240 General: New (to me) 1980 Volvo 244

[john.wigley]

Originally Posted by Laird Scooby

Playing "Devils Advocate" John, your figures are still wrong! Usually the speedos in our beasts read anything up to 10% fast and so do the odometers so the chances are in real terms, whatever you averaged in your 244 was really 21-23mpg.

Quite possibly, 'L.S.'. But, being relative, my figures will still stand direct comparison with Alan's and those of similar cars, unless, of course, they are using absolute figures based on scientifically calibrated speedometers. Even then, there would presumably still be some small discrepancy based upon tyre wear?

After that tongue-in-cheek pedantry, fuel economy is still really only a guide as to what the engine is doing at any given time. I always think it's more about the consistency with a datum point, rather than specific instances of extreme (good or bad) economy.

There I do agree with you. Variation against a known average can also warn of an impending problem and the need for investigation. I once detected an incorrectly fitted fuel filter on my 944 that way. When I was doing regular commutes of up to 200 MPD, I could even detect 'seasonal' variations in the car's consumption when driven under otherwise near identical conditions.

The "fascination with instantaneous consumption" came from the fact the XJ40 (which both Alan and i have owned) had a trip computer as standard which not only showed fuel economy but distance (two separate trip meters built in if memory serves), speed, fuel used, range and so on - can't remember all the functions but there were quite a few.
Being a near-2T car with a 226bhp 3.6L engine (or 240bhp 4.0L engine depending on age), it could achieve some seriously scary instantaneous figures!
Almost any car will get down to single figures under acceleration, particularly when cold. It's simply the fact that we don't normally see this and therefore aren't aware that it isn't more widely discussed.

I agree that this is not normally a talking point for the reasons that you state, but - I repeat - what is the point? It's essentially academic; lets say that my car does 8 MPG under acceleration while yours does 10. Unless one of us is driving predominantly in a city and the other mainly on free-flowing roads, it will make very little overall difference over an extended period. As I said in my earlier post, there are so many variables that affect specific fuel consumption that, at best, it can only be a guide as to what others with similar cars might expect. Even the manufacturers wrap their official fuel consumption figures in caveats, and they are produced under laboratory conditions.

Regards, John.

[Stephen Edwin]

And re fuel consumption, taking as given that top up to top up is still not an absolute way of measuring

.... there is then that when some people report their car's consumption it sounds a bit like I popped down the road and up to see aunt Ada and chucked in a few squirts of gas so the mpg is increased to X mpg and therefore the job I have just done has achieved an improvement. Yes that is a, small, exaggeration of some posts.

I guess a fair few members keep a notebook and average out over time and miles. For the same purpose. I find useful an app. MPG Calculator. (The results are worrying me. I am working on it, slowly.)

Comrade Stephen Edwin



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[Othen]

Originally Posted by john.wigley

Gentlemen, why the fascination with instantaneous fuel consumption? It only tells you what the car is achieving at that precise point in time, often, as in 'L.S.'s example, when it is working hard under less than optimum conditions.

Of far more interest, I feel, is a car's average consumption. The fact that Alan's Royal Barge is achieving 25MPG is to both his and the car's credit. Alan's, because he is obviously driving it sympathetically, and the car's (which is also increasingly down to Alan's custodianship) because it is maintained to optimum efficiency. I, and I suspect most 240 owners, would have in period considered 25 more than reasonable, especially with a non-O/D auto car. Does it matter that it was only doing 8 immediately after starting from cold on full choke?

In period, without OBC, we weren't aware of instantaneous consumption so didn't worry about it - I sometimes think that it is possible to have too much information! For instance, I know that my present V70 has returned 29.1745 MPG over 12342 miles (the OBC says 29.7). I also know from a simple spreadsheet, latterly without the benefit even of a working fuel gauge, that my previous 745 did 27.3148 over 62746 miles. Those figures tell me that the cars were in a reasonable state of tune with no untoward problems (slightly binding brake, for example).

Having said all of that, it is still possible to be surprised. Our '81 244 averaged a consistent 23 - 25 MPG under normal operating conditions at home. The first time that we took it to Sweden, when we drove across the country (500KM) at an almost constant 90K/h, it exceeded 30 by some margin!!

There are so many variables associated with fuel consumption that I feel that an average figure, measured over as long a distance as possible, is the only reliable guide to a car's performance. Even then, another driver may achieve as much as +/- 10% variation in the same car driven under similar conditions, simply due to differences in driving style.

Stop fretting over the R.B.'s thirst, Alan - it really is quite a moderate drinker! We have been spoiled by the high fuel efficiency (not without cost) of modern engines and instantly available read-outs. As you recognise, it is a product from an earlier, much simpler age. Enjoy it in that spirit; the odd MPG either way is not going to make much difference in an annual mileage of a few thousand miles!

Regards, John.

Hi John,

You are right: the instantaneous fuel consumption is pretty irrelevant, and that is more or less where all this came from. The XJ40 4.0l I had about 25 years ago was the first car I'd owned with an onboard computer, one of its functions was instantaneous consumption, which I recalled could be a bit scary. Coincidentally Dave and I had both owned XJ40s in the past, and shared similar recollections of the onboard computer (which was still novel at the time).

I can't remember the exact figure, but the average consumption wasn't too bad for such a big and comfortable car. I sometimes used it to commute from Newbury to Feltham (so 90% motorways and dual carriageways) and I'm pretty sure it did well over 20MPG - probably 25MPG. It was supremely comfortable with a cabin like an Edwardian mans' club.

We have discussed the RB's thirst previously - I'm pretty happy with 25MPG, particularly as I use it exclusively for shorter journeys. I don't measure it accurately: I just reset the odometer whenever I fill up and divide the mileage by the fuel bill after converting litres to gallons in my head. Now the RB is largely sorted out it has settled on 25MPG.

Best wishes,
Alan

[Laird Scooby]

Originally Posted by Othen

Hi John,

You are right: the instantaneous fuel consumption is pretty irrelevant, and that is more or less where all this came from. The XJ40 4.0l I had about 25 years ago was the first car I'd owned with an onboard computer, one of its functions was instantaneous consumption, which I recalled could be a bit scary. Coincidentally Dave and I had both owned XJ40s in the past, and shared similar recollections of the onboard computer (which was still novel at the time).

I can't remember the exact figure, but the average consumption wasn't too bad for such a big and comfortable car. I sometimes used it to commute from Newbury to Feltham (so 90% motorways and dual carriageways) and I'm pretty sure it did well over 20MPG - probably 25MPG. It was supremely comfortable with a cabin like an Edwardian mans' club.

We have discussed the RB's thirst previously - I'm pretty happy with 25MPG, particularly as I use it exclusively for shorter journeys. I don't measure it accurately: I just reset the odometer whenever I fill up and divide the mileage by the fuel bill after converting litres to gallons in my head. Now the RB is largely sorted out it has settled on 25MPG.

Best wishes,
Alan

Errr........ yeah................ what Alan said! ^^^^^

Purely as a point of interest or a side point, depending on level of interest, mine was a 3.6 Jag Sovereign Alan, on an F/1989 registration. One of the last 3.6s to come off the line i believe before they stretched it to the 4.0L version - both engines examples of the better straight 6 Jaguar fitted to the XJ40 and XJS (there was never an XK straight 6 in the XJS) but the/your bottom line is the RB is largely sorted and returning a consistent 25mpg - that's your known datum so anything consistently higher is a bonus (and cause to question your arithmetic maybe) and anything significantly lower, especially if it's worsening or remains low over a prolonged period is cause to investigate things.

I've just filled my beast up, taking into account a near-end of period top-up and the fact it was idling for ~1hr during the MoT test yesterday and overall, it averaged a smidge under 24mpg.
Knowing the previous tank averaged 20mpg on similar running except for a 130 mile round trip, i took the 130 off the miles i'd done, divided by 20 to get fuel used over the rest of the tankful and worked out during the 130 mile trip that i averaged a whisker under 29mpg at a cruise-controlled (indicated) 77mph and a GPS 70mph on what was mainly a dual carriageway trip.

The MoT did reveal something that points to the higher than average consumption, the CO was reading 1.88% so a bit on the high side.
After the test i got the tester to put the machine on manual and tweaked it down to 1.17% so that should help matters!

[Stephen Edwin]

Originally Posted by Laird Scooby

I've just filled my beast up, taking into account a near-end of period top-up and the fact it was idling for ~1hr during the MoT test yesterday and overall, it averaged a smidge under 24mpg.
Knowing the previous tank averaged 20mpg on similar running except for a 130 mile round trip, i took the 130 off the miles i'd done, divided by 20 to get fuel used over the rest of the tankful and worked out during the 130 mile trip that i averaged a whisker under 29mpg......

Thank you David for that useful post.

Er. Did you forget to mention your visit to Aunt Ada?

Comrade Stephen Edwin



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[Stephen Edwin]

Originally Posted by Othen

..... I don't measure it accurately: I just reset the odometer whenever I fill up and divide the mileage by the fuel bill after converting litres to gallons in my head.

Thank you for that useful post.

What conversion factor do you, usually, use in your head? Anyway as you are an Apple or i phone user. Go get the app. It does all the calculations and will give a result in mpg.

Comrade Stephen Edwin



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[Othen]

Originally Posted by Laird Scooby

Errr........ yeah................ what Alan said! ^^^^^

Purely as a point of interest or a side point, depending on level of interest, mine was a 3.6 Jag Sovereign Alan, on an F/1989 registration. One of the last 3.6s to come off the line i believe before they stretched it to the 4.0L version - both engines examples of the better straight 6 Jaguar fitted to the XJ40 and XJS (there was never an XK straight 6 in the XJS) but the/your bottom line is the RB is largely sorted and returning a consistent 25mpg - that's your known datum so anything consistently higher is a bonus (and cause to question your arithmetic maybe) and anything significantly lower, especially if it's worsening or remains low over a prolonged period is cause to investigate things.

I've just filled my beast up, taking into account a near-end of period top-up and the fact it was idling for ~1hr during the MoT test yesterday and overall, it averaged a smidge under 24mpg.
Knowing the previous tank averaged 20mpg on similar running except for a 130 mile round trip, i took the 130 off the miles i'd done, divided by 20 to get fuel used over the rest of the tankful and worked out during the 130 mile trip that i averaged a whisker under 29mpg at a cruise-controlled (indicated) 77mph and a GPS 70mph on what was mainly a dual carriageway trip.

The MoT did reveal something that points to the higher than average consumption, the CO was reading 1.88% so a bit on the high side.
After the test i got the tester to put the machine on manual and tweaked it down to 1.17% so that should help matters!

The Jag straight 6 was a beautiful thing for an engine Dave :-)

29MPG is excellent for a large car - you must have it just about sorted now.

I'll have to think of some reason to take the RB on a longer journey to see what it is like on a run. Bob and I are planning to visit some friends (including his best friend Bella) at Pentney (near King's Lynn) some time in October, that would be about a 130 mile round trip - mostly on the A47. Normally we would use the Skoda estate for that trip, but we might just use the RB this time just to try it out. It might be interesting to see what average consumption we get on a longer run - watch this space.

Alan

[Dippydog]

The XJ I had was the straight six 3.2 AJ 16 engine-rather than the earlier AJ 6 as fitted to XJ40s.I used to average 27mpg with it. Average fuel consumption doesn't bother me per se[otherwise I wouldn't run the cars I do]but as others have said it can be a useful indicator of problems if it begins to vary fom the norm.Much like when I buy a new[to me] car I drive it about for a week without the radio on listening for the noises it makes,then I can detect even with the radio on if it starts making different noies which might warrant investigation.

[Othen]

Originally Posted by Dippydog

The XJ I had was the straight six 3.2 AJ 16 engine-rather than the earlier AJ 6 as fitted to XJ40s.I used to average 27mpg with it. Average fuel consumption doesn't bother me per se[otherwise I wouldn't run the cars I do]but as others have said it can be a useful indicator of problems if it begins to vary fom the norm.Much like when I buy a new[to me] car I drive it about for a week without the radio on listening for the noises it makes,then I can detect even with the radio on if it starts making different noies which might warrant investigation.

I think the X300 was a bit lighter than the XJ40 due to the largely aluminium chassis DD, which probably accounts for the better fuel consumption. I always liked the look of the X300 but have not owned one.

With the RB (40 years old) I do the opposite and turn the radio up a bit so I can't hear the noise!

Alan

PS. I'm joking about the last bit :-)

PPS. I misremembered the bit about the aluminium chassis, that was the later X350, not the X300. It must be the dementia setting in :-)

[Dippydog]

Turning the radio up certainly "cures" a lot of problems! Can't recall what the X300 weighed I know my Omega[in Elite trim so heaviest of the range] tops a ton and threequarters but will return mid 30s on a gentle[60-70mph]long run and low 20s round town.