Dear Car Talk: Help! My wife and adult daughter have started a practice that worries me. In the hottest part of the summer, they like to turn on the air conditioner in the car AND roll down the window!?!
They say they like the coolness, but they also enjoy the fresh air. I say your car’s air conditioner is being used excessively and is killing your gas mileage.
Should I be worried or just consider them crazy? – Michael
Dear MIKE: I do this too. When it’s really hot outside, there’s nothing I like better than having the A/C vents blowing just below the belt and blowing cool air in my face. Especially when driving around town. I just don’t like being locked in a hermetically sealed car.
Is it a waste? Yes. Having the windows down, at least at higher speeds, worsens the car’s aerodynamics, thus reducing mileage. The air conditioner itself doesn’t necessarily work anymore, it’s either working or it’s not working. But your overall fuel consumption will increase.
How do I defend it? not very well I’ll confess that, like many of us, I’m sometimes willing to give up a little efficiency for a little comfort. I guess I’ll have to answer to St. Peter for that. And my electric company.
But before you claim the moral high ground and go after your wife and daughter, Mike, make sure you’re not vulnerable to counterattack, Mike.
For example, you are right that it is more efficient, on the highway, to drive with the windows up and the air conditioning on.
But you know what’s even more efficient? Drive with the windows up and the air conditioning off. Girls may insist that you model this exemplary environmental behavior if you insist on being the moral arbiter of their energy use.
And speaking of the environment, if you go this route, Mike, make sure you drive with a glove box full of deodorant and extra t-shirts. And he plans to drive alone a lot.
So the bottom line is, you’re right, Mike. At freeway speeds, they reduce their mileage with the windows open by reducing the aerodynamic efficiency of the car.
Maybe you can get them to compromise and keep the windows down on the freeway and let them roll down the windows around town where the aerodynamics don’t make a difference.
Or, just accept the reality of the situation: there are two of them and one of you. Good luck bro.
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Dear Car Talk: I have a 2020 Honda CR-V with 18,000 miles. The maintenance supervisor says I need to replace the rear diff fluid and brake fluid now. This seems excessive to me.
What interval do you recommend as the appropriate time to change these fluids? -Dave
DEAR DAVE: It’s not as simple a question as you might think. Recommendations like these are based on science. But it’s not an exact science.
Two factors are involved: mileage and time. Mileage, which is a rough measure of how much use the fluid gets, matters a little more to me. The more a fluid is used, the hotter it runs, the dirtier or more contaminated it is, and the closer it gets to the end of its useful life.
The other factor is time. Time does matter, because some chemicals or chemicals degrade over time. Or, in the case of brake fluid, if it already contains all the moisture it can hold in suspension, you don’t want the excess moisture to dry on the brake lines and corrode them from the inside.
Honda gets on the side of time here. Your maintenance monitor turns on after three years of driving. Honda probably assumes you’ll be around 36,000 miles by then, like the average driver. But they obviously believe that weather is also a factor, and they may have data to back it up in their cars. I do not know.
So my answer: I don’t think there’s much of a rush to change any of these fluids. I doubt anything terrible will happen if you wait another year or even two, given your low mileage.
On the other hand, I would be inclined to change the brake fluid sooner rather than later. Surely it’s a bit early? Yes. But it’s not an expensive job (probably $150 at an independent mechanic, possibly a bit more at the dealership), and if you plan to keep the car for a long time, it’s the safest thing you can do for your brake system.
I would be willing to wait longer on the diff fluid. These cars have a problem where when the diff fluid degrades the diff will “clunk” in sharp turns.
Honda’s solution is to have the differential fluid changed before it has a chance to degrade. But I don’t recall seeing a CR-V in my shop with a chattering diff with such low mileage. We tend to see this at over 75,000 miles. So I would like to wait a year or two to do that.
And of course, if you ever notice wheel chatter in sharp turns, then I would take it and change it, and that will fix it.
But none of these are emergencies, Dave. You don’t have to cancel your dentist appointment tomorrow to rush to the store to buy brake and differential fluid.
Ray Magliozzi dispenses car advice on Car Talk every Saturday. Email him by visiting him cartalk.com
