PeteMorris Posted November 12, 2012 Share Posted November 12, 2012 In my younger days, I occasionally switched off my car engine to save fuel (so I thought), for instance if I was waiting at roadwork type traffic lights, which seemed to take forever to change. But I was told, it takes more fuel to actually start an engine, then to just have it idling for a few minutes. Now it seems with modern car technology, the manufacturers claim something like 10% reduction in fuel using this technology. I know there are various systems in use, the most efficient one (from what I've read) senses the piston positions and ignites the one(s) primed with petrol, and restarts the engine that way. Others actually use a starter motor of some sort. I have to hold my hands up, and admit, I really don't know an awful lot about this, which is why I'm posting here. So please don't rant at me. Was I mis-informed all those years ago? I have a car which does not have this technology. Is it wise to switch off when stuck at lights for prolonged periods (obviously not when electrical power is required..ie at night)? Link to comment Share on other sites More sharing options...
truman Posted November 12, 2012 Share Posted November 12, 2012 I have a Focus with start stop..it stops when you idle at a junction in neutral with the clutch out..as soon as you dip the clutch it starts almost instantaneously..I can't belive that that will use more fuel than you would if you left it idling for a couple of minutes.. Link to comment Share on other sites More sharing options...
Cyclone Posted November 12, 2012 Share Posted November 12, 2012 If you know you're going to be stationary for a long time, then yes it probably does. But the old advice about it using some fuel to start was correct, so for short stops, ie in traffic, it probably isn't worth it. (With a car that doesn't have start/stop). Edit - having been reading about this, the extra fuel usage would apply to pre ECU, non injection engines. But a car equipped with start/stop has other changes, they only do it in a clever way (depending on load/temp/driving style, etc...) they have uprated components (starter, alternator and battery) they may have a special combined alternator/starter for the hot start, etc... Link to comment Share on other sites More sharing options...
PeteMorris Posted November 12, 2012 Author Share Posted November 12, 2012 I have a Focus with start stop..it stops when you idle at a junction in neutral with the clutch out..as soon as you dip the clutch it starts almost instantaneously..I can't belive that that will use more fuel than you would if you left it idling for a couple of minutes.. I can't argue with the current tech being more efficient, cos it obviously is. If the 'old' advice was correct, I just wonder why it's not the case now? The drive train and the way an engine works is intrinsically the same as it always was (ie petrol being ignited forcing pistons up and down - Simplistic I know), it's the electronics that are clever these days. Link to comment Share on other sites More sharing options...
Obelix Posted November 12, 2012 Share Posted November 12, 2012 It's always been the case that stopping a car from idling will save fuel, even allowing for the restart. However doing this is rather bad for the engine, as almost all engine wear occurs at startup as there is no oil pressure to the bearings. This problem has been alleviated somewhat with better bearing materials but it's still there, and I wouldnt run the risk of constant stop-starting, I'll pay the small amount extra for the fuel costs and save on engine wear myself. Link to comment Share on other sites More sharing options...
truman Posted November 12, 2012 Share Posted November 12, 2012 I think the fuel injection systems on both petrol and diesel engines are much more refined nowadays..It may be that that makes the difference.. Link to comment Share on other sites More sharing options...
truman Posted November 12, 2012 Share Posted November 12, 2012 It's always been the case that stopping a car from idling will save fuel, even allowing for the restart. However doing this is rather bad for the engine, as almost all engine wear occurs at startup as there is no oil pressure to the bearings. This problem has been alleviated somewhat with better bearing materials but it's still there, and I wouldnt run the risk of constant stop-starting, I'll pay the small amount extra for the fuel costs and save on engine wear myself. When I change my car in a couple of years,it'll have about 130k miles on it..I'll let you know how it gets on... Link to comment Share on other sites More sharing options...
Obelix Posted November 12, 2012 Share Posted November 12, 2012 When I change my car in a couple of years,it'll have about 130k miles on it..I'll let you know how it gets on... Hardly run in that..:-) I tend to aim for a half million or so myself. I don't change cars very often as a result.... Link to comment Share on other sites More sharing options...
Garbo Posted November 12, 2012 Share Posted November 12, 2012 well, new engines are a lot more efficient. but the biggest change that has allowed this fairly old technology to work is the car batteries. cars with stop start will have a gel battery which is designed to operate the starter motor repeatedly without going flat and wearing out the battery. they also have different starter motors, to handle the hugely increased usage. start stop is inhibited when the engine is too cold, you need air conditioning, or heating, or the electrical load is high, heated seats, windows etc. so, dont do it in your normal car. Link to comment Share on other sites More sharing options...
PeteMorris Posted November 12, 2012 Author Share Posted November 12, 2012 It's always been the case that stopping a car from idling will save fuel, even allowing for the restart. However doing this is rather bad for the engine, as almost all engine wear occurs at startup as there is no oil pressure to the bearings. This problem has been alleviated somewhat with better bearing materials but it's still there, and I wouldnt run the risk of constant stop-starting, I'll pay the small amount extra for the fuel costs and save on engine wear myself. So you're saying that the 'old' advice was wrong? I hold my hands up, I don't know! I always thought that the problem with oil pressure was more to do with cold starting, rather than when the engine is hot? Link to comment Share on other sites More sharing options...
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