Fuel Economy Dropped

SHD1983 · Post by **SHD1983** » Wed Sep 27, 2006 6:37 pm

I've got a 2.0ltr HDI (110) and I had been getting ~650 Miles per tank, but for the last month I've been lucky to get over 600 and I've been doing quite a bit of Motorway mileage!

Any ideas why the drop? There's been no drop in power and it's not smoking!

Post by **Welly** » Thu Sep 28, 2006 9:08 am

SHD1983 wrote:I've got a 2.0ltr HDI (110) and I had been getting ~650 Miles per tank, but for the last month I've been lucky to get over 600 and I've been doing quite a bit of Motorway mileage!

Any ideas why the drop? There's been no drop in power and it's not smoking!

*Puts hand up first*

It is fairly simple, you see when you start off in the morning recently the ambient temperature has been as low as 12 deg C, this in turn makes the car run on 'choke' if you like for longer than it would in the summer months when it is warmer.

I have the same issue (as do many other Diesel owners like Golf TDi's).

In the Winter I get 33.6 MPG (purely door to door)

In the Summer I get 37.7 MPG (purely door to door)

So, if I put in £60.00 (14 gallons) I could see a difference of 14 x 4.1 (MPG difference) = 57 miles less on a tank full.

Your getting about 46 MPG in the summer and dropping to 42 MPG in colder weather, about right really.

Thanks,

Welton
Head of Maths 1999 - 2001

I thank yaw.......

miniman · Post by **miniman** » Thu Sep 28, 2006 10:07 am

Who's a clever boy then??

Is that why im only getting 30mpg in mine. Its like the bloody arctic up here!
Oh no, maybe thats my right foot again

I must remove the excess ballast from the shoes.

rossd · Post by **rossd** » Thu Sep 28, 2006 10:40 am

I really don't mean to urinate on your fire.......

Diesels don't run on "choke" as petrols do.... (Idle speed is increased when cold by advancing injection timing, not increasing fuelling!) They actually run more efficiently when the air is cooler. The actual reason why you get less MPG's in winter is because around October time (eg now) winter diesel is introduced. Simply, this is normal diesel with an additive which prevents diesel "waxing" in the cold winter months. This also has the side effect of giving worse economy, as the diesel is slighlty more dilute with this additive in. (It reduces the Cetane rating a couple of points. (Cetane is for Diesel is what Octane is for Petrol)).

Also, when driving on the motorway you are bound to get less MPG's, have you ever watched the trip computer on the motorway when compared to an A-road? Mine can read a good 60mpg when on the flat and cruising at 55 - 60mph, drops to 47 at about 70 - 75mph.... (I have averaged 52mpg over 5k miles with my chipped 90 HDi

)
Food for though

Post by **Welly** » Thu Sep 28, 2006 11:39 am

You're a bit off track there chappy.

Our HDi's have a Cold Start Enrichment programme.

The HDi engine has a fuel temp sensor on the fuel rail, this measures fuel temperature and coupled with engine coolant temp and ambient air temp from the air flow meter the ECU calculates injector duration.

Engine idle speed is totally unaffected by cold starts here, the combustion process is purely based on an increased amount of fuel untill such time as coolant temperature allows a normal fuel map, luckily as the fuel is pressurised it warms up which helps the cold starts so the enrichment programme can be as short as a few minutes, the fuel itself can reach 60 deg C under pressure (hence the heat exchanger directly under the driver underneath the car) the heat exchanger allows the recirculated fuel to cool before it returns to the tank.

The 'Winter' fuel is not supplied in this country, the Diesel is the same all year round as it contains anti waxing agents all the time.

In some extreme climates like Canada they have different Diesel fuels but their winters are very harsh.

So, we all use more fuel in the winter, Petrol and Diesel alike.

Also I called it a 'choke' to aid simple understanding of the principle, Diesels don't have a throttle butterfly or choke mechanism as the intake system is more of a 'big hole' than the variable induction of a petrol.

niz406 · Post by **niz406** » Thu Sep 28, 2006 11:53 am

Thats right! Now this is getting technical....

* Sits back and enjoys the 'dirty' mans fuel debate....

chili · Post by **chili** » Thu Sep 28, 2006 7:00 pm

well rossd

we are waiting for you technical response, this is warming up

niz406 · Post by **niz406** » Thu Sep 28, 2006 8:29 pm

No Not at all..... I know bugger all about Diesels and so its interesting to me to see two great minds debate about the froggy technology! Both have rasied very good well researched points !

LXHDi110 · Post by **LXHDi110** » Thu Sep 28, 2006 9:41 pm

Just to add a note.... over the last 13000 miles i have averaged 44mpg, mostly motorway work. What i have noticed and would be interesting to see if anyone else has noticed, is.....
76l of Tesco diesel goes 50 - 75 miles less than Shell or Esso diesel.
It may be cheaper but not more cost efective.
Anyone else seen this?

turbolag · Post by **turbolag** » Thu Sep 28, 2006 10:46 pm

I've seen no difference in the colder mornings - i'm still in the 51-53 mpg range in daily motoring, and can easily eke 4 digit mileages from a tankful.

The 406 HDi holds the world endurance record for a production car on public roads. Some bloke in New Zealand managed 1900 odd km at 79 odd to the gallon, so 650 from a tank sounds a bit high. 650 miles would leave me still with a good third of a tank or more remaining on the guage. I usually refill at half on the guage, which typically equates to c.480 or so miles.

Captain Jack · Post by **Captain Jack** » Fri Sep 29, 2006 8:40 am

Don't forget that turbolag has a 90bhp version.... wouldn't that have a positive effect on ecomnomy?

mjb · Post by **mjb** » Fri Sep 29, 2006 9:17 am

LXHDi110 wrote:Just to add a note.... over the last 13000 miles i have averaged 44mpg, mostly motorway work. What i have noticed and would be interesting to see if anyone else has noticed, is.....
76l of Tesco diesel goes 50 - 75 miles less than Shell or Esso diesel.
It may be cheaper but not more cost efective.
Anyone else seen this?

I've seen the same on my petrol turbo. 34mpg on Tesco crap and 38+mpg on BP

Doing 3000 miles a month I really should be driving a diseasel shouldn't i? :/

Post by **Welly** » Fri Sep 29, 2006 10:15 am

mjb wrote:I've seen the same on my petrol turbo. 34mpg on Tesco crap and 38+mpg on BP

Doing 3000 miles a month I really should be driving a diseasel shouldn't i? :/

Well, as the american's say.......Let's do the Math

3000/38 MPG (You) = 78.94 Gallons @ say 4.36/Gallon = £344.18 (f*ck me)

3000/45 MPG (110 hdi) = 66.67 Galls @ say 4.45/gal = £296.68

344.18 - 296.68 = £47.50 saving

I have perhaps been a bit conservative with the Diesel MPG here, but if you are getting 38 MPG from your petrol you aint doing bad.

PS. anyone want to come round to mine for dinner tonight?

Post by **Welly** » Fri Sep 29, 2006 10:48 am

It was a joke, which clearly went straight over your head

I was blabbering on about boring figures, and most people would say ' I bet he's a barell of laughs at a dinner party' ....see?

Post by **Welly** » Fri Sep 29, 2006 12:02 pm

supafrisk wrote:I did wonder, seeing as the average man can't cook.........

I'll have you know my Cooking has won an award.......

The most members of one family with e-coli bacterium poisoning

406oc.co.uk

Fuel Economy Dropped

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