I would not rely on the trip mileage indicator.

Record the miles on the odo at fill and then the same at next fill.

I'd maybe record the miles on trip and odo at same time to see if they are in synch.

93 octane will hep a bit but not 20% more.

2 years ago on way to Concorso I stopped at a Union 76 in San Juan Batista off 101 for gas. They had 92 octane (very rare here). It was a noticeable difference in performance but I don't recall any outstanding mileage difference.

 

The 360 has a 25.1gal tank.

You filled up only 19.7gal. First off you were not even close to empty or else you didnt even come close to filling it up.

Second off you calculated WRONG.

You could have burnt 23gal of fuel and then only put 19.7 before the pump stopped. If you didnt top it off then it varies as to how much you put in. Because of this you think you burned 19.7gal in the 473 miles you went and calculated 24 mpg. In reality it could be as low as 18mpg.

Dont rely on what you just put in the car to figure your mileage especially if your not topping off. Figure if you are really low you have ~2gal left probably, so 23gal have been burnt. So 473/23 = 20.5mpg. Still pretty good unless you do ALOT of highway cruising.

 

24.7 according to the manual on page 6.12.

Good point and again the owner's manual lists, on page 6.4, mileage for the manual tranny as 11.8 city and 20.3 hwy.

 

maybe it was a very long down hill.

 

Maybe Dave's "over the hill"!!!!

 

I'm tempted to believe this is true only so I can convince myself that buying a Ferrari is a good idea.

 

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I love how the biggest problem with the car is that its getting TOO GOOD of MPG... lol. Its just kind of ironically funny is all!

 

No, the automatic shut off does NOT happen at the same place everytime. In fact it is usually WAY off day in and day out. I ALWAYS top off my cars. Sometimes I can add as much as 4 gal more other times only 2. Fuel likes to bubble and foam up, if you pump very very slowly then yes the auto shut off would probably be pretty close, but other than that it can go off really early when you still have a lot of room left in the tank.

2 fillups ago you may have gotten 23 gallons(total) into your tank before the shut off. This time only 19.8. You think that you only burned 19.8 but could have burned up to just shy of the 23 gallons. the auto shut off is NOT a reliable device. After your last fill up you may have anywhere between 20-25 gallons in your tank. If you burn THE full amount and run out of fuel, then only fill up to 20 gallons you WOULD not have gone the milage indicated on 20 gallons. You would have gone the indicated milage at 25 gallons. That would be a phantom 5 gallons you would have thought you had making your mpg much higher. Hence the wrong calculation.

 

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But did you always go to the same gas station and filled up on the same exact pump?

 

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Hahaha, 24gpm? no way, that's the same as my hatchy.

 

dave,
just been glancing over this thread but the other posters are correct about the inaccuracies of your calculations based on the criteria you used for measuring the variables. you are saying they are splitting hairs but you are using hugely rough measurements, from a one time calculation to present a figure as accurate and scientific. id always sit much happier in the splitting hairs camp on that one though maybe its my engineering background.

saying that you always fill up as soon as the red light comes on and always fill up to auto shut off doesnt mean that these events happen at exactly the same fuel levels each time. theres so many variables that add potential to change the result that it cant be considered accurate in the least. the only one finite value is that you cant use more fuel than the tank capacity but even that is less than clear cut since theres issues with expansion both of tank and fuel and evaporation.
the potential for variance is huge and the values involved mean a small change can impact the result significantly.

the more times you do this though and average out the results, the closer you should get to an accurate average mpg figure however so if you are interested in what your car gets then keep looking at it and you should start to see a trend appearing.
regardless its impressive that its not way down towards the 12mpg figure thats for sure.

nice to hear you are enjoying your 360 though and getting out and about in in plenty. too many people coddle them. i was hugely disappointed by the 360 and almost tried to get the 355 back before deciding it had run its course and my reasons for wanting to move on from that car had been sound.
thankfully they got it back with the 430.