Mpg v mph

[Alan Zoff]

I expect some would prefer the use of metric terms but I still work in miles per gallon.

Coming to the UK from central France at the week-end, my passenger suggested we tested the car's fuel consumption travelling at a more modest speed than usual. It's an 11 year old Mazda Xedos V6 (petrol) which has done nearly 160,000 miles. On previous tests, I have normally achieved around 32mph, travelling at the legal maximum or more.

So this time, after filling the tank to the brim, I set the cruise control to 70 rather than 80 for motorway use and kept to all other speed limits. My passenger noted the regn numbers of any Brits that flew passed us along the route.

We still arrived at Calais with time to spare and found amongst the lanes of ferry customers several of the cars that had overtaken us.

I refilled the tank at Dover. 10.1 gallons - 375 miles. That included getting though Paris, although admittedly the peripherique was pleasingly "fluide". On the other hand, in addition to 2 fairly hefty occupants, the car was fully laden with heavy tools and quite a few bottles....

So just by driving at a slightly more relaxed pace, fuel economy went up from 32mpg to 37mpg, a saving of over 15%. I always knew speed made a difference but was surprised how easy it was to achieve this size saving.

I know several of you will tell me you get 50 or 60mpg from your new turbo-charged diesels but its reliability and my DIY maintenance make the comfortable Mazda a relatively cheap car to own overall - it would certainly take some considerable time to recoup the replacement cost if I were to scrap it and buy a new model. As for environmental damage, I imagine the carbon footprint, etc from producing a new car is not insignificant.

[Chancer]

It would have been even more if you were driving a lesser powered car as your Mazda is effectively cruising at either speed, you did actually reduce your speed by 14.8%.

I have a relatively low powered diesel car (110 cv) whose economy drops off significantly at 80 mph compared to 70 and increases significantly if I drop to 60mph, I have found that when towing heavy loads with a large wind frontage it is less economical than when I have borrowed a friends huge Land Cruiser which on normal urban runs without trailer consumes pretty much twice the fuel that mine does.

Another factor is driving style, some drivers seem to find it impossible to maintain a steady speed without constant throttle adjustments, this can make for a very uncomfortable ride for queazy passengers in a powerful bagnole.

I also find that if you are going for all out fuel economy a good driver will get better economy than cruise control as it will use a wide open throttle if necessary to maintain speed on hills, I have an instant readout of fuel consumption and find it makes a real difference (within reasonable limits) if you allow the hill to pinch a few mph from your cruising speed.

[AnOther]

You mean 110bhp of course not CV !

I agree. Overall in day to day driving my Skoda 1.9tdi does a virtually constant 5.4lt/100km (53mpg) but at a cruise controlled 130kph on the motorway it drops to around 6.7lt/100km (45mpg).

[Dog]

It is worth the effort to save fuel especially with the price escalating at an alarming speed.

Dropping the speed of your car as you show makes little difference in travelling time.

When the trusty Mazda finally takes it's trip to the recycling plant a turbo diesel may be on the cards - on local trips I am currently getting 4.2 litres to a 100K.  A 100k is roughly 62 miles so not doing too badly for a seven seater.

Unless I am cut up I hardly use the brakes so save on pads. I only accelerate slowly and in built up areas only enough to get inertia to roll to the the next lights or junction.

I take it easy up hills on the open road and get overtaken then find the overtaker braking down the hill - this really annoys me wasting a free coasting ride.

Don't forget to pump those tyres up.

When I was young and hard up my friends and I checked out all the local petrol pumps and found some that you could trickle fuel from them without registering a price on the pump. It is still worth a try but takes time and the technology of the pumps is better.

It is  worth buying fuel in the morning when it is colder and more dense.

Slow down - chill out - & save money...

[Chancer]

[quote user="AnOther"]

You mean 110bhp of course not CV !

I agree. Overall in day to day driving my Skoda 1.9tdi does a virtually constant 5.4lt/100km (53mpg) but at a cruise controlled 130kph on the motorway it drops to around 6.7lt/100km (45mpg).

[/quote]

I meant horsepower but used the CV as an abreviation for chevaux which was in my head, despite my best efforts my postings and speech are peppered with French terms.

We have the same car, is yours a LHD or have you found a way to change trhe display to litres and kilometres?

Dog. Your economy figures are impressive for (I assume) a non turbo diesel, if you have a petrol engine then unbelievable, I had a 2 litre petrol Galaxy 7 seater that returned around 25mpg, switching to a 90bhp turbo diesel Alhambra brought it up to 34 mpg although i do drive much slower these days, what 7 seater do you have? - I want one! [:D]

[Alan Zoff]

Just Googled some pages about Cruise Control economy and most seem to suggest that on average fuel economy is improved. That's not to say that an individual can't do better - a skilled driver clearly can - but the CC saves having to monitor the speed all the time. I certainly find it relaxing on an empty motorway to let the technology take over and I am happy if that means I am using less fuel than would the average driver. CC almost useless on most UK crowded roads, though.

And yes, the next car will be something more economical but for the reasons stated I don't think there is sufficient upside just yet.

[Chancer]

Cruise control is as good as a good driver in terms of regulation of speed and far more economical than an on and off the pedal driver but it loses out as soon as significant hills are encountered.

A skilled economy driver will accept some trade off of falling speed for economy when climbing a hill, the cruise control will open the trottle wide if needed to maintain speed. Going down the hill the skiled driver will allow the car to overspeed on a trailing throttle or coast to gain inertia (very important if at the bottom there is another uphill stretch), the cruise contol will use engine braking and some even apply the brakes to regulate the speed.

[AnOther]

It is a left hooker Chancer, ex Belgian.

I have no doubt that I could better the CC on a long run but unfortunately I have a dicky right knee which siezes up painfully if kept in the same position for any appreciable period and the average position when driving is particularly difficult so although it goes against the grain CC is a must.

With the totally different, more reclined and stretched out seating pose of my MG, I have no problem with my knee at all and fitted with properly set up later HIF4 SU's it will do 36mpg on a good motorway run at speeds between 70/80mph [:D]

[RicandJo]

If I do 70mph I get around 9 mpg. I can get it up to 15 by cruising at 55!!

:)

[Polly]

At 60mph on motorways I can easily get 40mpg out of 1960s technology and am hardly any slower than in my modern small car machine ... OK so the ride ain't quite so good and it's noisier but folks smile and the dogs get wind in their ears from OPEN windows! It's also a lot more economical on short winter runs.

Ease off the go pedal, chill out AND save on speeding fines.

Toodle pip!

[Dog]

[quote user="Chancer"][quote user="AnOther"]

You mean 110bhp of course not CV !

I agree. Overall in day to day driving my Skoda 1.9tdi does a virtually constant 5.4lt/100km (53mpg) but at a cruise controlled 130kph on the motorway it drops to around 6.7lt/100km (45mpg).

[/quote]

I meant horsepower but used the CV as an abreviation for chevaux which was in my head, despite my best efforts my postings and speech are peppered with French terms.

We have the same car, is yours a LHD or have you found a way to change trhe display to litres and kilometres?

Dog. Your economy figures are impressive for (I assume) a non turbo diesel, if you have a petrol engine then unbelievable, I had a 2 litre petrol Galaxy 7 seater that returned around 25mpg, switching to a 90bhp turbo diesel Alhambra brought it up to 34 mpg although i do drive much slower these days, what 7 seater do you have? - I want one! [:D]

[/quote]

It's a Toyota nothing stops them!

Turbo-diesel Corolla Verso bought new and now nearly 7 years old. Good old bus.

[Dog]

[quote user="RicandJo"]If I do 70mph I get around 9 mpg. I can get it up to 15 by cruising at 55!! :)[/quote]

 

Do you chuck tenners out of the window as you deplete the worlds energy resources?

I bet you just leave it ticking over all night so it's warm in the morning ready to squander more hydrocarbons...

[RicandJo]

I probably use less of the worlds resources than you.....

[Dog]

[quote user="RicandJo"]I probably use less of the worlds resources than you.....[/quote]

Well if you do over 1200 miles a year in that gas guzzler you ain't got much of a head start!

Do you grow your own veg, heat the house and cook with wood?

A mate of mine was nearly killed in a Jeep when it rolled over.

[RicandJo]

About 400 miles per year I reckon, it's just a toy. It's 31 years old though so I reckon I'm saving the world the energy required to make two whole cars. No in all seriousness no I don't grow my own veg (not all of it anyway) and cooking with wood is for boy scouts and Ray Mears ;)

I do commute to work each week though on a 737. And I recall not so long ago ground running a 146RJ at high power for about 15 minutes to diagnose a defect, I think we burned off a tonne and a half of fuel before we figured out what was wrong ;). So maybe I do use more than you......yes I think so!!

Yeah my cousin was nearly killed when he rolled a Jeep down a hill too. Gotta watch em.

[La Guerriere]

Just getting back to the original point for a moment:

We have a SAAB 95 Estate 2.2TID. It functions pretty well at 70 mph / 40 mpg but push it and the consumption rockets. Back off to 60 mph and we go up to 42-45 mpg, but it's very boring. I spend a lot of time putting the roof rack on and taking it off again (+/- 2 mpg or so), and keeping the aircon off unless really necessary.

[AnOther]

Effect of the aircon on fuel consumption is another debatable point. I find it maked no perceptible difference to my fuel consumption.

Mine is actually climate control but I doubt that makes any real odds.

[Alan Zoff]

Aircon was on for most of journey, too. Suppose I could check it with it turned off - but heck, what's the point of having these extras if you don't use 'em?

[Salty Sam]

[quote user="RicandJo"]....... and cooking with wood is for boy scouts and Ray Mears ;) [/quote]

Ray Mears ???? You mean him that watches what the natives do, then shows the viewers 'how to', but in the process creates massive carbon foot prints in his travels ?

You've got got nothing to worry about with your choice of vehicle [:D].

[Dog]

Air-conditioning is powered by a compressor that takes power to drive it. It can put up fuel consumption by 5 to 10%.  Also anything that's powered in the car by electricity puts up your mpg as electricity doesn't come free. Unless you have one of those newfangled hybrid cars that uses a generator as a brake which makes sense but is expensive.

[Chancer]

[quote user="AnOther"]Effect of the aircon on fuel consumption is another debatable point. I find it maked no perceptible difference to my fuel consumption.

Mine is actually climate control but I doubt that makes any real odds.

[/quote]

I had a Sierra with aircon that used to use significantly more fuel when it was swiched on, it turned out that whilst it was functioned +- OK it needed regassing and once done it cycled in and out whereas before it was pemanantly engaged and the fuel consumption therefter became negligible.

When the aircon/climate control was working on my Skoda before the electro-magnetic clutch let go like you Ernie I never noticed any increase in consumption and as you know with the dashboard display you can see even a 0.1mpg instantaneous change.

[Alan Zoff]

My aircon definitely saps power - you can feel the effect immediately it cuts in, and especially when pulling off. But you pays yer money and takes yer choice. I choose to be comfortable.

[Chancer]

Get it regassed Alan, you will be surprised at the diference that it can make, with my old bagnole apart from the fuel consumed I could actually feel the drop in power, once regassed there was no perceptible power loss or increase in consumption.

Dog is of course correct tht it does indeed take power and hence consume more fuel, as does using one headlights but we dont worry about that, there is nothing for free but an aircon in need of regassing really does sap power and picoler the fuel and I suspect wear out the compressor, all that power loss must be going somewhere, probably creating heat.

[AnOther]

A tip:

If you are going to have an aircon re-gassesd do have it leak tested first. It's easy to do and there is no point in re-gassing if a week later it's all gone again !

[Dog]

[quote user="AnOther"]

A tip:

If you are going to have an aircon re-gassesd do have it leak tested first. It's easy to do and there is no point in re-gassing if a week later it's all gone again !

[/quote]

.. and get it done by a refrigeration man at half the cost.