Dear Car Talk:

Here's an item that I think would interest many of your readers. I have a 2019 Buick Enclave. One of its many features is the automatic engine shutoff when I stop. It's not something I love, but I eventually got used to it.

Yesterday I came across a discussion on Facebook, and there were literally hundreds of rants about why it was no good. "It doesn't save gas," "It will require replacement of starters and associated parts," "It's bad for the battery," etc.

Many mentioned the lack of heat or air conditioning while stopped, although mine starts back up if needed. Others mentioned holding up traffic while you restart, which, of course, is not true.

So, is this a gimmick, or does it really save gas? -- Tom



Ah, I see the Russian trolls are using Facebook to try to divide the American people over important issues again.

It does save some gas, Tom. Studies show it improves fuel economy by a few percentage points. That makes sense, right?

Let's say you're stopped at a light or in traffic about 3%-5% of the time you're driving -- now you're not using any gas during those stops. You're also not putting any wear and tear on your engine, which is nice. More importantly, you're not creating any air pollution. And if we're collectively cutting vehicle pollution by 3-5%, that's a pretty big win for everybody.

These systems have been around for five to 10 years now, and we haven't seen any increase in starter or battery replacements yet. It could happen, but we've seen nothing to suggest it yet. And because warm engines are so easy to start (they restart in a fraction of a second), there's really very little additional demand on the starter and battery.

The only real downside we've found is that the restart (on some cars) can be a bit annoying. Some manufacturers haven't executed these systems as smoothly as others. Buick and GM actually do it pretty well, but on some cars, you can feel a little shudder every time the car restarts.

The heating and cooling fan keeps running (along with important accessories like the seat heaters and the radio) when the engine shuts off. And if the temperature in the cabin gets out of its acceptable range (which it rarely does during a 60 second traffic light), the engine will turn itself back on and fire up the compressor.

As you've discovered, restarting is instantaneous, as soon as you take your foot off the brake, so there's no making anybody wait behind you. In fact, a BMW we drove recently uses its automatic emergency braking sensor to tell when the car in front of you starts moving, and it restarts the car when it sees that, even before you take your foot off the brake. Pretty smart!

So, we're with you, Tom. We don't love these systems, but we got used to them. The environmental benefits alone make the case for everybody using them.