There’s only one way to cheap out on car AC

Dear Car Talk: I am cheap. Starting out on a hot day, I turn the air conditioner on. I set the AC to “max,” I turn the temperature all the way down, and I set the fan on “high.”

When it gets too cool, I first turn off “max.” And then when it gets too cool again, what should I do? Remember, I AM CHEAP!

Should I turn down the fan? Is the AC still running full blast and I’m just not getting all that I’m paying for? Or should I turn up the temperature and set it a little warmer?

Is the AC cutting in and out as needed, like the AC in my house? Or are they just mixing in a little hot air if I turn up the temperature?

What should I do? I love your old show, which I still listen to every week. Thanks. – Ken

RAY: You should go out and buy yourself a pair of Egyptian cotton Bermuda shorts, Ken. And drive around with the AC off.

Actually, the answer to your question is it doesn’t really matter. In terms of what it’s costing you (which is the essence of your question), none of the actions you list here are going to save you any money.

The AC in your car does cycle on and off, like the AC in your house. That happens regardless of how you set the temperature. The fan speed has no bearing on how hard the AC works. It just blows softer or harder and changes how much cold air you feel blowing on you.

Turning off the “max” setting doesn’t save you anything either. When you set the AC to “max” (also called “recirculate” on some cars), it simply recirculates more of the air in the cabin that it has already cooled, and draws in less warm air from outside the car. That helps to cool the cabin faster, but doesn’t change the power demand.

If you turn up the temperature setting, that won’t save you any money either. It’ll just blend in some warm air to raise the temperature while the AC pumps away. In fact, that’s what automatic climate control systems in cars do. To maintain your chosen temperature, they’ll run the AC and blend in more or less warm air to keep the temperature constant.

I’m sure you don’t have an automatic climate control system in your car, Ken, because you’re what? Cheap! So the only way you’ll save any money is by turning off the AC entirely. That will reduce the demand on the engine, which will increase your mileage a bit, which will ultimately save you a few bucks at the pump.

Oh, but I almost forgot to mention: You can’t open the windows. If you open the windows at moderate to high speeds, you’ll mess up the airflow around your car and make it less aerodynamic. That’ll more than wipe out any increase in mileage you get by turning off the air conditioning.

So you can only open the windows in stop-and-go traffic, when there’s no breeze. How’s that sound, Ken? But that’s how you can save money. Turn off the AC and keep the windows rolled up.

Just be aware that your wife’s going to divorce you due to the way you smell every time you get home, so don’t forget to subtract alimony from all of your savings. Good luck, brother.

Do all of the tires need to be replaced on this Ford Fusion?

Dear Car Talk: Do I really have to replace all four tires on an all-wheel-drive 2007 Ford Fusion when one tire is destroyed? – Nathaniel

RAY: You might.

The problem is that all-wheel-drive cars have something called a center differential. A center differential is a box of gears that allows power to be transmitted to all four wheels, while at the same time allowing the wheels to turn at different speeds when they need to.

When do they need to? When you turn. Whenever you turn left or right, your inside wheels always turn slower (and travel less distance) than your outside wheels. If you don’t believe me, steal one of your kids’ Hot Wheels cars and turn it in a tight circle on the kitchen table.

Here’s the problem: If you have one new tire that’s larger than the other three, that new tire will always be turning more slowly, forcing the center differential to work. And the center differential is not designed to be in use all the time – like when you’re driving at 75 mph down the interstate.

If you think tires are expensive, Nathaniel, go out and price a differential. That said, there are a couple of situations in which you might not need four new tires.

If you bought the other three tires recently, you might get away with buying one new one. Every manufacturer has a limit to how much difference they allow in tread. So if the difference in the tires is 3-4/32nds of an inch, check with your manufacturer and see if that’s allowable.

If not, and if your tires still have a lot of life on them, you can consider buying a shaved tire. No, that’s not a new manscaping term you haven’t heard of yet, Nathaniel. A shaved tire is a new tire that has its tread shaved down with a special machine to match the amount of wear on your other tires.

You might be able to find a tire shop locally that does it. If not, go to tirerack.com. They’ll sell you the matching tire, shave it for you for $30 of so, and deliver it to you or to a local installer.

Even though it seems a bit wasteful, that might be the most cost-effective solution of all, short of stealing all four tires from your neighbor’s Fusion.