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S80 '98-'06 / S60 '00-'09 / V70 & XC70 '00-'07 General Forum for the P2-platform S60 / V70 / XC70 / S80 models |
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Driving styles - automatic v70Views : 1897 Replies : 42Users Viewing This Thread : |
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Dec 6th, 2017, 20:35 | #21 | ||
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Quote:
Quote:
In a coasting situation (disconnecting the engine from the wheels via clutch/neutral gear in a manual or putting auto gearbox in neutral, and then rolling along) the engine keeps using fuel because the ECU ensures it stays running at its tickover rpm. In an overrun situation (keeping the gearbox in gear, not pressing a clutch pedal down) if you let off the throttle so that the car's momentum, turning the wheels, is pushing the engine faster than the throttle wants it to go, then the ECU will cut fuel delivery to the engine for maximum engine braking and maximum fuel saving Last edited by cjard; Dec 6th, 2017 at 20:48. |
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Dec 6th, 2017, 20:51 | #22 |
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I think the notion of 'coasting' to save fuel had it's origins in the days when engines were carburettor fed, before computers assumed responsibility for engine management.
My father used to do this in his Ford Popular and encouraged me to when it was safe to do so. Then again, he'd just come through the immediate post-war period when petrol was in very short supply. Reference to 'freewheels' reminds me of the Wartburg that I owned briefly back in the '70s. That was there more in the interests of engine preservation rather than fuel economy. The engine, a 3 cylinder petroil lubricated 2-stroke, could potentially be starved of oil on a long downhill grade when on the overrun, with the attendant risk of seizure. The device, which also facilitated 'clutchless' changes, could be locked out to provide engine braking in mountainous regions. But those days are long gone! Regards, John.
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Dec 6th, 2017, 20:59 | #23 | |
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Thanks John. Regards, Andrew |
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Dec 6th, 2017, 21:30 | #24 |
Aka MadBabs
Last Online: Nov 11th, 2022 15:29
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Location: London
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And my opinion is somewhat different about that indicator..
But then, I spend quite a bit of my time in London's traffic. Nothing (not even BMW drivers) more annoying than stopping behind a car, without indicator on, at a junction, only to find out that HE IS actually turning, and begins to indicate when yellow light kicks in.. Result? Stuck behind.. |
Dec 6th, 2017, 21:40 | #25 |
Aka MadBabs
Last Online: Nov 11th, 2022 15:29
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OK, OK.. It may look different in suburban areas..
But in the middle of rush hour down here I do get proper mad at times.. |
Dec 6th, 2017, 22:48 | #26 |
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Early riser
Ah, ok, so I wrote at silly o’clock in the morning...
Towed automatics must have their wheels off the ground. As do HGVs; you’ll notice that they either disconnect the prop or pull the half shafts out of the hub as large transmissions are also lubricated by pump rather than splash. Re coasting, my text was muddled, but the point was correct; when you coast in D, the ECU recognises that fact and doesn’t fuel the engine. When you coast in N, if has to fuel the engine. Therefore coasting in D is more fuel efficient, which is perhaps counter intuitive, but accurate nonetheless. The systems used by Saab et al were nice and all that, right up until your brakes got hot and then they were less appealing. You’re right re the two stroke lunrication concern too. There’s a reason we don’t have those exact systems now.... in short, leave it to the computer, it knows what’s going on. Most of the time. Re using N or P at temporary stops isn’t actually a good idea. Wear on an auto only really happens when a clutch or a brake band engages. The more times a clutch engages, the more wear on the friction material inside and it seems silly to burden the transmission with more changes than it needs. It’s also counter to the point of an auto, where you shouldn’t have to do anything but go and stop. In the scenario I referred to, taking the car out of D won’t actually help your brakes unless you also use the parking brake and come off the service brake (assuming the off-slip is on a hill). It is true that you treat the car behind to lots of brake lights, and whilst that’s a thoughtful consideration, beware of giving mixed messages, especially with indicators. Imagine you signal left and then cancel it; how can the driver behind determine the difference between you saving his retinas and changing your mind? Signal clearly in good time and limit the changes where possible. P |
Dec 7th, 2017, 04:53 | #27 |
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So what your saying is, it’s best to keep in drive all the times and use the service brakes to stop, wait etc??
What would you do if you know your going to be stopped for say 5 mins? The usual situation when the little one wants a **** at Asda or the missis wants to check every door Is locked in the house 5 times before leaving. I hate turning the engine off and on. Best to sit with the foot on the brake or put it in Park? |
Dec 7th, 2017, 05:19 | #28 |
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If you’re going to be waiting for 5 minutes, then you’re not going to be able to creep forward for that long, of course you’d be wiser in P because that would be considered parked. But you don’t need to use P for traffic lights, slow approaches to roundabouts, that kind of thing.
(I once told my children that my wife was on “Britain’s Got Talent” as a flapper:- I would drive my car into the stage, and then shout ‘Susan, come on, hurry up’ and she would then run around the stage house, checking windows, writing 16 page missives to whomever fed out cat, washing up, changing bedsheets, choosing wallpaper etc. My children firmly believed we got to the semi final, and only failed to progress to the final because there’s a half hour time limit on all performances.) |
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Dec 7th, 2017, 09:13 | #29 |
jasmith44
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When I am waiting at traffic lights I nearly always hold it on the handbrake,i suppose it helps to keep the handbrake useable and free.
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Dec 7th, 2017, 09:59 | #30 |
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