A boast and an oddity query
 

This is a Honda Type R, with a factory consumption figure of 31mpg.

The weird thing is also the petrol gauge, which you'll see hasn't moved off the very top. The car has a capacity of 50 litres. Usually when I fill up, I get to about 47 litres, then top off with a few additional squirts. On this occasion I got to the usual level, started topping off, and it just went on and on...up to over 54 litres.

This appears to be impossible, and I note again that the fuel indicator is still on maximum - it usually starts to descend after about 50 miles, and as of today it still hasn't moved after 110 miles. Did I somehow tap into a fuel reserve I'd never got to before? I can't explain how I got 54 litres into a 50 litre tank that still had about a gallon remaining.

There may be a vapor reservoir you fill when you run the fuel up to the neck, very similar to my VW. With the valve disabled (a diesel doesn't need a vapor reservoir, there is no vapor), I can squeeze in a gallon more. And yes the gauge is calibrated to the level of the tank, so it will not move until the level drops.

UFO's likely right.

Some Hondas are known to sometimes admit fuel into the evaporative emissions system when attempting to fill the tank's filler neck to the brim.

I used to carry a short piece of 2X4 in my 94 VX. When I pulled to the pump I would lean out of the open door and toss it in front of the left rear wheel. This seemed to help a lot with more consistent fills. Wide and long (under the rear seat) gas tanks that have long filler necks that do not go into the top of the tank are susceptible to incomplete fills. I found that the wifes Nissan Rogue would take 2 additional gallons if I was patient and lifted the wheel well nearest the filler neck. She always had problems getting the tank completely full.
More than the tanks capacity in fuel is not uncommon, but if you try to fill beyond the pumps qutomatic cutoff, to the top of the filler neck, you risk trashing the vapor recovery sytem as well as hurting your mileage.

regards
Mech

I think I must have filled up with magic dust - 130 miles and the fuel indicator still hasn't moved. :D

Reckon I must have tapped into the reserve. But every fill up I've done I've topped off as far as possible, so odd after so long.

Is it possible for the fuel gauge to jam? It's still stuck steadfastly to the top, indicating a full tank after 160 miles. Assuming I did in fact tap into a seven litre reserve, that's about 80 additional miles. It usually starts to fall after about 50 miles, which would make 130 with the reserve filled. But it should have moved by now. I'm wondering if filling up into the reserve (if the case) has jammed something. The computer is properly ticking down the "miles to next fill up" gauge, so that's OK, I shouldn't run out without any warning. But the fuel gauge is weird.

Finally started indicating fuel off maximum after fully 200 miles.

Maybe you're just hypermiling better ;)

On next fill up, I unsuccessfully tried to get back into that fuel reserve I magically found last time. Couldn't. Fuel wouldn't go beyond usual 47 litres or so, try as I might to keep topping off. Consequently, my fuel calculation went off the charts, giving 60 MPG compared to usual 48 or so, impossible but explained by the "short" fill compared to that previous mega one that yielded an additional 100 miles. Weird as hell.

That last time I'd actually just attended a funeral. I wondered at the time if the deceased wasn't playing some mischievous little trick on me, LOL.

I did hear a supposedly true story from years ago, about a man who liked to record his cars' mpg.
He went and bought a new car, and his friends played a joke on him by repeatedly topping up the fuel (in the days when filler caps didn't have locks) for weeks.
After a while they stopped doing that.
And the man called into the dealer and said that his car must have something wrong with it; for the first few weeks he was getting the usual 100mpg but it had recently fallen drastically...