True MPG?

[crickleymal]

Or did you mean how do you use the fuel warning light to calculate mpg? - the distance covered between the fuel light coming on and the next time the fuel light comes on, divided by the litres added between these occurrences, divided by 0.22 will give a reasonably accurate mpg!

Aha! Now I understand, thanks. How consistent is the warning light? I can see how it would be better than relying on the click off on the pumps though.

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Best ways to get top MPG

Avoid braking as much as possible
Turn off any electrical items not needed (esp rear heated screen+blowers)
Check your manual - most cars return best MPG at 56MPH (not sure why)
A full tank of fuel weighs a similar amount as a passenger so don't keep it full unless you are on a long run
Keep boot as empty as possible
Keep windows shut to reduce drag (if its really hot, the aircon will have less impact on fuel economy on the motorway than having the windows open)
"fuel saving" tyres do work but I wish I knew how!
Good quality oils and proper servicing make a big difference
Magnetic "fuel savers" help a little by aligning fuel molecules (Spitfire planes used it originally)
Higher octane fuels can add to MPG but hard to calculate the extra cost/benefit balance

I agree with most of those but:

the 56mph thing, isn't that just the speed at which the measurements are made (or used to be made) to gauge the "extra urban" mpg of the car.

I'm fairly sure the magnetic fuel molecule aligner thing is snake oil.

[Northman]

most cars return best MPG at 56MPH (not sure why)

Do they?

What Car? did some testing (see here), and doesn't seem to think so:

So is 55mph really the efficient speed that it's often made out to be? In short, no.

Peter de Nayer said: 'The results of our tests disprove the idea that there is an optimum cruising speed - around 55mph - below which fuel consumption increases.'

What the results did show was that, basically, the slower you're going in top gear, the more miles per gallon you're doing. . . .

It's all down to wind resistance - . . . .

[Noel Brig]

Aha! Now I understand, thanks. How consistent is the warning light? I can see how it would be better than relying on the click off on the pumps though.

Much more accurate than I ever imagined it would be - you do need to be careful it didn't come on because you were stopped on a steep hill as it may go back off when on the level - but that aside it is nearly as good as filling to brim full.

Do they?

What Car? did some testing (see here), and doesn't seem to think so:

So is 55mph really the efficient speed that it's often made out to be? In short, no.

Peter de Nayer said: 'The results of our tests disprove the idea that there is an optimum cruising speed - around 55mph - below which fuel consumption increases.'

What the results did show was that, basically, the slower you're going in top gear, the more miles per gallon you're doing. . . .

It's all down to wind resistance - . . . .

I think the 56mph (90kmh) was a Brussels hatched figure thought to be the best compromise between journey times and fuel economy.

I would certainly suspect the most economical speed to drive a berlingo at would, as northman suggests, be as slow as reasonably possible in top gear - probably just under the 40mph mark in a mk2, could be a bit tedious on a long journey!

[Northman]

I would certainly suspect the most economical speed to drive a berlingo . . . could be a bit tedious on a long journey!

Surely no journey in a Berlingo is tedious?

[Big_Jim]

I usually brim the tank approx 50 miles after the warning light comes on. I think its very conservative as I often only get 50 litres into the tank before the pump "clunks". Handbook says its a 60 litre capacity but I once got 60.15! Really must have been on fumes that time.

[CandR]

Good points in this thread. Reminds me next time I'm on the motorway to check my odometer (mileometer? kilometreometer?) against the nice little boards (every 100 metres on Dutch motorways) beside the road. I've got a feeling I might find the car thinks it's done less than it really has!

It would be good to know your findings - very unusual for an odometer to read low, my mk2 is 1.75% over and the mk1 was 4.4% over.

Hi Noel - you are right. Had a chance to do it today. More than 100 kilometres on the same motorway. Zeroed the 'ometer at the '36.0' board, and at '136.0' the dash read 95.9. So indeed the car is doing more than it thinks, by 4.1%. ....edit: eerrm - no. I was right, and mine's different to your experience

[crickleymal]

A bit of a thread swerve here but still sort of related. Do you find your interval to the next service going down faster than the miles add up? Sometimes I find mine has dropped by 100 miles when I've only done 80 (measured by the odometer). Now I know it's related to driving style but I'm quite a sedate driver and rarely exceed the speed limit on the motorway. I do about 70 miles a day on the motorway and about another 10 or 20 in the evenings a couple of nights a week.

[Noel Brig]

Hi Noel - you are right. Had a chance to do it today. More than 100 kilometres on the same motorway. Zeroed the 'ometer at the '36.0' board, and at '136.0' the dash read 95.9. So indeed the car is doing more than it thinks, by 4.1%. ....edit: eerrm - no. I was right, and mine's different to your experience

How strange - I have never come across a vehicle before that understate distances. So basically whatever mpg you think you are getting you are indeed getting 4.3% more. (or indeed km per litre - curious, how do you quote fuel economy?)

I am still a little puzzled by your findings - How accurate are the km boards? - what tyre set up are you using?

[CandR]

How strange - I have never come across a vehicle before that understate distances. So basically whatever mpg you think you are getting you are indeed getting 4.3% more. (or indeed km per litre - curious, how do you quote fuel economy?)

I am still a little puzzled by your findings - How accurate are the km boards? - what tyre set up are you using?

That's interesting, Noel. It seemed right to me, because I heard years ago that car manufacturers put a deliberate error on speedometers, so their customers don't break speed limits unawares, and sue the car company! I'd heard that that error was between 1.5 and 2.0 %. So I thought this was normal if a bit much - but actually I've got it the wrong way round...

If our car thinks she's doing fewer miles, then she thinks....... Ah! I'm not so good with numbers, but I suspect, therefore, that when our lady says she's doing the speed limit, she's actually doing 4.3% more, and I'll get a ticket! Oh, dear :justno:....
So you are right indeed, and I've got it all a*se backwards. (good news for my mpg, however!)
The tyres are Michelin Energy Savers, at the correct pressures. Everything else as far as I know is bog standard (she's 10 years old after all). The Dutch kilometre boards are placed every 100 metres (K 1.1, K 1.2, etc.). I assume they're pretty accurate. I'll have to find another long trip with a good long stint on one motorway!
I've got used to the Dutch expressions for fuel consumption. It's expressed as k's per litre: (I get one-in-14!) or litres per 100 k's.
All the best
Richard.

[ron]

In Germany,it's litres per 100 km.Must be a standard thing over there.