Hopefully this isn’t in the wrong forum, I’m looking for a factual answer.
I just got a new car (Infiniti Q50) that features the idle start/stop feature. I’m wondering if it is operating as designed, and if so, who designed this dang thing?
So, the engine stops on idle, usually shortly after pressing the brake. Sometimes not immediately. However, I expected it to stay idling until I moved my foot off the brake. But no, it starts up unfailingly after about 15-20 seconds, even when I am sure I haven’t moved my foot.
I did a test letting it idle in park, with my foot off the brake. The engine ran as normal for 30 seconds, then switched off for about 15, and then switched on again. It did this repeatedly while idling. It appears to be on a cycle where it stops for maximum 15 seconds and then switches on whether I need it or not.
Normally at a stoplight, I stop for more than 15 seconds. I’m wondering whether this is really saving any fuel or carbon emissions, as I suspect restarting it uses more fuel than was saved while off for 15 seconds.
On a direct injected engine that’s already warmed up, restart won’t waste gas. The engine restarts on its own after 30 seconds for a short time to keep the catalytic converters hot (reduce emissions). If you do a lot of start/stop driving like rush hour commute, EPA testing shows a 1 to 2 mpg improvement in emission/mileage testing. Real world, who knows?
Here’s a real world test. YMMV
Just a guess - If you have the air conditioning on, the engine may need to start to run the air conditioning compressor. If you don’t have the air conditioning (or heat) on, the start/stop would probably only restart the car when you took your foot off the brake, as you expect. What does your owner’s manual say about the feature?
yes, it sounds normal. auto stop/start won’t keep the engine off indefinitely at a stop. it’ll start the engine back up if it needs to, e.g. if the climate control demands it, or to keep the catalyst from cooling too much.
My Ford has this feature and whenever I stop, the heater/cooling fan slows right to conserve power. With petrol at not far short of £5 per gallon, it does help.
One thing that article doesn’t mention is that the system is disabled if the battery voltage drops below a set level.
The owners manual says very little from what I’ve seen. I’ll have to dive back in I guess. The fan seems unable to turn off, although I could see what happens with shutting the AC off.
Good points all. Fighting ignorance and all that. Thanks
One comment I make about a lot of these sorts of computer-controlled things, from thermostats to cars to phones to …
Unlike the Olden Dayes (e.g. 1970s) of control systems consisting of a couple relays & toggle switches, a modern device, even a cheap one, can make its decisions based on dozens of input variables. Some of which inputs you may not be able to see in any way. As such, trying to divine it’s “thought process” from watching it work is a fool’s game. At best it’ll seem unpredictable; at worst it’ll seem random and capricious.
Ideally the manufacturer would provide complete documentation of the logic used. The only alternative is for the user to assume A) it’s working right, and B) smarter people than you have decided how it’s supposed to behave. Your job is just to accept it and put up with its idiosyncrasies. Just as you would with a cat or a spouse; change is not possible and resistance is futile.
I wish it wasn’t so, but I believe it is so.
[After 4 years I finally deduced all 6 variables that control the behavior of the door lock/unlock pushbutton inside my car. And that was a 2003 model. I shudder to think how smart (read as “stupid and capricious”) that button will be in my next car.]
I’ve never heard of this feature. What if during this idle/engine shut off, I notice some sort of an emergency situation requiring immediate acceleration? Do I have to wait for the engine to start? This sounds like a safety hazard.
Also, doesn’t this kill the battery? Especially if it’s cold, and you just started the car for the first time, then immediately drive locally with lots of stops from traffic, stop signs, and red lights.
The engine starts when you press the accelerator. It’s absolutely seamless.
It’s analogous to hybrid engines that switch from gas to electric and back as needed from moment to moment. Modern computer controlled engines calibrate the world in milliseconds. By the time you would notice the change it’s already happened.
Several of the “luxury” brands have this feature and have had for years. They all promote it as higher fuel mileage, so when the OP wonders “whether this is really saving any fuel or carbon emissions” you have to wonder yourself what he was thinking. Who would go to the fantastic extra R&D time and expense to install a more complicated engine in a luxury car specially to gain MPG because hybrids are hurting sales and end up using “more fuel than was saved while off for 15 seconds.” Seriously, who would do this? Who would even think this?
I was using a memory from my test drives two years ago, so I should have double-checked. But my point stands either way. There is no waiting for the engine.
That is a good question. Several times in my life I have discovered a bad battery, get a jump from the neighbor, drive to AutoZone, buy a battery, get a jump and drive home and put it in.
If I had one of these new cars, would the car die at the first stop light?
I can see starter motors and batteries wearing out much sooner with this technology. I wonder what the cost analysis is, comparing fuel savings vs parts replacement.
Me, defend the auto industry? Not likely. The auto industry is full of miraculous new technologies that fail to live up to their promises. I once bought a VW diesel. No, not the current ones. The ones in the 1980s whose engines blew up. (It happened between the time we ordered our new non-VW car and the time it was delivered. Try getting a dealer to believe that.)
But this was not a good question. And neither were some of the later doubters. The OP is like one of those science threads in which the poster asks whether scientists forgot something that would almost literally be the first question the scientists asked themselves. If this is the first question you come up with when hearing about stop and start engines, the answer is they already thought of that.
The fan seems unable to turn off, although I could see what happens with shutting the AC off.