My numbers are very similar but reversed "Winter"/Summer.
Gary....on one of your other posts I read about gasoline all coming from the same place and additives being the only difference. I have said this for decades. Some people in the past thought that various oil companies had their own storage tanks etc. It was a good point that you made. We still don't really know what additives any particular delivery actually uses though. I'm on the east coast of FL...where are you?
I get right around 37 mpg during the summer months and 39 to 41 mpg during our FL "winter". I'm convinced that the lack of hills where we live makes a consumption difference. How about you?
I'm near the West Coast by Spring Hill, FL. Mileage questions: I get about 32, I think. Car only has 650 miles thus far. I haven't driven too much cuz of medical issues, but that will change. Doubt that my '23 Tucson SEL 2.5 could make much more as I do too many cold starts and really short trips. That always drags the mileage down. But she's capable of doing over 40 every day if I drive far enough.
Well, we do know a little about additives. We know that Chevron uses Techron, and also sells it by the same name in a very similar formulation at the local auto store. We also know that Techron, like other formulations from other gas companies, is not just one chemical, but rather a cocktail of many additives each designed to do different things. But the most important one to most of us is the detergent portion of the mixture. As you probably figured out, I have researching in my blood. As an English teacher, I spent a fair amount of energy teaching my students just how to do research, how to write papers, and how to find and utilize iron-clad evidence in their writing. Here I am retired, and now I do for fun what I once did for a paycheck. I enjoy researching: but as we all know, every gas company is very tight lipped about their formulations. Specifics are nearly impossible to come by. For example, Shell uses what they call V Power Nitro in their premium only, but uses a slightly lesser amount of much the same stuff in their lower grade fuels. They say it has nitrogen in it and more than one researcher has confirmed this. What is it exactly? Who knows. Of course since they are indeed top tier certified for all grades, all their fuel still meet TT mandates, it's just that their premium contains MORE still. That has led some to proclaim that ONLY their premium is top tier. WRONG. Gotta be careful WHERE ya get yer information.
Back to just what's in each fuel. Likely we'll never know. I read a post written on a car forum last week. The poster said he drove a truck delivering gas to perhaps 5 different stations, and could readily quote the name and exact amount of the additives he put in the fuel at each different station. But he quoted names like Techron and V Power and such. His post was something like 9 years old so it wasn't really relevant info anyway, but even with that knowledge, we don't really know what's IN these formulations. But he did say that the cheaper companies use additives, (minimum federal requirements only) and buy it from the lowest bidder on the open market, sometimes changing "brands" daily pending the price and availability. Top tier retailers of course don't do this. Their fuel is monitored for content BY THE TOP TIER ORGANIZATION. But even between top tier suppliers, I find it nearly impossible to determine which is best. For example when AAA did their huge comparison (and provided the research results) on this subject several years ago, they tested several cheap stations and several top tier stations. The differences were astonishing. The cheaper stations were clumped at the bottom, and the TT stations were clumped at the top, and there was a huge margin in between. But there was a slight difference between the individual TT stations. It's just that AAA wouldn't divulge which was which. UGGGH.
Obviously, there's a reason for this, gas companies protect their secret formula and proclaim it the best. As far as I can tell nobody knows for sure. I've researched this for probably 7 years... on and off. But what I have found is that Chevron and Shell seem to come out on top with those who seem to know. I've read this a number of times. These are only opinions however: like I said, who knows? But we do know that either one is a good choice and that's good enough for me.