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I'm driving a 1.4 TDI and I'm not getting anywhere near the official fuel comsumption figures! Could it be the trip computer? around town I get between 35 to 37mpg, and on a long motorway journeys without the aircon on at a steady 65mph, I'm getting just about 50mpg! There's no smoking on the motorway, but just a little on urban journeys when I pull away! I thought PD's don't smoke! any suggestions?

Maybe just a glitch on the trip computer goosey, i get between 52-55mpg about 70mph on the motorway, and the black smoke is normal "i hope" lol, cos if i pull away hard i get it on mine so no need to worry
Dazza

I wouldn't worry about the black smoke it's normal for a diesel. 35-37mpg around town is about right I get roughly the same, try to drive in higher gears it will improve your fuel economy

Cheers guys.... my old man told me that your optimum full efficiency is when your rpm hits its max torque...so I think on the 1.4TDI that's about 2,200 @ 75bhp which equates to about 65mph. So that's the most econimical speed...hmmm far too technical for me!

my 1.4 tdi pd has never smoked under hard acceleration, neither did my dads old 1.9tdi pd 130. Think its gifferent from car to car. also on motorway journeys my car can gain high 60's.

someone remind me, are diesels most efficient at full (or at least, wide/near-full) throttle, or when cruising with nearly closed throttle? Can't remember which.

if anyone knows which it is for petrols that'd also be a boon.

(and whether, for either/both, its better economy-wise to accelerate gently in a lower gear, or with more throttle in a higher gear, getting the same thrust. stuff i've seen e.g. on hybrid owners forums suggests the latter)

Tahrey1043 wrote:someone remind me, are diesels most efficient at full (or at least, wide/near-full) throttle, or when cruising with nearly closed throttle? Can't remember which.

if anyone knows which it is for petrols that'd also be a boon.

(and whether, for either/both, its better economy-wise to accelerate gently in a lower gear, or with more throttle in a higher gear, getting the same thrust. stuff i've seen e.g. on hybrid owners forums suggests the latter)

Any car is more efficient on fuel when you dont put your foot down much and yes driving in higher gears is more efficient also

I don't mean flooring it at high revs, more giving it like 2/3rds to 4/5ths gas lower down around / below the torque peak...

Apparently this gives better economy because of less throttle losses or something...???

(doesn't seem to have worked brilliantly for the Astra... but it's hard to tell as it's economy doesn't seem to follow a sensible pattern)

My trip tells me that overall on average i get 42mpg.

hmmm, interesting PDF I ran across about a week ago (dunno if i saved it, im afraid - think it was a rando-accidental thing that popped up whilst looking for work stuff at college) from a VW report on fuel economy and emissions. Think it was an internal thing regarding their attempts to get into line with the latest extra-stringent european regulations. The thing that I took away from it was pretty much that the lower the rpm's you can achieve at a certain steady speed on a particular engine, the lower your consumption is, without exception (at least insofar as the diesel was concerned)... interesting. Wonder if it's true.

(they were comparing various manual gearboxes and automatic shift patterns on passat TDi's or something - including getting 6th gear at about 35mph and 1000rpm, which was probably something carried over into that Audi A8 TDi on top gear. also they subtly dissed the european standard test procedure for having set speeds for gearchanges on the test "route" on their dyno - not getting 4th til 40mph, etc, totally skewing their attempts at fooling automatic drivers to save diesel )

there may be some weight to the argument ... i remember my old boss at the nightclub mentioning something to me (when i complained about the astra's drink problem) along the lines that i might be as well to buy a brand new Scania truck tractor-unit. apparently their most modern diesel engine and transmission pulls all of 1100rpm at 55mph cruise and delivers over 45mpg on the flat with a load on.... sure, even the vaux should be able to manage that under the same circumstances, but it's hellishly impressive when you consider the sheer aerodynamic cross section of the thing, friction area of the power unit/mass of the pistons, and the rolling resistance on it's tyres.

PS what about the new "german built" (VW, hm?) economy-supercar that some of you may have seen in the newspaper.... 2-cylinder turbodiesel (sound familiar? possibly supercharged instead?), hybridised, in a lightweight carbon / plastic shell (similar to the "1L") weighing all of 450kg and very streamlined, but capable of carrying four and a half adults plus bags up to the ton, and getting over 180mpg on a cruise. Nice.