Fuel consumption?

[martinminor89]

Hello all!.

I've got a 70" Minor, and I've got a question that I'd like to basically have solved before Tuesday (MOT Day).

I topped up the minor on 16th June with £15 of unleaded at Morrison's. Today, I filled it up again, same place, same amount. After working out my mileage since the 16th, I'm coming up with the total of 52.1 miles that the car has driven since I last topped it up. Now, here's the thing, I traveled to Wales from Wigan last month, which was 127 miles away, and ran it on £15 of petrol, this time however, I'm doing less than half that on the same amount of petrol.

I believe my mile counter to be a little buggered, as occasionally I have to tap it for it to show the correct speed I'm doing, could it also be that mile reader needs the same treatment to get it to register?.

I do mostly city driving, and use the correct gears, not too much gas either. I know minor's wouldn't have the fuel economy of today's cars, but surely it's got to be better than what I'm getting at the moment. Does anyone have any tips to improve it, or rather what could be the reason to why the fuel economy has suddenly dropped. I'm not well up on cars as this is my first actual car for myself, so excuse me if I don't exactly get what you're saying at first.

Hope someone can help!.

[beero]

£15 is about 3 gallons, so 127 miles is about right, but 52 is not. First check tyre pressures and make sure your brakes are not binding. Take it for a run for 2-3 miles and see if the brakes feel hot when you touch the wheels.

[liammonty]

Firstly, you can't work anything out accurately without filling the tank, and then filling it again (to the brim) so it's not worth trying to work it out unless that's what you're doing. Secondly, the figures that you've quoted don't actually sound disastrous if you're doing short journeys. Finally, fuel consumption and emissions have no bearing on an MoT for a Minor, so I wouldn't worry about it unless you have visible smoke from the exhaust.

Bear in mind that town driving uses far more petrol than a long out of town journey, so to be honest, the sort of figures you're quoting aren't any great surprise.

[Big Jim]

If you are doing a long run , you could use your satnav to give you a good idea how wrong your speedo/milometer is .

[TvdWerf]

Do not forget the car position.
I have one station to fill my Prius, when I fill him going home, I can put maximal 54 Litre in the car, but when I go to the other direction, it is maximum 45 Litre ;)
Just because the street is not flat.

[simmitc]

I've got a 70" Minor

Has it been shortened? My references give the length as 149.5 inches

a 948 cc car in good condition should return an average of around 43 mpg whilst the 1098 cc vehicles should return about 35 mpg. Both fingers can be considerably improved by slow careful driving and worsened by harsh fast driving.

As above, use a satnav or known measured distance to check you odometer. To check the consumption, fill the tanl, drive a known distance and then refill the tank. Divide the litres purchased by 4.54 to give gallons and then the distance by the gallons. Thus 125 miles on 3.5 gallons would be 35.7 mpg.

If your consumption has worsened suddenly then look for a leak - that could be anywhere, but either the tank or the flexible hose from the pump to the carb are strong contenders. If the brakes are binding then that could do it, but you would probably notice a distinct lack of performance and smell the shoes/drums as they got hot.

Has the car been converted to disc brakes? If yes, then was the master cylinder modified correctly? Failure to carry out the modification can lead to the discs binding to the point that the wheels lock!

[martinminor89]

That's a lot of helpful information to be honest. I'm actually glad I posted here, thank you to everyone for your responses. The brakes have been upgraded, You have to go a little heavy on them to get it to stop, but even in wet weather I haven''t noticed any wheel locking.

The tyre pressure is something that sprang to mind, I'll have to get on to that anyway as I haven't done it in the 2 months I've had the car. As for the fuel tank leaking, sadly I don't think there's enough time to fix that now before Tuesday, so at least if that's what's wrong, the MOT should pick that up easily.

[bmcecosse]

Obviously your odometer is sticking - either fix it or swap the speedo. You can only hope for about 30/35 mpg overall running. There are some heroes on here who claim to get 40+ - they must be the ones I see trundling along holding up the traffic at 30 MPH... or they have the wrong tpm speedo fitted. Why does this have anything to do with the MOT ?

[martinminor89]

Obviously your odometer is sticking - either fix it or swap the speedo. You can only hope for about 30/35 mpg overall running. There are some heroes on here who claim to get 40+ - they must be the ones I see trundling along holding up the traffic at 30 MPH... or they have the wrong tpm speedo fitted. Why does this have anything to do with the MOT ?

Because I'd like tips to see if there was anything I could do before it incase it was the fuel tank or such

[amgrave]

If it was a leak that might fail an MOT I would have thought you could smell it, or is that the case and you have not said.

[martinminor89]

If it was a leak that might fail an MOT I would have thought you could smell it, or is that the case and you have not said.

I haven't said amgrave, as I also don't think it is due to, as you say, I'd be able to smell it. There's no smell at all coming from it, not even any funny smells, so I'm not even sure if the brakes would be binding. Thing is, i mentioned the fuel tank anyway due to not having the car long, and not knowing if it actually was that all along

[bmcecosse]

You must have an idea how far you have travelled - even if the odometer is faulty. What final drive is fitted to the car - and what tpm speedo?

[martinminor89]

I have a fair idea, and I wouldn't say it's 50 miles, I'd say more. And could you explain the last bit of your question BMC as I'm unsure what you mean

[simmitc]

He's referring to tpm = turns per mile. Speedos are calibrated differently depending on axle ratios and tyre size and profile etc. The cable may complete 980 turns for every mile covered or 1053 turns for every mile (example figures, not actual MM values)
. The calibrated value should be printed on the speedo dial in very small digits - but sometimes speedos have been recalibrated for different jobs! The other question refers to the final drive ratio fitted to the axle - there can be different ratio differentials. However, theses would not change suddenly, you would know if you had fitted a replacement axle!

[liammonty]

I doubt it's the odometer that's out due to TPM or whatever (incidentally, the odometer will likely read OK even if the speedo itself sticks) as the 127 miles travelled on £15 of fuel gives over 40 mpg (based on an assumption of £1.10 / litre). It sounds as though this is just a case of short journeys really hammering the fuel economy (which is what it does, unfortunately). Try to minimise use of the choke where possible - you didn't accidentally leave it out did you?!

Regarding the more recent post, a lack of 3rd gear isn't going to help the economy, although like poor fuel economy, it won't affect the MoT

[Chipper]

Firstly, you can't work anything out accurately without filling the tank, and then filling it again (to the brim) so it's not worth trying to work it out unless that's what you're doing.

I hear this quoted often on motoring forums, and find it rather puzzling. I find I can work out quite sensible mpg figures by running the gauge down to the empty/zero mark (which, invariably on most cars means there is still some left in the tank), then filling up with say, 5 litres or a gallon (4.55 litres), then seeing how many miles I can go before the gauge returns to around the empty mark.

Say you put in 5 litres of fuel, that equates to 5/4.55 = 1.098 gallons. Say you then achieve 40 miles out of that 5 litres, you simply divide 40/1.098 to get the mpg figure. If you do this often enough, you can get a good idea of what the average fuel consumption of the vehicle is.

I know that some folk say it's risky to run the tank so low in case it sucks up sediment, etc., well that may be true if it's a car that has been sat around for yonks with stale fuel in it, but on regularly used vehicles it should present no problems, and of course, you can always carry an extra 5 litres of fuel in a jerry can in the boot in case you inadvertently run out of fuel.

Arguably, if you fill the car to the brim, you are having to lug about a lot of extra weight, which may well have a significant impact on the fuel consumption figures you will achieve.

BTW, the best figures I have achieved out of any car I've owned has been with a 1997 Fiat Cinquecento with the venerable 899cc pushrod engine (Fiat's equivalent to the A-series). It regularly achieves 70 mpg! It easily beats a 1973 Fiat 126 with a 594cc air-cooled twin cylinder that I owned years ago. My 1275cc MG Midget engined Traveller generally returns around the 30 mpg mark, though has occasionally achieved 40 mpg on long runs.

[myoldjalopy]

Yes, but it is better to fill up as liamonty says because then you get a more accurate average over a longer period of driving.
I have to say my fuel consumption improved from around 37mpg to around 43mpg after fitting distributer doctor points, filling the tyres to 30psi and driving 'considerately' (and no, that doesn't mean pootling round at 30mph!).
It is a 948cc engine so ties in with what simmitc says.............

[amgrave]

Thank you for that "myoldjallopy". I have a 1963 1098 and did the London to Brighton run last year. Filled up before and filled again when finished and when I checked the consumption I found it worked out 42.2 MPG. I had wondered if I had done it wrong so checked several time again and came up with the same answer. I thought the figure was unbelievable for an old car but you have confirmed it is possible. Only mods are electronic distributor and alternator, with spark plugs set to 34 thou.

[myoldjalopy]

If the 'old car' has an engine in good condition then it should be possible to get close to tests undertaken when the car was introduced. Some research shows that, for Morris Minor saloons:

803cc engine car as tested by 'The Motor' magazine gave 39.3 mpg
948cc engine car as tested by 'The Motor' magazine gave 46.5 mpg
1098cc engine car as tested by 'Cars Illustrated' gave 42.7 mpg

These, I guess would be for steady driving. Of course, if the engine is not in tip top condition and set up correctly don't expect these figures. And as pointed out earlier, lots of short trips and town driving will increase consumption..................

[liammonty]

Firstly, you can't work anything out accurately without filling the tank, and then filling it again (to the brim) so it's not worth trying to work it out unless that's what you're doing.

I hear this quoted often on motoring forums, and find it rather puzzling. I find I can work out quite sensible mpg figures by running the gauge down to the empty/zero mark (which, invariably on most cars means there is still some left in the tank), then filling up with say, 5 litres or a gallon (4.55 litres), then seeing how many miles I can go before the gauge returns to around the empty mark.

Say you put in 5 litres of fuel, that equates to 5/4.55 = 1.098 gallons. Say you then achieve 40 miles out of that 5 litres, you simply divide 40/1.098 to get the mpg figure. If you do this often enough, you can get a good idea of what the average fuel consumption of the vehicle is.

The reason you hear it quite often is because it's the only accurate way to do it. Granted, if you are calculating figures over numerous tanks-full using the method you use, then the error will become less, but the OP is basing his calculations on one or two fill-ups. It seems fairly obvious that adding a just a gallon and then relying on the fuel gauge as a definitive indication of how much fuel you've used is going to introduce a huge margin of error. The fuel gauge isn't exactly an accurate piece of equipment Even doing it that way (i.e. relying on the gauge to indicate when you've nearly reached 'empty' starting with a full tank of fuel would be very inaccurate (although 6.5 times less so than using just the one gallon!).

Please don't think that I'm trying to be funny here, but I just feel that as the OP has posted some odd fuel consumption figures, the best thing to do is to make sure that the best way to actually calculate the MPG is explained - that way, at least he can figure out whether he really has an issue worth worrying about with his car or not!