Chasing down an intermittent nonstarter

Dear Car Talk:

I have a well-maintained, 2008 Ford Fusion with 256,000 miles. Sometimes, the car does not start on first, second, third or more turn of the ignition key. I’ll pump the brake and keep at it, and finally it starts. There’s no signs of life during these failed attempts (no sound at all).

I had the battery replaced a couple of months ago, but it's still happening. Is it the starter? Loose connections? I'm getting ready for a long road trip and don't want to be stranded. I'd like to give the dealership some hints about what to look for in case the car starts fine when I take it in. What should they check? – Christie

RAY: Well, with 256,000 miles on the car, it could be a lot things. It's like when a 96-year-old comes into the doctor's office, and the doctor asks "Is anything OK?"

I’m going to guess it’s not the battery, since that was just replaced. And I’m also going to guess that when they changed out the battery a few months ago, they cleaned and tightened all the cables. So it’s probably not that, either.

It could be the starter motor. This is classic behavior of a failing starter. It could also be the ignition switch. The ignition switch is what you stick your key into. And after a few million uses, it can wear out, and fail intermittently.

In addition, there are a couple of safety features that prevent you from starting the car and immediately plowing through your garage door. One is called the neutral safety switch. That’s a switch that prevents the car from starting if the shifter is in anything other than Park or Neutral.

As an experiment, next time the car won’t start, with the transmission in Park, try forcefully jiggling the shifter with one hand while holding the key in the crank position with the other. If nothing else, it’s good aerobic exercise.

If you can get the car to start that way in Park or Neutral, that points to a bad Neutral Safety Switch.

Your Fusion also has a brake-starter interlock, which prevents the car from starting unless your foot is on the brake. If that switch is out of position, or worn out, that could also cause intermittent starting issues.

So this is good news for your mechanic, Christie. He’ll have plenty to choose from, in terms of where to get the money for next month’s boat payment.

And you’re right to get it addressed before your upcoming road trip. These “intermittent” problems tend to become more “mittent” over time, and then permanent. So it certainly could strand you.

If you’re not able to confirm it’s the neutral safety switch by using the experiment I describe, ask your mechanic to take his best guess and try replacing something.

You’ll have to hope that he guesses right, or that if he guesses wrong, it fails again before your bon voyage party.

If it were me, I’d probably start with the brake interlock switch first, since that’s the cheapest thing to try. If that doesn’t fix it, I’d try a new starter motor. I’d try the ignition switch last.

And each time you’re in there for one of these repairs, don’t stop yourself from perusing the new car showroom. Good luck, Christie.

Husband under pressure to keep tire warning light satisfied

Dear Car Talk:

My question has to do with the air pressure in my tires. In the winter, the low tire pressure warning light in my wife’s car tends to come on when it gets very cold. As I’m sure you’re well aware, this is due to the impact of the cold on the density of the air in the tire.

I live in Colorado, and it can be 14 degrees in the morning, and in the 60s by the afternoon. When I check the pressure early, it’s naturally low. When I check it in the afternoon, it’s back up to normal.

My question is this: What pressure should I set the tires at so that I can assure my wife that she is safe to drive, and will also prevent her sensor from sending her into a panic, and me having to check her air pressure to convince her that she does not have a flat tire? Thanks. My frozen fingers thank you as well. – Dave

RAY: Good question, Dave.

Keep in mind that, generally speaking, tire pressure that’s too low is more dangerous than tire pressure that’s too high. So the answer is to fill the tires so that that they’re at the correct pressure at the colder part of the day.

We know that tire pressure drops about one pound-per-square-inch (PSI) for every 10 degrees the temperature drops. So, if your recommended tire pressure is 30 PSI, and you set them at 30 PSI in the afternoon when it’s 65 degrees, by the next morning, when it’s 50 degrees colder, your tire pressure will be 25 PSI.

That’s more than 10% below the recommended pressure, so it’ll set off your tire pressure warning light, panicking your wife, and setting you on a path to frostbite.

So, instead, set the tires at 30 PSI in the morning. By the afternoon, the tire pressure will be 35 PSI, and that will be of absolutely no consequence in terms of safety.

If your wife is very sensitive, she may notice that the ride is slightly firmer. And if she’s an engineer, she may notice that she gets better gas mileage in the afternoon with her firmer tires than she does in the morning. Realistically, she probably won’t notice either (and neither would any of us).

As long as you stay below the tire’s maximum safe pressure (which is printed on the sidewall of every tire, and is considerably higher than the recommended pressure), your wife will be perfectly safe. At 35 PSI on a passenger car tire, you shouldn’t be anywhere near the tire’s maximum allowable pressure.

So in circumstances like yours, where the temperature varies wildly, set the correct pressure during the colder part of the cycle, Dave. Then you can both live like normal adults and stop thinking about your tires.

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