Car MPG

Orion21

Orion21

Orion21

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20 Feb 2006
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343
I have a Vauxhall Astra 1.6 Club (August 2005 first reg). Recently I decided to try and approximate my mpg after filling up with petrol. I got roughly by my calculations 34-35mpg from the full tank of petrol to near empty.

Does that seem low for the car, I had expected it to be nearer the 40mpg mark?

If it is low is it likely to be caused by car age / compenents wearing out and the car generally becoming less efficient?

Or by the use of the 'climate control' in the car (CD / Radio is also on most of the time when in car)? I didn't think these would make a significant effect on the car mpg though and might be powered via the battery anyway?

I'm not sure if the 'climate control' can be turned off, I assume putting it in the 'neutral' position of the knob would do that but I think mine must not be working properly as it still gives out hot air when in this position so I normally have it halfway or full turned to the cool side. Not sure if this could be affecting mpg?

Wondering if I either need to look into getting something fixed in the car or possible changing car (as I am thinking of doing this anyway but may do so sooner to avoid bills and get better economy or a better car and same economy).
 
I am not sure if an alternator experiences a heavier load due to more amps being required by the electrics (e.g. stereo) but if I had to guess I would say it would. The alternator is a parasitic loss (steals power) on the engine.
An aircon compressor also runs off a belt on the engine, but only it engages onto the pulley when the A/C is activated. When it is off the A/C takes no power from the engine other than a simple bearing that the pulley runs on.

I would say that a regular stereo will make little to no difference on mpg, provided you haven't got it loaded with rude boi stereo equipment. The A/C will certainly lower your mpg as the energy required will have quite an effect on a smaller engine.

The things that affect mpg the most are how heavy your foot is and lots of short trips.
 
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That seems about right for mixed driving...

In reality tests most cars don't get there claimed figures...

Mine says it's was getting upto 37mlg on the motorway today's, realistically ill be lucky to have seen 27 all in..
 
PMKeates said:
How did you calculate the MPG?
Click to expand...

Litres of fuel used (estimated from buying a full tank of petrol and using to near empty), converted this to gallons. Also had mileage from resetting the trip computer when I had filled up and divided the gallons into this.

That said I do mainly use my car for commutes so I can be in traffic, even on the motorway / dual carriageway, tends not to be so bad on home journies though as I tend to leave at 6pm or later if I have go to a club / class that day before going home. So return journey is normally a more constant speed, although still has city driving to get onto the dual carriageway / motorway.

I'd say about 2/3rds my journey is motorway / dual carriageway in terms of miles driven.
 
why did you think you would get 40?

That seams about right tbh. I had a 1.8 astra mk4 and is was pretty poor on fuel, allways below 30. the 2.2 was about as economical and had the extra poke.
 
Orion21 said:
Litres of fuel used (estimated from buying a full tank of petrol and using to near empty)
Click to expand...
That will have an effect - you probably didn't get anywhere near empty. Easiest way to be sure is to fill the tank and reset the trip, drive around a normal daily/weekly route, then refill again and record the litres that went in and the mileage.
 
There's an app for android called fuel log & I guess similar for other phones.
I do short journeys around town & get 27mpg from a celica 1.8 & previously got 23mpg from a mondeo 1.8.
I usually leave the climate control on cold/no external circulation until the engine has warmed up so that it warms up as fast as possible & delivers the best mpg.
 
p1RATE said:
why did you think you would get 40?

That seams about right tbh. I had a 1.8 astra mk4 and is was pretty poor on fuel, allways below 30. the 2.2 was about as economical and had the extra poke.
Click to expand...

Parkers had a figure of about 43mpg which I assume is the combined figure, I just expected it to be nearer to that.
 
Log it over 4 or 5 fills.

Next time you get petrol, brim it and zero the counter.

Now on the next refill, keep your fuel receipt (you may have to ask for a vat receipt at some places to get the figures printed on it) and note how many miles you've done. zero the counter.


Repeat the refill and logging until you have about 4 or 5 near empty to full readings. Then calculate on the total figures.

Check your tyre pressures are as they should be, low pressure in the tyres will make you use more fuel.


Is the car due a service? Replacing the following will give you optimum fuel economy and keep the car in good order : oil + oil filter, air filter, spark plugs, fuel filter.
 
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