Does anybody else’s diesel fuel economy drop off in winter?

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Does anybody else’s diesel fuel economy drop off in winter?

49 posts & 38 voices | Started 2 years ago by Harry_the_Spider | Latest reply from Smee

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5lab - Member

glenh - Member

sharkbait - Member

Surely the alternator is always producing power? It doesn't disconnect from the engine when it's not required (almost never) so it would make very little, if any, difference to the draw on the engine.
I could be wrong though.

It does disconnect on some cars (such as newer bmws) and just connects under braking.

in fact, the volvo 480 (1989 onwards) used to disconnect the rear heated screen when you floored the throttle so as to cut loads on the engine and move you faster. Great idea imo

Posted 2 years ago #
Flash - Member

I think you'll find air density is the issue. As it gets colder the air density increases, this means your car has got to push harder to get through it.

I'm surprised at some of the answers on here, have none of you heard of Occam's Razor?

Posted 2 years ago #
djglover - Member

Is that like Shatner's Bassoon

Posted 2 years ago #
5lab - Member

Flash - Member
I think you'll find air density is the issue. As it gets colder the air density increases, this means your car has got to push harder to get through it.

not so sure it'd make much of a difference. According to here

http://www.engineeringtoolbox.com/air-temperature-pressure-density-d_771.html

at 0C (30F) the density is 0.081 lb/ft^3

at 20C (70F) the density is 0.075 lb/ft^3

or 8% more from mid-summer to depths of winter

Posted 2 years ago #
TroutWrestler - Member

The damp carpet could be a leaky heater matrix. Keep an eye on your coolant level.

Posted 2 years ago #
DrP - Member

I'd say it was all about air density.
Colder air is MORE dense.
In order to maintain a similar air-fuel ratio, the denser air requires more fuel.
This is what the 'air density' sensor on the carb measures.

Denser air = more fuel.

On a similar but different note, the 'leaner' a fuel mixture (to a point), the better the burn therefore the more power can be had with better fuel economy, hence mhy ECU tuning is important. The 'stock' tune is often richer than a tune that will deliver max power, in order to allow for variation and to prolong engine parts.

DrP

Posted 2 years ago #
spooky_b329 - Member

If the air entering the engine is denser, won't to ECU being fuelling slightly higher to match it? If true, you've gained a smidgen of power/performance, at the expense of economy.

Edit: Beaten to it by DrP...should check for a 2nd page before posting

While we're on the winter driving thing, how many people still leave their car ticking over in the morning for it to warm up before driving? You're knackering your engine as it takes ages to warm up at idle, get in and drive gently and it'll be well on its way to normal temp within 5 minutes

Posted 2 years ago #
bigbloke - Member

For the record fuel is denser when its cold.

Posted 2 years ago #
footflaps - Member

As modern cards are all closed loop feedback systems, denser air / fuel will just mean less volume of fuel is used ie the injectors inject less to get the same power.

Posted 2 years ago #
bikewhisperer - Member

An old mate of mine with a diesel landrover used to cover half the radiator grill with tape in the winter to speed up the warm up. Prob no risk of overheating so makes a lot of sense. In theory a hotter engine will be more thermally efficient anyway.
On a side note, has anyone else used that B30 biodiesel from morrisons? Boy does that stuff suck in the cold!

Posted 2 years ago #
deus - Member

it's got to be the density, imagine driving around at -190°C, ther air will mostly be liquid, that drag would be ridiculous!

do they still put benzene in diesel in the winter to stop it waxing?

Posted 2 years ago #
Flaperon - Member

Dunno, but my average has gone from 52 to 39 after refuelling last week. Not impressed, though inclined at the moment to blame Esso instead of the cold weather.

Posted 2 years ago #
esselgruntfuttock - Member

Mine does, but I put it down to the simple fact that as I'm only travelling 15 miles to work each way, the engine doesn't get to it's most efficient working temp as quick as in summer. As well as what Doctor P said.

Posted 2 years ago #
metalheart - Member

Diesel Golf here.

Dropped about 10% (and it was serviced in November).

Running the heater and fan on and up higher and longer as misting up and to defrost the windshield. More use of wipers to clear windscreen just to see. Electric on the rear windscreen (and mirrors) plus engine running while scrapping off the ice must contribute...

Posted 2 years ago #
Smee - Blocked

There is some amount of pish talked on here.

Posted 2 years ago #

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