A bit OT: car fuel consumption.

[newshound]

Just filled up the Jazz Hybrid, normally it reports "Range 421 miles" at this point, but today it just offered 385.I wondered if my last tank was the first with E10, so that I'm starting to see the effect of reduced mileage (although the difference is larger than I would have expected). I suppose I could have developed a faulty sensor.

Also, I accidentally pulled up at a "97" pump (the station has been having supply problems with a lot of pumps "not available"), it will be interesting to see if the range improves as it recalibrates itself.

[JNugent]

My experience is that the tank reports varying levels of fullness on different plots of land. The slope under the car seems to be what makes the difference. It also changes as you drive along for that and other reasons.

[Michael Chare]

I would expect the car to use its latest fuel consumption figure to calculate the range. Possibly you were using more fuel than usual just before you refilled. Could the engine have been working harder to charge a battery?

[Dave Plowman (News]

Which filling stations do you know that aren't on level ground?

[Dave Plowman (News]

The new range is generally calculated on the MPG just before you stop to fill up. It should then adjust, according to the use the car gets. 'Miles remaining' on my car goes up after a cold start - as it is calculating on the range you'll get with heavy fuel consumption due to a cold start rich mixture. As the mixture returns to normal the distance left gets greater - most noticeable when the tank is near empty.

I'd be most surprised if you get the same number of miles per tank for every tank.

I've had several cars that say use 97 when possible. Bit of a ritual on a very long journey to use 97 one way, 95 coming back. And never had a conclusive difference in MPG. You'd really need to do it under lab conditions.

[JNugent]

At least two near here, both of which I use. One about a mile away that slopes pretty sharply up from the kerbside (meaning that the nearside of a car being filled is higher than the offside) and one about two miles away - on a hill - where the forecourt reflects that lie of the land and also has a rise from the kerb - ie, it slopes in two directions. The front nearside of the vehicle being filled is higher than the rear offside.

Are there no hills near you?

This sort of thing always affected fuel gauges, even before the advent of trip computers.

[Dave Plowman (News]

So that is the norm for filling stations? On a kerbside? Is this some historic reconstruction village?

Not with filling station forecourts following their contours, no.

[John Rumm]

It might just be a reflection of recent driving style. On mine it can vary quite a bit with its projection on a full tank based on the kind of motoring I have been doing recently. So a fill after a few long trips shows a bigger estimate than one after lots of short round town journeys.

[alan_m]

Since E10 I have done 4 off 250 mile trips, mainly motorway with only 1 pee stop. My consumption is up by approx 7% (mpg down) compared to the same trips in the past. My car reports mpg figures until the trip recorder is reset. I always check the mpg figures for long trips.

[JNugent]

What are you talking about?

They build elaborate terraced structures for filling stations round there, do they?

[The Natural Philosopher]

Only when the floats are not in the tank centre

[newshound]

Not so far as I am aware. The predicted "range per tank" is normally remarkably constant. Sometimes if it has had particularly light use the initial "range guess" is a little higher, but it normally adjusts quite rapidly to a similar figure (i.e. 410 miles after driving ten miles).

[newshound]

Oh I am sure that I don't. BUT, the "full tank" estimate normally varies very little.

[newshound]

Understood. If I'd been thrashing it significantly before filling up that's exactly what I'd have expected, but I hadn't. I'm saving up my line for the unlikely event that I'm stopped for speeding: "But officer, I'm an OAP driving a Honda Jazz, you should be stopping me for driving too slowly".

[newshound]

Interesting, thanks. I looked at the figures for calorific value of petrol and diesel with ethanol and FAME when this green nonsense came in. People may or may not be aware that in the first "tranche" when 5% of all fuel was supposed to be biofuel, in practice the suppliers achieved this by adding 10% to diesel and nothing to petrol (since the volumes consumed are near enough the same, but FAME is cheaper than ethanol).

I assume that now, when you see E5, E7, or E10 on the pump this is more or less accurate (or possibly the upper bound).

FAME = fatty acid methyl esters, the stuff derived from vegetable oils.

[Fredxx]

Theory suggests that changing from E15 to E10 should reduce mpg by

1.5%,on the basis that ethanol has 70% of the energy density of unleaded petrol 24 vs 34 MJ/L.

Given current E5 is often actually free of ethanol, the difference might be nearer 3%.

Any other change can be down to the current low ambient temperatures. Who knows.

[NY]

Can't comment on 95 versus 97 petrol, but I have twice filled up my diesel car with "gold plated" diesel instead of normal diesel - once after passing many garages until I found one that was doing cheaper fuel, but I then went and filled up with the expensive stuff :-(

My perception in both cases is that the engine ran a bit smoother and there was less hesitation when applying power again after coming right off the power to slow down, but that any difference in consumption was lost in the "noise" that I normally see between one tank filling and the next - so no significant improvement.

[Andrew]

Not with Esso Synergy premium petrol. The pump handle says E5 but in most of Southern UK, it has no ethanol at all. All explained on their website.

[Rex Jones]

Also when the tank top is weirdly shaped to fit.

[The Natural Philosopher]

I fill up with diesel at various different places, but have found one that has three thing

- its reasonably cheap and on my route

- the filling speed doesn't cause the pump to flick off every tow seconds

- the performance is perfectly fine. I have up to half a seconds hesitation anyway as the twin turbos spin up, not to mention the auto box shifting down...