I recently had the opportunity to drive a car with these new auto-start/auto-stop engines. You know the type. You are standing next to an idling car, and suddenly the engine stops. In the old days, we called it a stall, but new engines are doing it for fuel savings and saving the environment. I am all for protecting the environment, but I am not a huge fan of these engines. Let me explain.
These were first seen in high-end Mercedes and BMW cars. Today, they are everywhere that is not a hybrid. The idea, as I said, is to reduce carbon emissions while at idle, something most cars do a lot of in urban environments. Idling creates a lot of carbon because the gas does not fully combust, unlike when the vehicle is in motion (not entirely sure why) and it also creates a pocket of concentrated CO2 gas, along with some other not so healthy gases. So anything that makes idling cleaner is a good thing.
The problem comes about when you need to actually get going again. Because the engine actually stops, there is a brief delay before it gets started again. This is a bad thing in certain situations.
For example, if you are anything but number one in line, the delay in getting the engine started, and the gears engaged (all of which is automatic) is not a big deal. The three or four-tenths of a second it takes is manageable and usually is accounted for by the car in the number one slot getting his vehicle moving. Not a big deal.
However, if you are in the number one slot, and the car behind you is not suffering from waiting for his engine to start, you are going to get honked at, at the very least. I had a couple of near collisions simply because it took that much longer to get the car moving off the line when the light turned green.
The second issue is safety. I was taught, when I learned to drive a stick shift, that you never ride the clutch. The engine should be engaged at all times. The problem is that the sensor that puts the engine to sleep when you are idling at a traffic light does not know the difference between idling at a traffic light and waiting to make a left-hand turn. I had the engine cut out just as I had an opening to make a turn and missed the opportunity because the engine was off and had to restart. Fortunately, there was no one behind me trying to make the light as well. This is not safe. The same is true with stop and go driving. I had the engine shut off just as I went to touch the accelerator.
Finally, a minor note. The engine shutting off also shuts off the air conditioner. It will kick back on, but I can see where hot climates will result in higher in-cabin temperatures, especially in stop and go driving, where the engine shutting off actually makes it more uncomfortable inside for the passengers. Again, I cannot see this as a win.
I am sure someone has done the math, and everyone is perfectly happy with the reduced emissions, while the safety issues are perceived as minor. As a driver, I do not find that these sorts of engines are good, or safe. Time will tell.