Dear Car Talk:

We have just purchased a new 2017 Jeep Cherokee. We love it. But it has one irritating “feature” that is quite annoying: The engine cuts off at every stop — presumably to save fuel — and then restarts when I take my foot off the brake. How can this be good for the longevity of the starting components: battery, starter, solenoid, flywheel, etc.? When the engine stops, the air conditioner and radio keep running, further draining the battery. There is a button on the dash to cancel out this feature, but it must be re-engaged after every start. Is there a way to program this to default to the alwaysoff position rather than the always-on? Thanks. — Bill

Not that I know of, Bill. Automatic stop-start is on lots of new cars now. It increases your mileage by a few percent because your engine isn’t idling when you’re sitting at a traffic light. It also eliminates pollution from cars sitting idle at traffic lights, which is great for cities.

But it’s still a relatively new feature, and some manufacturers seem to do it better than others. We test-drive cars all the time, and on some, the stop and the restart are barely perceptible — if you were paying attention, you’d notice it, but it wouldn’t bother you. Then there are other cars that restart with a mild earthquake of a shudder, and that quickly gets annoying enough that we’ll turn off the feature.

I’m not sure what factors make some cars entirely acceptable and others not. But I suspect they include the quality of the engine mounts, the amount of insulation between the passenger compartment and the engine bay, and the mass of the engine itself, with smaller engines being easier to make subtle.

That leads us to the next thing that’s different from car to car. I’d say most cars require you to turn off the automatic stop-start each time you drive the car. A few will remember your preference the next time you drive, but that’s a minority.

I’m guessing that the car’s mileage rating would be dinged if an owner could easily, and permanently, turn off the start-stop. So the manufacturer wants to discourage that. And besides, the benefits are meaningful. Not just for you, but for everyone breathing nearby.

My heater core started leaking, so I plugged the hoses going to the heater. I live in Hawaii, so I don’t need the heater. After a few months, I noticed that the plugs I had installed had started to crack. They’re not the same-quality rubber as the hoses. So, I replaced the plugs with a hose that just connects the coolant line going to the heater core with the coolant line coming from the heater core. Then I started to notice that the car runs rough in traffic. Did I do this wrong? — Charles

“Don’t need heat.” Sure, rub it in, Charles!

You did it exactly right. You basically take the two hoses off the heater core, you stick them together and you’re done. That way, the coolant will continue to circulate, even though it no longer goes through the heater core.

And bypassing the heater core should have no effect at all on the performance of the engine, Charles. So there’s something else wrong that’s causing your rough engine operation in traffic.

What else did you “fix” recently, Charles? I’d start there.

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