Rick's b.log - entry 2020/02/04

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Aixam 400 fuel efficiency

Yeah. I'm new to this driving thing. Instead of trying to work out my routes, why not just take photos of that thing on the dashboard that records the distance travelled? Duh.

So I did. Here is the 18th of January, after having filled up, when the counter is at 369.9km (let's just say 370).

I next filled up nine days later on the 27th of January (that's 8h35 in the morning), when the tank was supposedly a little over a quarter full and I had done 639.9kms (let's call that 640).

That fill was 8.84 litres and cost €12,46 (€1,409/litre).

The next fill was this evening (4th February, again nine days), when my tank was between a quarter and half full and I had travelled 882.8kms (we'll consider that to be 883).

And with a cheaper price of €1,369/litre, it was 7.70 litres which cost me €10,54.

Okay, the first observation is that I don't appear to have a 16 litre tank. It looks that either the level sensor is horribly wrong or it's about 12 litres. Which is actually pretty tiny (consider a six pack of 2 litre bottled water - it's that much!).

However, the first fill (meter a little over quarter) took me 270km, while the second fill (meter between quarter and half) took me 243km.
Therefore, as a "rule of thumb" I should expect to get about 100km per quarter of the tank, with an autonomy of around 400km; which is what I was expecting. But note that trying to actually do 400km does mean risking running dry.
Having said that, if I should feel so inclined to want to drive to Clisson, it's 100km there and 100km back so perfectly possible to do that from a fill and not have to panic over running out. I can't really imagine wanting to go much further as that'd be around five hours of driving! My concentration struggles with five minutes. To do five hours would need a lot of tea and mental TLC afterwards.

When it comes to working out a cost, it is difficult as petrol prices are more volatile than bitcoin. So what I'm going to do is take the total distance (513km) and the total cost (exactly €23) and tell you that it costs €0,0448 per litre. The reason I give it to that degree of precision is because it is more useful to think of the cost per 100km. To do that, just move the decimal point two places to the right, therefore...

Not bad for a dinky little two cylinder diesel engine in a tiny car that was made when Acorn was a thing.

Speaking of mental TLC...

It's a shame that it is only between 1pm and 3pm on Tuesdays. I'd probably prefer it when it wasn't so bright and noisy.

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David Pilling, 6th February 2020, 02:28

From the shoppers point of view, lots of light and no noise is optimal. Seemingly they play music to make it harder for people to think.    My car has computer, firmly stuck at average speed of 30 and average miles per gallon of 40.    Fuel meters have never been linear. There is good reason for there to be a little fuel left after the meter shows zero. Just like speedometers read a little less than the true speed.    Driving gets easier as more of it is offloaded to the subconscious. It is hard mental work at first when you're thinking about every action.    UK has just decided to scrap petrol/diesel cars 5 years early - panic has now set in - quelle surprise.

Rob, 6th February 2020, 14:00

I had a car once (company Passatt) that had a fuel level meter that constantly read high. I actually ran out of petrol a couple of times when the needle had only just hit the red line at about the 10% mark. So your 1/4 full tank may not be anything near that, high or low, and until you run it dry you'll never know if you have more or less fuel than you think you do, and thus the actual capacity. Not something I'd recommend doing, btw.. the accumulation of sludge at the bottom of the tank is never a healthy thing to try running through the engine!

VinceH, 7th February 2020, 12:00

My car's computer tells me my average speed is about 19mph, and my average mpg is just over 40.    I also run an app called "Mileage"[1] on my phone, and punch in the relevant figures whenever I fill up. That reports an average 40.06mpg, and an average cost/mile of 14p, which would be 8.75p/km, so £8.75 for 100 of them.    My previous car (which died the day after I returned from Wakefield last year) was giving me around 36/mpg on average.    [1] Recommended.

Rick, 7th February 2020, 21:37

David - I wonder how your car's computer managed to record 30 as the average? Unless the firmware is doing something REALLY silly like counting all the time when the dashboard is 'active' but the car isn't actually moving, like "at a traffic light" or "waiting in a car park" as "moving at 0 mph"?    I tried to work out the accuracy of my speedometer from the "this is your speed" thingies that are cropping up all around (it says "Merci" if you are driving at <50, or a bright flashing red GRRR! face (or other warning) if you're going too fast). I *think* that when the speedo says the bar after 45 (so 47.5), I'm actually doing 45. I can't be entirely sure as all those gizmos say different things! There's one that tells me I'm doing 39 when my speedometer reads just shy of 50. Yeah, right.    It's all very well to claim to scrap dead-dinosaur vehicles (France, I think, wants it done by 2040) in order to appear to be doing something "green", but the pertinent question is - replace them with what? Battery technology isn't really up to it. One thing that would put me off a battery Sans Permis (other than the stupidly-high cost) is that they manage about 50km. So I could get to work and back no problem. I could NOT get to Châteaubriant and back, and anywhere further afield? Forget it. Plus, there's the question of all the nasty stuff in the battery and in the creation of the battery cells, not to mention the fact that dead dinosaurs are still being toasted, just it's happening in a power station far away rather than under the bonnet. So is it really the big green solution that it pretends to be?    Rob - I wonder if mom had something like that happen to her once? She was a "fill it when it reaches half" person (a habit I'm continuing) and she would get really stressy if it edged towards quarter. I don't think I saw the little "fuel low" light EVER on any car she drove.    As for the sludge, I'm aware of that and I dread to think what's kicking around in the bottom of a 23 year old tank. However, having said that... shouldn't the fuel intake suck from the bottom of the tank?    I've noticed that my fuel meter reads low when I first start the car (battery 12.6V) to provide a more correct reading (correct as in saying it's full when it is) when the car is running at driving speeds (battery 14.3V). That's not all. If I go around a bend sharply (I wanted to right "at speed" but I realised that 30kph probably isn't) or over a speed hump, the guage swings left and right as the fuel sloshes in the tank. Felicity is...quirky.    Vince - to finish your calculation, £8.75 for 100km is (according to Google) about €10.30 / 100km.    There are 4.546 litres in a (British) gallon, which to compare with Felicity, would be ~64.4km per 4.546 litres. My tank OUGHT to give me 400km (or thereabout). Your engine in my car? Would be comical,but not so practical. It'd manage 170km.

Rick, 7th February 2020, 21:41

"right" -> "write"  "guage" -> "gauge"    Yup. Time to hang up my keyboard and hit the sack. It's been a long week...

David Pilling, 8th February 2020, 13:42

Rick - I had not thought about the average speed - now you mention it, there has to be a definition of not travelling to edit the calculation, or else the average speed would be close to zero (since it spends most of its time parked). I don't know but I would guess when the engine is running is when it starts computing the average. The joke is being so firmly stuck at 30 mph, given quite a lot of travel on supposedly high speed roads. In other words often I am going a lot slower than 30 mph.

Rick, 8th February 2020, 14:20

I went somewhere new today, used Google navigation so I didn't get lost (I felt I knew the way, but not well enough to do it blind).  There's a little speed indicator at the bottom left.  That's useful, I thought, I wonder if I can find an app that does that?  Well, there are a few GPS speedometer apps. I picked two that didn't have onerous permissions, and watched in amusement as I slowly travelled a kilometre while parked and eating a Big Mac. I know that GPS, when it has a good fix, has an accuracy of about six metres. But wouldn't it be best to hold off on reporting anything until out of the zone of accuracy (six metres isn't much, even at 10kph)? Because if the alternative is to take all the inherent wobble and add it together and try to pass it off as distance? Yeah. No, *I* didn't move, reality (mathematics) did.

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