"With stop-start system"

Well originally just the former, nowadays the latter, VW formel Es are the

It'sa define longish question, personally I still stop the engine at level crossings, but not traffic lights.

"Kostas Kavoussanakis" wrote

Where have you got that information from?

It was probably true in the bad old days of carburettors when the fuel evaporated or boiled as the heat rose into the float chamber making hot engines a nightmare to restart. This feature is now obsolete.

D you have some solid background behind your assumption or is it just folklore?

I think he's trying to say that it costs you less to run an engine for times less than 1 minute than to switch off and restart (in that the restart will burn fuel, energy from battery requiring replacement, and presumably wear and tear on starting components). Over one minute, the value of petrol saved exceeds cost of restart. Much like the myth? that leaving a flourecent tube on is better than turning it off everytime you leave the room.

In practice, you never know how long you are going to stop for - these days its probably going to be longer than you expect - so if you do it every time (bar lights you know timing of well), you may win..

Yebbut once you have bought the car with stop/start and so long as the parts last longer than your ownership there is no additional cost in using it.

... starting a flourescent seems as hit & miss as an engine with a carburettor.

Well therein lies the question - presumably such systems use identical starter motors etc as standard cars - and a starter may give up the ghost after fifteen years of use at one start per day - then at ten restarts per journey, it may only last a year and a half.

I'm sure the carburettor was a red herring introduced by the last poster. The op was not suggesting that the car would be difficult to start after a switch off, merely that doing so would burn more fuel than leaving it run - ie throttle opened wide to get it to fire.

A flourescent does need a bigger current to 'ignite' it, so there may well be truth in the rumour, much as in the rumour that leaving a traditional bulb on 24/7 is better than on/off/on/off as this blows the bulb earlier.

It would be interesting to know how long stop/start has been around and whether any studies have been done on actual savings.

Citron first came on market with start /stop, they use a alternator / starter built into the back of the flywheel. It's a bit more robust than the normal starter and produces higher output for rapid recharge.

It's normal to require fuel enrichment for hot starts, done by having a richer map or fuel adjustment in the ECU. Carbs just ran rich anyway so choke wasn't needed for hot start. I've unplugged the "hot start" solenoid on my car, it has a reputation for causing flooding. It connects the fuel pressure regulator to atmosphere instead of manifold for 3 min after/during a hot start so fuel pressure is 10psi higher at idle (but 10psi low and so dangerously lean on boost!!).

Filaments are most likely to fail on switch on. Again due to current inrush.

Google / Wiki it.

Correction. BMW ARE NOT USING THE PSA SYSTEM. I read "BMW is including the technology" and stopped. Bosch use a "enhanced" starter. It seems Bosch are really going for Lucas's crown of "Prince of Darkness".

Peter Hill gurgled happily, sounding much like they were saying:

They did this time round, but VW were doing it back in the early '80s, badged as "Formel E".

For rather less than a second.

You can try this one for yourself, it's not true either

There's a lot of studies, that's why nearly all car manufacturers are introducing it.

I don't see what that would tell you that isn't trivially derived from a test bed which gives you a much better comparison. But if you really wanted to then you can switch it off on the last BMW I drove & get a comparison. Obviously it makes sod all difference on the motorway.

unless the stops are long then the savings will be miniscule, the aggravation when it won't start will outway the savings !! Buy a modern auto stop start or a prius.

If you're going to stop the engine, then you can cut the fuel on the overun, so that wouldn't save you anything

Dunno, I'd imagine a slow crawl as that'll take less energy, but it'll depend on how slow.

It seems to vary from manufacturer to manufacturer, all the recent ones I've seen kill it by the time you've put the handbrake on & restart it as you touch the clutch.

I meant 'independent long term study' ie, we had two identical models for five years, one with stop-start, one without, this cost x, this one y.

Else I'm a bit suspicious that its just a nod to the green lobby which can produce short term 'savings' in lab conditions - much like mpg claims can be printed which can only be achieved by driving at exactly

I'm thinking real life against theoretical figures - I'm sure there are numbers out there that will 'prove' that cars halt for 1.2 mins per occaison in London traffic or somesuch, and therefore the system will save X when replicated on a test bed. However, most peoples journies are not 'average', they will optimise their route and driving style to defeat stops - coasting up to the back of queues for instance rather than arriving quickly and stopping.

With the last point it would seem that the 'way' to drive in traffic would be to screech to halt at the tail of the queue so the engine can turn off quicker - saving petrol at the expense of the braking system.

With the motorway situation, I wonder whether in slow crawl roadworks driving the optimum would be to keep crawling, or stop completely and then fill in the gap.

How long does the engine take before switching off and do you have to incite it - by saying putting handbrake on, or does it just do it immediately when mph hits zero?

conventional bulbs do last longer (more hours of light) if left switched on, switching on causes thermal shock and that is when most bulbs fail.

Which was me. I don't think it is red herring - there were fundamental issues with carbs which have gone with FI. They provide a valid background for how the folklore developed.

If it is necessary to open it up, by definition it's difficult to start. Usually necessary to blow out unburnt fuel due to flooding.

there are still a few cars that can flood themselves if stopped soon after a cold start despite fi

I did this when I was poor in the summer in a Ford Puma. I have to drive through Slough down the A4, and some lights are 4 mins+ waiting..

Driving carefully and economically, I got 39mpg. Switching the engine off at every set of lights if they had just hit red, I got it to over

Mike P