With all the car questions lately, I am curious what others think.
Remember the saying, “Starting your engine is a terrible thing to do.”?
The set up: Hot day, slow traffic, A/C on high and traffic lights long. Some people will stop their engines and then restart in 30 - 90 seconds. Fuel savings? Save wear and tear?
I kick automatic transmissions into neutral a lot and manual ones even quicker at stops but due to being taught in the olden days that the lack of oil pressure during starts, wear and tear on the starter, battery drain, and initial rich mixture during starts, that doing this as a habit was counter productive.
Now I hear that some hybrids do this a lot so I hope they are addressing the lack of oil pressure at start in some way.
What has the latest tech done that might make this an ok thing to do?
There’s a big difference between starting a cold engine, which is subject to the problems you mention, and starting one that’s warmed up, which is only subject to the starter/battery/alternator wear involved. It’s not really going to hurt the engine itself to turn it off and then restart it.
Starting a car takes as much gasoline as idling for four seconds. If you’re sitting at a thirty-second traffic light multiple times daily, that becomes a significant savings.
Stop-and-start systems have been around for some time but since the reduction in fuel consumption is small, car mfgs. didn’t bother integrating it on a mass production car.
AFAIK, The first production car that came with a stop-and-start system was the 1999 Volkswagen Lupo 3L TDI, a car that could consume less than 3 litres of fuel per 100km (more than 78mpg)!
Nowadays that gasoline is so expensive, Stop-and-Start made a reappearance in the Citroen C3 Stop&Start. Citroen claims up to 10% fuel savings compared to a standard C3.
To answer the OP: I don’t believe it is a good idea to stop and start the engine on a car that wasn’t designed with that in mind. For example, the Citroen C3 has temperature sensors on the battery and the starter/alternator. If one of those overheats, the ECU automaticaly disables the stop-and-start system until the temperature drops.
Another issue is the brake servo. With the engine turned off you can use the brake pedal only once or twice. After that the brake pedal becomes too stiff and it is next to impossible to stop the car. The C3 has a pressure sensor on the brake servo. If there’s no underpressure left in the servo, the ECU turns the engine on to assist braking.