[Petrochemicals (OP)]

Today the motor is averaging 52mpg, this is city driving, traffic lights, junctions, etc. Only a week ago it was averaging 44mpg for the same type of driving. The numbers are via the cars display?

[Eternal Student]

Hi.

   I don't really know where your figures came from.  My car hasn't improved its fuel economy this week compared to last week.  52 mpg sounds unrealistically high for the average motor car, what country did the figures come from and is it all downhill there?

Best Wishes.

[alancalverd]

Oddly, I concur with PC!

For no reason I can think of, Britain's motorways have suddenly become congestion-free and the cities seem devoid of idiots.

[paul cotter]

That's an interesting observation, Alan. Here in Ireland we have had an alarming increase in road deaths over the last two years. There appears to be no shortage of idiots here, maybe we could export some if you feel your country is running short?!!. Driving on an idiot free road/motorway could be actually enjoyable instead of apoplexy inducing. On the mileage question, the boss' car(Renault clio hybrid) will do ~50 to the gallon - I can testify to this as I have been driving it recently as my 20year old Honda civic has gone to the great service station in the sky. The clutch hydraulics failed and I could not source a replacement master cylinder. Now I will have to choose the least worst of the current range of overly complex motors.

[vhfpmr]

More averaging needed.

I was getting little more than 4% variation if I exclude the one year where my driving was materially different:


Car MPG.png (63.38 kB . 1765x710 - viewed 302 times)

[alancalverd]

Not sure where ES is based, but 50 mpg is a reasonable target for a smallish European car using British gallons of gasoline, equivalent to 37.5 miles per USG.

I use a medium (for Europe) SUV - a Skoda Yeti 2 liter diesel that generally averages 52 mpg between weekly fillups but has crept up to 55 this week, despite thrashing around the M25 (London peripheral route) and in and out of central London. 

[Eternal Student]

Hi.

   I don't really know a lot about cars.

   I have a red one with 7 seats but I don't usually put all the seats down.  So I reckon it has the fuel economy of a 5 seater on average.

    I've also noticed the trip computer displays an economy of 0.1 mpg while I'm waiting at the traffic lights.  The hand-brake is holding, so I reckon that's because the earth is moving through space all the time.

    It runs on tyres.   This car has a diesel injection engine while my old one had a petrol injection engine.  I can use the same tyres, the engine just injects them differently.

Not sure where ES is based

   It's a fairly ordinary house with a B rating for energy efficiency but I can't always park the car close to my house and I don't know what efficiency the other houses offer.

Best Wishes.
(perhaps I should keep my day job and not consider a career as a comedian).

[Petrochemicals (OP)]

Hi.

   I don't really know where your figures came from.  My car hasn't improved its fuel economy this week compared to last week.  52 mpg sounds unrealistically high for the average motor car, what country did the figures come from and is it all downhill there?

Best Wishes.

From the car computer display thing. It is a modern car with the small 1 litre eco turbo boost engine. From the uk, round trips so there is as much up as down, standard city driving. Things i think could factor:

1)humidity
2)oxygen content
3)air temperature
4)road surface temperature
5)fresh air as opposed to used air? As in smog, maybe based on wind?
6) car temperature?

[paul cotter]

The presence of headwinds/tailwinds could produce such a discrepancy in motive efficiency, it's hardly likely that the brake thermal efficiency of the engine could be that erratic. Most of one's fuel goes to counter wind resistance assuming careful driving without redhot discs. Note to ES regarding comedy: I had similar aspirations once as Alan had made reference to my "rampant wit"!

[alancalverd]

My travels are almost always out and back the same day. Whether this is effectively a radial or mostly an arc around the M25, I would be very surprised if, just for one week, the wind changed through exactly 180 degrees every day whilst I was visiting my client's premises for a couple of hours!

[paul cotter]

Cyclonic pattern winds. I know I am "scraping the barrel" to find a cause of the discrepancy, what do you propose?

[Petrochemicals (OP)]

The presence of headwinds/tailwinds could produce such a discrepancy in motive efficiency, it's hardly likely that the brake thermal efficiency of the engine could be that erratic. Most of one's fuel goes to counter wind resistance assuming careful driving without redhot discs. Note to ES regarding comedy: I had similar aspirations once as Alan had made reference to my "rampant wit"!

1)humidity
2)oxygen content
3)air temperature
4)road surface temperature
5)fresh air as opposed to used air? As in smog, maybe based on wind?
6) car temperature?
7)air density/pressure

[paul cotter]

I would only rate 1,3 and 7 as having any significant effect, but way less than a STRONG headwind/tailwind.

[Petrochemicals (OP)]

I would only rate 1,3 and 7 as having any significant effect, but way less than a STRONG headwind/tailwind.

3 and 5 i think will be the same thing too! Catalytic converters run on a fuel rich mix in the engine, so a slight uptick in oxygen persentage may yield results, especially if the fuel air mix is set for a high atmospheric pressure/ low humidity/low temperature senario, that is if these modern cars themselves do not automatically adjust for humidity, temperature and pressure

As alan points out, a round trip is unlikely to yield wind or gradient advantage. Talking of gradients, i have often wondered if someone who lives in london achieves better mileage than someone who lives in sheffield, as the latter is quite hilly, all that braking to keep within the speed limit must add up. Its not all down hill from here though.

[alancalverd]

Problem with London is empty bus lanes and a 20 mph speed limit practically everywhere, so even when the traffic is moving you rarely get out of third gear.

[Petrochemicals (OP)]

Problem with London is empty bus lanes and a 20 mph speed limit practically everywhere, so even when the traffic is moving you rarely get out of third gear.

That is the problem everywhere, exept london has this wonderous thing called the underground, you can quite easily live in london without a car at the same time as removing pollution and doing your bit to lower global warming. If only they had put similar infrastructure into all the other congested cities, Birmingham and Manchester wouldnt have the longest commute times in the uk.  Ah well, I supose it would have cost ?100 billion plus.

[nicephotog]

In the 1980s in the USA car manufacturers started to put computers into cars to collect information on performance.
These first computers were manufacturer specific until the industry made a common specification and added Diagnostic data collection.

The specification is known as OBD "On Board Diagnostics" , the USA spec. and there are others JOBD and EOBD (Japanese , European).

When a fault is sensed the onboard computer stores a special OBD "lookup error code" you can find online.
e.g. P1003
Then it switches on the "check engine" light on the dashboard to alert a driver or mechanic to take a look with the OBD reader tool.

I changed the fuel filter in a Holden Captiva diesel recently, unlike the old days before 2000 , there were electric data and power source leads into the filter housing top and bottom, I had to also change the master cylinder and re bleed the brakes because the other master cylinder sinks the pedal to the floor, it had data connectors onto the master cylinder for the ABS unit.

Anyhow, all vehicles on the road legally must have some form of OBD. You can buy particular OBD readers from good engineering and  industrial tool stores.

You will find the OBD data connection port in your car usually to the wall side of the driver in the bottom of the dashboard or just under it if not covered by a plastic inset plate.

Today the motor is averaging 52mpg, this is city driving, traffic lights, junctions, etc. Only a week ago it was averaging 44mpg for the same type of driving. The numbers are via the cars display?

Diesel (drained water from the fuel filter, service done on time)?

or petrol (unleaded , unleaded premium) ?
Does the engine blow more smoke than before and seem less powerful (spark plugs) , (piston rings over 250,000 km's)?
.
Exhaust gas return valve clean?

Bad hydraulic lifters (tappets worn tips on manually tuned valve system)?

Excess carbon build up "on" cylinder - cylinder head internal, it causes loss of correct fuel ignition "moment".

A rare and vague possibility is a fuel leak. Done Any work on the  fuel lines (non screw in lines use a special plug clipping tool). Start the car on a clean level cement area, take a look under it before you start it front and at the back where the tank is underneath, run it for five minutes idling , give it a few revs for a moment, nothing hard (tap the accelerator a few times just after starting ) . When time is up find if fuel and drips have formed on the ground as a stain under the vehicle.

A less common one is water leaking into the cylinders from a blown head gasket. If you must get this tested (there are off the shelf special test kits) always take the vehicle to a "reputable mechanic" not simply down the road!
When I got the Captiva, the guy told me it only has 177,000 km's on the clock and it was serviced regularly and recently.
When I test drove it the brake pedal sank to the floor a number of times, and the automatic transmission skipped over a gear to the top gear.
When I tried to find the transmission oil level I couldn't get a reading, it took two litres to fill it, the correct quantity is 2.5l , the engine oil was black as night (no service there if it ever was changed). The fuel filter was black as night, a wonder the engine ran with any power! It was a bit more powerful after the fuel filter was changed.
I'm getting it to pink slip test for the rego soon.

[alancalverd]

london has this wonderous thing called the underground

Which would be a Good Thing if the suburban stations had big enough car parks!

[Petrochemicals (OP)]

london has this wonderous thing called the underground

Which would be a Good Thing if the suburban stations had big enough car parks!

The idea of a light railway is there are more stations and you walk to a local station.

[Petrochemicals (OP)]

Diesel (drained water from the fuel filter, service done on time)?

or petrol (unleaded , unleaded premium) ?

It still fluctuates so nothing mechanical. It's petrol, so I have wondered about the quality of fuels, whether light distilates are being boiled off or burned, or simply a different quality of fuel or contamination. I feel it is definatley something to do with the air, the humidity content, smog etc.