Unxeplained increase in MPG

[jones325i]

My dad's 2002 E46 330d Auto that he's had from new has suddenly improved in fuel economy. It's showing 40mpg on the computer, and previous best over the last several years was 36. He's worked it out for himself recording the fuel needed to fill up after a known distance of about 400 miles and it really is achieving this figure (he's only ever gone by the OBC figure previously).

He says his driving style hasn't changed and that he noticed the change on the OBC figure during the course of one journey, whereas it never normally changes by more than a few tenths.

My feeling is there's something wrong with the car (maybe boost is down?) but he hasn't noticed anything different yet and says it still 'goes well'. He drives quite briskly but probably doesn't use full power very much. They live quite far from me so I haven't had a go in it recently.

Any ideas as to what could be causing this?

[pilchardthecat]

Could be anything, my e46 330d was the least reliable car in the universe! Could be clogged injectors/under fueling.

Does it emit a caustic stench from the exhaust? may or may not have white smoke

[Ash From Flux]

The first, "Getting too many MPG" thread?

In all seriousness though, don't question it. I wouldn't rule out witch-craft but on the off chance, I guess a service would relieve worry ;-)

[jones325i]

pilchardthecat said:

Could be anything, my e46 330d was the least reliable car in the universe! Could be clogged injectors/under fueling.

Does it emit a caustic stench from the exhaust? may or may not have white smoke

Not that he's noticed but I will ask. Cheers.

Ash From Flux said:

The first, "Getting too many MPG" thread?

In all seriousness though, don't question it. I wouldn't rule out witch-craft but on the off chance, I guess a service would relieve worry ;-)

Ha

I'm afraid I have to question it. Nothing comes for free!

[rj1986]

Maybe those fancy, new, more efficient fuels are working?

[MacW]

Same thing happened to my 350Z a few months ago.

My phone had just had a software update so I put it down to that

[barker22]

He hasn't just turned 60 has he?

[Crusoe]

Fuel stations have probably switched to winter diesel now in the uk, first frosts and snow up here (north east Scotland) recently. That and the lower air temperature with higher moisture is probably giving more power to the engine and making him lift off a bit more on the throttle.

Edited by Crusoe on Thursday 10th October 17:12

[gubbabump]

same thing for me a few months ago, was averaging 23.9 - came back off holiday, have averaged 26.4 ever since, drive same route, same fuel, no explanation why.

[MC Bodge]

Somebody borrowing the car and giving it an Italian tune-up?

[fjord]

My E46 320d was running at 30mpg last winter.

When summer diesel and warm weather came, i jumped it up to 42mpg. Not long now before cold diesel comes back in and my mpg plummets

[JimmyTheHand]

someone I worked with had the air-con fail which increased his MPG, there were a couple of other things that died as well and seemed to increase performance - but that was a large Saab from approx 1990 IIRC

[delmatt]

Has he changed the make of diesel he uses? I drive a Volvo S80 d5 and recently a friend of mine told me I should try Esso diesel as it was more economical than other makes.....I thought he was talking stupid but decided to give it a try even though my nearest Esso is pennies a litre more than the supermarket and I don't get Nectar points. I now get between 45 and 60 more miles per tank full every time I fill up. Is this the answer maybe?

BTW I fill up at least two or three times a week so the change is well worth while even though it costs more per litre overall I am better off.

[JM]

Crusoe said:

Fuel stations have probably switched to winter diesel now in the uk,

fjord said:

Not long now before cold diesel comes back in and my mpg plummets

Can't both be right, can you?


And do UK stations really use a different diesel in winter?

[fjord]

JM said:

And do UK stations really use a different diesel in winter?

http://en.wikipedia.org/wiki/Winter_diesel_fuel#United_Kingdom

[JM]

fjord said:

http://en.wikipedia.org/wiki/Winter_diesel_fuel#Un...

Not sure how much to trust that article, as the BS number for diesel is wrong.....

[Crafty_]

Get an emissions test done, check its not lean (dodgy MAF, lambda sensor etc..)

[trackerjack]

barker22 said:

He hasn't just turned 60 has he?

Hey you I am 62 and no sign of growing up or slowing down yet and I get my zimmer up on two legs when cornering!


I reckon his MPG has improved because he has got rid of the body he had in the boot.

[anonymous-user]

Is there a small melon trapped under the accelerator?

[james280779]

weather has dropped in temperature so it will be a combo of two things. car probably has auto climate control? Everyone knows Aircon uses more fuel. now it working less and therefore using less fuel as the aircon is not on.
Also lower temperature increase engine performance. The cooler air increases bhp and improves mileage. This is why so many people put on aftermarket air filters and reposition them at the front of the car to get the cooler air. Intercoolers work the same way providing cooler air to the turbo.

I noticed a massive drop in performance in my Lotus Esprit Turbo when I moved to the tropics, local expert said its just the way it is because of the higher air temp.