Dear Car Talk:
The owner’s manual of my car — an Audi A6 — says to use 91-octane fuel. But the pump near me has 87, 89 or 94. Since then, I’ve noticed that a lot of cars require 91-octane.
Is this a case of where they sell hot dogs in packs of 10 and hot dog buns in packs of 8? Am I just out of luck? Or can I mix some 89-octane with some 94-octane and drive happy? — Bill
Drive happy, Bill. You can absolutely mix octanes, and they mix linearly. So, if you could fill half your tank with 89 and the other half with 93, you’ll end up with a tank of exactly 91-octane.
If you go with half 89 and half 94, which is what’s available near you, you’ll end up with 91.5-octane. Which is close enough, Bill.
And the truth is, you don’t have to stress about it. The engine has a computer management system that will adjust for lower-than-recommended octane fuel. So, if the computer senses pre-ignition (aka pinging or knocking, which can result from too low an octane), it will adjust the timing to correct for that.
You’ll have a little less power — probably not enough of a difference to notice — but your engine will be protected against any damage from fuel that ignites too early.
So rough math is good enough here, Bill. You don’t need to go to the Sunoco station with measuring spoons.
Dear Car Talk:
In a recent column, Phyllis, with a 2015 Camry, wrote that she hears a pop when she drives it. I have the same problem with my 2015 Camry and thought it was something in the suspension.
I took it to the dealer and they said it was a known problem. Evidently it is with the rails for the sliding moon-roof. To fix it, they would have to remove the liner and replace the rails to a tune of $2,300. I will live with it. A bummer since the problem started three months after my warranty expired. — Tom
This is a good argument for going to the dealer if you have an unusual or hard to diagnose problem.
Sometimes, the place that works on 2015 Camrys every day will know exactly what it is and save you the time and money you’d spend having someone else figure it out.
It’s true, you might end up with an estimate that makes you say, “ah, never mind, I’ll live with the pop.” But at least you now know that it’s not dangerous, Tom. So now you can wait until the sunroof starts leaking or until an anvil falls from a 10th-story window onto the car, and then have the rails fixed at the same time. Thanks for the info, Tom.
Got a question about cars? Write to Car Talk write to Ray in care of King Features, 628 Virginia Drive, Orlando, FL 32803, or email by visiting the Car Talk website at www.cartalk.com.
