For almost the last two years, my wife has been driving an 07 Toyota Avalon, which to date, has been virtually flawless. After a couple short fills of conventional oils, at ~5k miles, I added the first fill of GC 0w-30. The car’s 3.5L 2GR-FE seemed to like the stuff just fine (runs very nicely, no consumption). At ~10k miles, I changed oil, again using GC. Last weekend, with my wife about to take a big road trip, and having reached 14,500 miles, I changed the oil, this time using Pennzoil Platinum 5w-20. This is a pretty hefty change, going from a 12+ cSt oil, all the way to one that is 8.5 cSt hot.
Yesterday afternoon, she got back from the trip to Atlanta (about 350 miles each way). I eagerly checked the mileage figure on the computer, and almost fell over. It was showing 29.9 mpgs.
This is MUCH better than we’ve ever done on a consistent basis with this car while it was being fed the 12+ cSt GC. On previous long highway runs, 27-ish was about the best we could do (though I’ve tricked the car into higher readings for short runs using some Prius “magic” driving techniques...). GC gives great UOA, no doubt about it, but perhaps it’s just too thick for this car. BTW, the 2GR seems to love the 20 wt PP – it still sounds just as velvety and smooth as it did before. It may be revving a tad more freely, but that’s so subtle it may just be what I’m wanting to hear.
Well, this might just be a happy anomaly, but OTOH, it also looks like a pretty substantial indicator that 5w-20 is the cat’s meow for this car.
Let the debate re-ignite! 
NOTES:
1. Yes, the figures quoted above are all from the car’s mpg computer. I realize that they may be off from the absolute values, but it’s still a valid comparison. I presume that the “actual” numbers would vary in approximately the same proportions.
2. Of course, these observations do NOT count as scientific evidence, and no hard conclusions can be drawn from such limited observations. Still, these numbers are tantalizing, and will motivate to watch this car more closely to see of the apparent gains on 20 wt oil are real or an illusion. I might even consider sharing some of my new stash of PP 0w-20 and see if that makes any additional difference (doubt it, but hey, who knows).
NOTES:
1. Yes, the figures quoted above are all from the car’s mpg computer. I realize that they may be off from the absolute values, but it’s still a valid comparison. I presume that the “actual” numbers would vary in approximately the same proportions.
2. Of course, these observations do NOT count as scientific evidence, and no hard conclusions can be drawn from such limited observations. Still, these numbers are tantalizing, and will motivate to watch this car more closely to see of the apparent gains on 20 wt oil are real or an illusion. I might even consider sharing some of my new stash of PP 0w-20 and see if that makes any additional difference (doubt it, but hey, who knows).
You need to try 0w-10 if you're going to learn the true meaning of the power of the light(er) side of the Force.
see I remembered to use smileys