MPG drops like a stone

Personally I find it hard to believe that anyone can be so "cackfooted" that a change in shoes would make such a big difference.

You'd have to ignore *all* the feedback you get from pressing the throttle to make such a difference I reckon.

What were you wearing, deep sea divers boots?

Tim

I'm doing better by about 2mpg since I stopped wearing toe protection shoes to work. Or it may just be that the car needs less time on rich mixture during summer.

Yes and surely, with a *modern* diesel, the ECU just wouldn't let you waste fuel, it will only take what it can burn if you put your foot to the floor.

IME that is not correct. The engines output will vary if the accelerater is pushed down too hard. Of course the driver will then have to apply the brakes to decrease speed. Unless you are at a constant speed the cpu/ecu wouldn't have a clue of the drivers intentions. Turning cruise control on seems to make MPG worse too.

When we first got the 2L Sierra Estate it was the first car I'd had with a 5 speed gearbox. On top if that, all the gears seemed pretty 'long', especially after the 1.6 Mk5 Cortina Estate the Sierra replaced.

We were towing the sailing dinghy up to the lake district and I felt that trying to use 5th when being stuck at 50 or 60 mph meant that I couldn't 'feel' any over throttling and I could often lift my foot a long way before it started to lose speed.

So, I kept it in 4th (except on the straight / flat / downhill and in a 60 limit) and it was both easier to drive and returned a better mpg. ;-)

Cheers, T i m

And were you previously getting 40mpg on runs down to Bristol ?

Cruise control on a manual car is a pretty silly idea. As to not using top when towing: certainly you should always use the gear appropriate to the load and conditions and for as long as needed, this bizarre idea that you must change up as early as possible no matter what, is a really silly one promulgated by stupid people (unfortunately often by driving instructors) along with changing down (or up) using every gear every time.

MrCheerful formulated the question :

Sorry, I cannot agree. My present car is a manual, the one before it an auto, the one before that a manual. All three had cruise and I find cruise very useful indeed, even on the manuals for holding my speed steady. I am perhaps biased, in that I have always had cars with plenty of torque?

I did think they had changed driving instruction, so they don't sequence down through the gears?

I have only played with one manual with cruise: a 2litre Honda civic, I am sure it would be ok on a level motorway with little traffic, but was not good on anything else. With an auto you can just flick cruise off if you are gently slowing and when you turn it back on it will pick whatever gear is needed to resume, rather than you having to stir things to get going again.

I hope that driving instruction has improved in recent years, it used to be abysmal.

I've had cruise control on a Vectra and Skoda, both manual diesels. Both behaved as you describe for an auto, within the limits of not needing to change gear. Where I need to slow more, I doubt that it would have been appropriate to use it anyway.

I appreciated two factors:

1. I was far less likely to exceed the speed limit.
2. I am less likely to get cramp in my right leg on a long journey since it is relaxed rather than slightly tense all the time.

Yes - agreed - especially on speed limited sections of motorways, around roadworks. My new car doesn't have cruise control and I miss it more than I expected.

OK specs is a pain but is cruise control speed correct or just as far off as the speedo? 53mph indicated is GPS 50mph, indicated 50mph is around 49mph on one car I use. Others can be as far off as doing 45mph at indicted 50mph. On "smart" M-way they use fixed cameras with variable speed activation that only work when the limit is set. But they are now sneaking fixed cameras in mounted on side platforms that are on all the time.

My experience is that cruise control holds the speed at which it is activated. So on a 70 mph motorway I drive at an indicated 70 and push the button - the car then holds the indicated 70.

I checked it against the average reported by my satnav - only really possible with the cruise control holding the car's speed steady - and the satnav reports 66 mph. It is said that many speedos over-estimate by a few percent.

Cruise control will just hold a constant speed. Accuracy is variable. It's generally *exactly* as far off as your speedo is if it's dependant on pulse counting.

As you've found, using GPS to check is the only way.

Tim

Nope. Not as useful as on an auto but I've had it on plenty of manual cars and wouldn't be without it (going back to my first vacuum powered unit fitted to and old Volvo 245 estate).

I really wasn't keen on the way that my wife's manual golf *doesnt* drop out of cruise control when you change gear but having got used to it, I prefer it to ones that I have to reset every time I change gear between 5th & 6th (in either direction).

Tim

Cruise controls slows the car as well as speeds it up to keep the speed constant. = Wasted energy = Lower MPG

Um, not generally. The majority of CCs *only* control the throttle, not the brakes. Full adaptive cruise control a la VW will apply the brakes but that's far from being the norm.

The function of CC is to maintain constant speed, not to optimise MPG. For some drivers and journeys CC might be more economical, but that's not its function, that's a happy accident if it occurs.

Tim

It is quite exciting when adaptive cruise control decides that a bend with signs is a stationary vehicle and hits the brakes for you.

If you the driver try to maintain a constant speed you will probably do exactly as the CC does - less throttle to slow down, more to speed up. However you have the advantage of anticipation - so ...

- if there is congestion ahead you might slow down earlier by lifting off the throttle, whereas the CC would hold the speed until you found it necesary to disengage it or brake - so using more fuel;

- if the road goes down a hill then up you might maintain a constant throttle position so the car speeds up then slows - which might (or might not) use less fuel than CC.