V90 D4 MPG Improvement

[taylora]

I think quite a few cars have coasting now (I'm sure some Audis do it too) so there must be something in it that's advantageous compared to over-run.

On the odd occasion I have used ECO mode and go down the big hill on the M77 into Glasgow, trip MPG improves more with coasting than with over run. I do end up coasting along to almost 80 at the bottom of the hill in a 50 limit though!

[Quacker]

Originally Posted by MOzS90

Why do Volvo add the coasting feature to eco mode if it makes it less eco then quacker? Maybe you should contact them and let them know you can improve their cars?

Because it impresses people who want to believe they are saving money and the ‘environment ‘. In that regard, it works.
Up until relatively recently, coasting was very much frowned upon by the UK’s Highway Code because it apparently lost driver control. This was equally spurious and based on no evidence. Coasting by knocking a manual gearbox out of gear down hill used to be very advantageous on, for instance, a three speed Zephyr6 with massive engine braking and low gearing and a carburettor that sucked fuel in even when on the over-run. In those days there really was a substantial advantage to be gained from coasting out of gear, and yet...

Fact is, you just cannot improve on using zero fuel which is the amount used on over.run. Coasting actually uses fuel to maintain engine idle speed at idle. Not much but enough to otherwise justify fitting start-stop systems to prevent idleing when at a standstill.

[elotro]

Originally Posted by Quacker

Because it impresses people who want to believe they are saving money and the ‘environment ‘. In that regard, it works.
Up until relatively recently, coasting was very much frowned upon by the UK’s Highway Code because it apparently lost driver control. This was equally spurious and based on no evidence. Coasting by knocking a manual gearbox out of gear down hill used to be very advantageous on, for instance, a three speed Zephyr6 with massive engine braking and low gearing and a carburettor that sucked fuel in even when on the over-run. In those days there really was a substantial advantage to be gained from coasting out of gear, and yet...

Fact is, you just cannot improve on using zero fuel which is the amount used on over.run. Coasting actually uses fuel to maintain engine idle speed at idle. Not much but enough to otherwise justify fitting start-stop systems to prevent idleing when at a standstill.

The key is that with over-run the speed decreases while with coasting it even increases so you can go on for a longer distance. Even do there is a small fuel consumption, it allows you to go further. I have checked this on my car and it is true but ovbiously if you don´t take in count that extra distance that you can coast, there is no gain.

[taylora]

An article explaining coasting mode and possible advantages...

https://www.pistonheads.com/news/ph-...explains/39081

[Quacker]

Originally Posted by taylora

An article explaining coasting mode and possible advantages...

https://www.pistonheads.com/news/ph-...explains/39081

Engine off coasting would indeed yield a tiny benefit. However considering the overdrive gearing of seventh and eighth gear, there is hardly any engine braking that makes any significant difference to distance travelled whether coasting or on the over-run. Coasting in Volvo doesn't work under 40mph after all.

[taylora]

Originally Posted by Quacker

considering the overdrive gearing of seventh and eighth gear, there is hardly any engine braking that makes any significant difference to distance travelled whether coasting or on the over-run.

Eh....fuel-cut off on over-run usually doesn't happen at lower rpms? So coasting (engine off or on) would indeed be more fuel efficient when engine revs in seventh and eighth gears are so low that it can't cut off fuel supply.

Anyways, I'm sure you're right and Volvo, Audi, VW, BMW, Mini, ZF, etc...all wrong.

[James77]

Originally Posted by volvocat

...and you’re driving what, exactly...?!

Hmmm, I thought I had successfully updated this with car details, apparently not.

There's only one engine that returns that sort of mileage in the range, T5 currently, I suspect T6 will be a tad worse.

I don't care about fuel, you run out you fill up what's the problem. Over the period of ownership the fuel savings on diesel/vs petrol aren’t going to change your life!

[anotherv60]

Originally Posted by Quacker

Coasting in Volvo doesn't work under 40mph after all.

Quaker your correct but it is possible to coast before 40mph for instance, If your at or above 40 mph, it will let you coast down to 30mph before coasting is stopped.

For those interested after 13,000 miles the average mpg is 47.1. Winter really reduces fuel consumption regardless of driving mode. Having spent along time driving in eco you really notice the responsiveness of the car in comfort or dynamic. I wouldn’t be able to put a number on how much more fuel efficient eco is but it does feel like it should save some fuel, ie reduced air con, lower acceleration etc.

[Fursty Ferret]

Originally Posted by anotherv60

Quaker your correct but it is possible to coast before 40mph for instance, If your at or above 40 mph, it will let you coast down to 30mph before coasting is stopped.

For those interested after 13,000 miles the average mpg is 47.1. Winter really reduces fuel consumption regardless of driving mode. Having spent along time driving in eco you really notice the responsiveness of the car in comfort or dynamic. I wouldn’t be able to put a number on how much more fuel efficient eco is but it does feel like it should save some fuel, ie reduced air con, lower acceleration etc.

If it didn’t save fuel Volvo wouldn’t do it.

[Quacker]

Originally Posted by Fursty Ferret

If it didn’t save fuel Volvo wouldn’t do it.

Really? Start-Stop saves most people about two litres of fuel a year, yet they fit it and make us pay hundreds for it.

Believe what you like, but I've given you facts. I know how this stuff works, and what doesn't.

It's all in the marketing of the feel-good factor. What really makes a difference apart from the right and left feet [in that order], are the efficiency of the engine and transmission, the gearing, aerodynamics and the weight of the vehicle. Most of the rest is just fluff.