406oc.co.uk

I was wondering if one of our erudite enthusiasts could cast some light on a conundrum I have been pondering for some time. I have noted with various cars, (petrol & diesel), that mpg is always poorer in cold weather, but I'm at a loss to explain it, (much less influence it).

On big Poxhalls I used to run, (24V Carlton, 3.0 Omega), I consistently got 1 mpg less in winter vs summer. With the 406, it's more like 2.5 - 3 mpg. Initially I put this down to longer warmup / less fuel efficiency, which rings true for the petrols. However, I do 30 miles each way every day so I wouldn't have thought it so significant, particularly with the diesel, since it isn't really much thirstier when cold. Also colder air should be denser, giving more oxygen for the same pumping effort and intercooler should be more effective.

The instantaneous fuel consumption defo seems higher at the same speed / same road / colder day - possibly even worse in rain.

Whadya think, folks?

last year when it was very cold my mpg went up
never got to the bottom of it as i was doing the same journey at the same sort of speeds [duel carrigways/moterways]

Cold-start enrichment programme!

The HDi is hopeless at getting heat into the block (that's why they have an electric heater doo-dad for the cabin).

In winter the engine is being constantly cooled by air passing over the sump etc and coupled with the low intake temps the whole process of reaching full working temps takes longer (and more fuel).

Lorriest's say the best intake temp for diesels is about 15deg C, any less and the flame front is 'quenched' by the incoming air leading to incomplete combustion and the driver stamping on the gas a bit more

Some folks play around with blocking over the intercooler and such to bring the temps up but that's ok until you get into the city.......

I used to lose 3-4 mpg in winter.

Also when it's cold you have more electrical items on, i.e. heater, heated rear screen, heated seats, air-con to demist, etc, etc so this all adds up to an increase in fuel consumption too.

Welly wrote:Some folks play around with blocking over the intercooler and such to bring the temps up but that's ok until you get into the city.......

Interesting - the DW12's got two heat exchangers - conventional intercooler and a water-heated jobbie to increase intake air temp during warm up and FAP regens. It has two vacuum operated throttle valves to direct air through one or t'other.

PP2000 displays intake air temp.

If nothing else, I guess you could rig up manual control of the throttles and see if warmer air helps?

My 1.8 is still running at a touch over 40 mixed as per usual.
It was alittle down last year/start of this as I work nights I have a habit of leaving it running to warm up while I yack to the girls.
Probably be the same this year too with the cold mornings coming in.

Yep, starting to drop here too. Computer gives average on this tank as 49, whereas it has been 52 and more over the summer.

It doesn't take much longer to get up to temp, but of course getting to 90 is harder when its colder.

I also thought that:

• colder air is more dense, and
• the colder air cools the wire in the MAF sensor more (so unless this is compensated for against outside temperature this means that the MAF reports more air being sucked in).

Now, if the MAF has decided that more air is being sucked in, then maybe the ECU decides to shove a bit more fuel in...

...but then the engine would speed up, so you'd ease off...

Hmm, I think that all we can conclude from this is that I'm neither an engineer nor a mechanic

I dont really drive correctly to notice a difference in economy, if i learn to drive economically ill let you know, but i know our tractors use more diesel in the winter. As for petrols they seem to heat up nice and quick the fiat no matter how cold had warm air coming from the vents within a minuite
By the way dogslife was your vauxhall the big lotus carlton one by any chance?

Darker mornings/evenings so the lights are on more, heater going full pelt, wipers, heated rear window going, thicker oil means harder cranking, leaving the engine running while I scrape off the ice and/or so I can touch the steering wheel without needing gloves...

They are so paranoid about emissions controls - so they make it that the car has a longer warm up cycle, to get it up to operating temperatures quicker (therefore being more efficient)...

So, depending on how and where you drive it in the first couple of minutes - this will hit your MPG the hardest. I even think that the autoboxes have different shift patterns when cold from memory!

406executiveHDI wrote:By the way dogslife was your vauxhall the big lotus carlton one by any chance?

I wish! Just a common or garden repmobile, like this:

Vauxhall Carlton GSI 3000 24V

Both this & the Omega had a magical ability to clear the outside lane. White cars aint so bad.

rwb wrote:

I think that about covers it

I only got a spread sheet for my D8

One of the worst things about winter is the coldness of the leather seats, i sat down on them with just a vest the other day it said -3 and it aint nice really to sit on them in the winter you need to be wrapped up like your going to the north pole

I wish! Just a common or garden repmobile, like this:

Vauxhall Carlton GSI 3000 24V

Both this & the Omega had a magical ability to clear the outside lane. White cars aint so bad.

Nothing common about those. I loved them (& still do). Senators were great too.

& white cars are great. Hide most little scratch marks & look great when cleaned. My 325tds used to have the same effect on motorways as Hants Police used to have loads of them.

What other cars have you had Doggy? Our tastes seem to be rather similar!