Some valid points except for the start/stop being irrelevant - how many owners would pull into a service area after hard motorway use and have the S/S system cut the engine the instant they pull into a parking space?
General TwinAir Thread (including MPG)
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General TwinAir Thread (including MPG)
Some valid points except for the start/stop being irrelevant - how many owners would pull into a service area after hard motorway use and have the S/S system cut the engine the instant they pull into a parking space?
Surely after a "hard" drive on the motorway. The slip road off, then the crawl to a parking space will be enough time for a modern turbo?
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ahmett
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Thats not good at all my 1.4 does that! Its not like the ypsilon is that heavy either! how many kgs? i would assume my fiat 500 with all the extras to be about 1050 kgs.
Yes, our Subaru has done 220k miles plus and its done a lot of motorway miles and pulled off into services and not been idled before being turned off and the turbo is just fine. Remember this is a car from the early 90's and has probably been run on mineral oil and semi-synth.
Whilst I'm not going to disagree that it would be best that you idle a turbo engine for a little while, I really don't think that driving at 70 on the motorway and coasting into a services and then switching off is going to cause any real damage.
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Here is an ignorant question. Will a turbo necessarily have been spinning if someone is driving at 70 on the motorway? If so, is a turbo simply either "on" or "off", or will it be working less hard than if the car was being driven on a track, or significantly faster, for example?
I've always thought that motorway miles driven at sensible speeds are about the least stressful thing for a car. But I hadn't thought about a turbo.
I've always thought that motorway miles driven at sensible speeds are about the least stressful thing for a car. But I hadn't thought about a turbo.
it will be spinning fairly fast yes, but turbo's don't really get stressed by high revs.
TrevC
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Robin, as Maxi says the turbo will be spinning - the impeller sits in the exhaust flow so it will spin as long as the engine is running. It just spins faster at wider throttle openings, which makes the compressor half spin faster, giving more boost.
Bgunn, in answer to your earlier query, my precautionary turbo change was due to the wastegate linkage issue.
I can't match Maxi's turbo experience, but we've just sold our other car, a Renault with the 1.2 TCE engine. No special precautions were taken and the turbo was still fine at 34000 miles. I know this isn't much, but I honestly don't think it's a problem these days, with modern materials and oils, and most manufacturers with decades of turbo experience.
Bgunn, in answer to your earlier query, my precautionary turbo change was due to the wastegate linkage issue.
I can't match Maxi's turbo experience, but we've just sold our other car, a Renault with the 1.2 TCE engine. No special precautions were taken and the turbo was still fine at 34000 miles. I know this isn't much, but I honestly don't think it's a problem these days, with modern materials and oils, and most manufacturers with decades of turbo experience.
ahmett
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Yes but maxi, i wouldnt call cruising at 70 mph on the motorway hard driving! Thats 'cruising'. I think the idling or driving slowly after heavy use concerns driving near the rev limiter at all times. So unless you were in 3rd gear at 70mph the whole time, no worries.
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Yes, but they're what you'd call a 'mechanically unsympathetic' owner. It's no different to an older car either, you power into the services, pull up to the parking space, and shut the engine off by the ignition key. If you're going to abuse your car and the engine in it, you will either way.
Most people will slow down as they approach the service area, and then there'll be at least 1/4 of a mile of driving at below 45mph - plenty enough time to allow the turbine to spool down, and get a good supply of oil before drawing to a halt.
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It's high load, rather than necessarily high revs that generates high exhaust velocity and thus high turbine speed/high boost pressure. I.e. large throttle openings. Sitting at high revs with the throttle shut won't spin up a turbo. Which is why revving the engine when stationary won't really generate much boost.
Missing the point I was originally trying to make, the start/stop system ensures even a mechanically sympathetic owner, if he/she forgets to disable it, could automatically become mechanically unsympathetic thanks to the way it works.
I'd agree with your original point, though I'd also add that forgetting to disable S/S in such a situation constitutes driving in a mechanically unsympathetic way.
Turbocharged engines need a minimum of 3-5 mins at idle rpm before shutting down & it's the driver's responsibility to operate the car in such a way that this happens.
That said, I'd say fitting S/S to a turbocharged engine without also installing some form of automatic thermal protection constitutes poor design.
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I think I read somewhere that this is one of the parameters taken into consideration with the S&S software, along with the battery charge, A/C on, engine temperature, lights, wipers and a whole host of others.
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That's as maybe, but think of the thousands of Merc sprinter and Transit vans with turbo diesels that are *thrashed* within an inch of their lives, pulled into services and stopped while white van man runs into the service area for a p***, and they function perfectly happily.
Modern oils, coupled with turbo design, and general over-engineering means it's not really the problem the pernickety of us make it out to be. I don't deny that I take *extra* care over my car, but that's because I do anyway. But they survive quite happily given the circumstances.
OP
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Maybe this is why the A500 doesn't come with S&S.
No it's because it's more fun to sit at the lights revving it!
Well my avg mpg has now dropped under 30mpg and doing 70mph on the motorway returns 35-40mpg. Bored of this now, 3000 miles on the car it should be getting better not worse. Booked in for testing on the 30th to see if anything is wrong. Old Stilo gave me 60mpg at 70mph. Will update with results.
Under 30mpg looks odd to me I got a lot better than this with my earlier TA Lounge. Needs a check out
TrevC
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Yes, on motorway runs I get 48mpg at a steady 70.
