My best friend swears up and down that occasional fillups with mid-grade gasoline keeps his mileage up. He claims the midgrade stuff has detergents or something which keep deposits out.
I call BS on this one- he can’t prove the better gasoline is actually giving him better mileage, because his driving isn’t consistent enough to attribute occasional fillups with midgrade gasoline with improved gas mileage.
Is there any legitimacy to this?
Also, my friend claims that his 1996 Jeep Grand Cherokee can only run properly on certain brands of gasoline. I thought most companies get the gasoline from the same refinery(ies), which would mean the only difference is how much you pay for it. But he claims that putting anything other than Chevron or Shell in his tank will cause the engine to sputter and lots of hesitation when accelerating. Is there any truth to this as well?
The difference between regular, supreme, and super-duper is octane. Engines with higher compression ratios need higher octane gas to prevent knocking. Higher octane grades are not “better” gasoline, and if your engine doesn’t knock it’s a waste of money to use a higher grade than recommended by the manufacturer. It will not increase fuel economy. I’ll bet you can confirm this all over the web by searching on something like “gasoline octane grades knocking” or something like that.
As far as brands, there are detergent additives and so forth that different oil companies use to try to differentiate their brands. There probably isn’t any difference in additives between grades, but I don’t know that for a fact. But these additives generally affect engine maintenance and engine life more so than performance, so I would be very surprised if one brand of gas made your friend’s Jeep run well and another brand made it hesitate, if both brands were the same octane.
It’s possible your friend’s engine is mildly out of tune, and the higher octane of mid-grade gas is helping to hide problems he might be having.
It’s true that different brands of gas have different detergent additives, but I don’t know if the different grades of gas within the same brand also have different detergents. In either case, you can go to any auto parts store, and even many discount stores, and pick up a little bottle of detergent additive for less than the difference between a tank full of regular and mid-grade. Just pour it in the next time you fill your tank and you’ll get whatever benefits there are.