Hi All,

Last month I ordered an Octavia Elegance 1.9tdi DSG, and have been reading several threads/articles re the MPG.

At present I run a Vauxhall Omega 2.0, which is eleven years old. With is car, I have noticed, that when on the motorway at about 60 it seems she isn’t driving to her full potential. However, when she reaches about 85 (about 3000 revs) she really comes into her own. It appears she becomes quieter, smoother, and has better handling. (As if ground effect comes into play) But at that speed I get about 30ish mpg.

I like the idea of good mpg, but I also like the idea of getting to where I’m going relatively quickly.

Has anyone found an optimum speed for the 1.9Tdi and If so what mpg do you get at that speed?

Many thanks, RoystonB

My 1.9PD is most economical at 60mpg. Any more and it starts using fuel much quicker.

On a long motorway run at 60mpg, I have pushd 65 + mpg out of mine, purely by not hammering it, and using proper fuel, not supermarket stuff.

Mike

Should that be 60mph? Or do you have a magic speedo that gives you mpg instead of speed

early days with my 1.9TDI, but i'd agree 60 is a sweet spot for maximum mpg. unfortunately that is a bit slow, so i seem to do just under 70 which gets the display into the low 50s quite easily on the motorway.

Edited 11 February, 201016 yr by redlemon

The motorway mpg figure in magazines is based on 56mph I believe.

My 2.2 petrol Omega automatic estate did 40mpg at a steady 70mph on a level motorway, and dropped off slightly at above that speed. But average mpg around town and motorway was about 24 mpg. Recently doing a lot of low mileage town driving, I was only getting 17.5 mpg.

My Octy 1.9tdi manual estate does just about 60 mpg on recent crowded motorway and main road mileage, with speeds up to about 60 mph. I've noticed that it drops off seriously if I drive at 70 to 80 on the same route, so I guess the aerodynamics are not as good as the Omega. The Octy on its first 4 tankfuls has averaged about 42 mpg, which I think approximates to just over twice the mpg I was getting in the Omega doing the similar inefficient driving.

I anally record the mpg because I also drive an auto diesel Discovery. With that and the Omega, I was trying never to brake, always aiming to stick at above 50mph to lock through the auto etc etc. I've not been quite so careful with the Octy.

I get 50-60mpg out of my 1.9 105 DSG depending on usage/conditions but most of my driving is A/B roards, 60-65mph returns 55-60 mpg average, 70mph results in 50-55mpg and anything above that it does drop off a little more quickly. Keep an eye on your tyre pressures as this can make a noticeable difference and supposedly the long life service oil is supposed to give a few more miles per tank.

the optimuim speed is rubbish, its the revs that count as smaller engines will rev more at 56mph to bigger engines. Petrol cars its around 1,500-2000 rpm, and diesel cars around 2,500rpm

No, motorway figure based on 75mph, average speed on motorways throughout Europe.

Fuel figures shown by the EEC standard of 56mph (90kph) and 75mph (120kph)

That's Brussels for you!

Mike

I don't know why I wrote motorway I didn't mean it. 56mph sticks out from memory in magazines though.

Why travel at 60mph on a motorway in a car??? If you do, then I hope you use the inside lane!!

Why travel at 60mph on a motorway in a car??? If you do, then I hope you use the inside lane!!

All cars should be using the inside lane.

Not sure on the PD105, but on a PD140 if you keep the car below 2000 revs on the m/way and drive as normal on the roads you'll easily get into the 60's. 1800rpm gives about 60-65mph.

I went up the M27/M3 and into outer london and at the end of that the MPG was showing 72.8mpg and a fill up showed it wasn't far out.

Basically keep it just below where the turbo cuts in when cruising and you'll save fuel.

Thanks everyone for your replies, most interesting.

I must admit I’m a complete novice when it comes to things like Turbos.

Cheezemonkhai mentioned about keeping the revs below the Turbo kick in.

Now I understand that severe acceleration will trigger the Turbo at certain revs, but if you are cruising and relatively slowly build up to, say 70mph, does the Turbo still kick in at the same revs, or will it kick in only when there is need for that extra torque (If that’s the right word).

Lastly how will I know when the Turbo kicks in, when cruising down the M4?

Thanks again, RoystonB

Thanks everyone for your replies, most interesting.

I must admit I’m a complete novice when it comes to things like Turbos.

Cheezemonkhai mentioned about keeping the revs below the Turbo kick in.

Now I understand that severe acceleration will trigger the Turbo at certain revs, but if you are cruising and relatively slowly build up to, say 70mph, does the Turbo still kick in at the same revs, or will it kick in only when there is need for that extra torque (If that’s the right word).

Lastly how will I know when the Turbo kicks in, when cruising down the M4?

Thanks again, RoystonB

If you like plodding along then retrofit cruise control. This will help with mpg.

All cars should be using the inside lane.

Except me because I'll be overtaking them

Edited 11 February, 201016 yr by Raglits

Well although I have a petrol definitely keep it between 55-65mph. Did a journey recently to galway mostly National or A road for those unfamiliar and passing through a few towns. Average a not too shabby 43.6mpg quoted on the computer for 410mile round trip in a 1.4 estate, however goin along literally a few miles of the m18 at 90-100mph needless to say sucked alot of fuel went down into the mid teens. Use your big toe for the accelarator and you cant go wrong.

If i set the cruise at 80mph on a decent trip my car will do 46mpg (based on fill to fill not mfd nonsense) good mpg readings come from throttle positions rather than speed ie floor it to 60 may well be worse than working slowly up to 80mph

I think one of the main contribution of fuel consumption on motoways is from drag force. The drag force is usually calculated as the follows:

F = 2*p*S*Cd*V(2).

F - drag force

p - is tne projectol area of a car on the direction of driving

s - air desity

Cd - Drag coefficient

generally p,s and Cd are treated as constant for a given car.

So the drag force a given car need to overcome at a certain speed goes up exponentially with the speed.

sorry for getting those math stuff out...

Indeed, however different engines are most efficient at varying revs, and gearing will give different optimum speeds for differing vehicles. As a rule of thumb, the faster you go the less mpg will be returned, but if the car is more efficient at higher rpm, or driving faster allows a higher gear to be used, optimum speeds could be higher.