even at 150.000 supercharged miles returned beautiful UOA even on 5w30. I really don't think you need a 40wt oil in that engine. If it was me I'd probably just pick up a 5w30 in the Napa Sunthetic and drive on happily at 7,500 mile OCI or more without a second thought.
As to the change in oil weight causing a significant change in fuel consumption. I have about 60,000 miles of gas and maintenance records for one of my 1987 4Runners with the 22RE and I can show that without a doubt using heavier oil (40 vs 30) costs me about 2 MPG across the board (city, mixed, highway) in fuel economy. On Xw30 it gets 17.8 city and 20-21 Highway, switch it out to Xw40 like it has in it right now and it drops to 15-16.2 city and 17.8-18.2 highway. It's repeatable data spread over 5 years and about 60,000 miles across all seasons that immediately shows improvement back to the higher MPG as soon as it's filled with 30wt again.
As to the change in oil weight causing a significant change in fuel consumption. I have about 60,000 miles of gas and maintenance records for one of my 1987 4Runners with the 22RE and I can show that without a doubt using heavier oil (40 vs 30) costs me about 2 MPG across the board (city, mixed, highway) in fuel economy. On Xw30 it gets 17.8 city and 20-21 Highway, switch it out to Xw40 like it has in it right now and it drops to 15-16.2 city and 17.8-18.2 highway. It's repeatable data spread over 5 years and about 60,000 miles across all seasons that immediately shows improvement back to the higher MPG as soon as it's filled with 30wt again.
