Arthur: About a third of a gallon, Arthur.
Most gas pumps work by blending octanes right at the pump. Instead of having three to five underground tanks of fuel, a gas station would, for instance, have one big tank of 87 and one big tank of 93 and would blend them at the pump, on demand, to make everything in between.
Gasoline gets pumped out of the underground tanks and pushed, under pressure, to the gas pump, where it’s blended into whatever octane you select. That blend is then pushed through the fuel hose and the filler nozzle and into your car.
When you release the handle on the nozzle, or when the nozzle clicks off automatically when your tank is full, the fuel is shut off at the nozzle. The hose remains full of fuel.
So, if the person before you used 87 octane, the first third of a gallon you’d get would be 87 octane, Arthur.
In a tank-full of 12 or 14 gallons, that makes no difference to the car. For example, if you have a 12-gallon tank, and the first third of a gallon is 87 and the rest is 93, your overall octane would still be something like 92.83.
And if the person after you chose 87, they’d get a third of a gallon of 93 and end up with an overall octane a smidge higher than 87, which wouldn’t matter to their car either.
The department of weights and measures approved this method several decades ago, after concluding that it had no meaningful impact on cars or drivers. Although I understand how it can frost your shorts, Arthur.
The people who have to be careful, though, are motorcyclists. When you have a 3-gallon fuel tank, a third of a gallon can make a meaningful difference in overall octane. And not all motorcycles have the ability to adjust for varying octanes the way modern cars do.
So motorcyclists may have to hover around the pumps, like waiting for a table to free up at Starbucks, and pounce as soon as an Audi pulls away.
Dear Car Talk: I recently discovered that the lens is missing on the center brake light on my wife’s 2016 Lincoln MKX.
The dealership (where we bought the vehicle) quoted more than $650 to replace the whole unit. Apparently, you can’t replace just the red, plastic lens. The service tech confided in me that they had replaced the center brake light on three such vehicles recently, and that they were all lost in car washes.
I am a do-it-yourself kind of guy and found a third brake light unit online for $160. Do you think this is the type of project an average Joe can handle, or should I cough up the money to the experts?
It just grates me that something as simple as a brake light lens is so complicated and expensive to replace. Thanks in advance for any guidance and assistance you can offer. — Jerry
Jerry: Can an average Joe handle this? Well, an average Joe with lots of patience and no young kids nearby to hear him cursing.
I’ll be honest with you, Jerry. It’s a pain-in-the-butt job. It’s not a good design, in terms of repairability. You have to remove the car’s upper rear spoiler. Lincoln decided to attach the rear spoiler with a bunch of plastic push-pin locking fasteners that are almost impossible to get at and remove. It can be done, but it’s slow and frustrating.
So maybe you could just go through a more powerful car wash and see if it’ll rip the whole spoiler off? It could take you hours to remove. I’d suggest going on YouTube and watching a video or two of it being done. You may pick up some time-saving tips. Or you may run to your dealer and fling $650 at him. Once you get that spoiler off, it’s actually an easy do-it-yourself job. And getting the spoiler back on is a lot easier than taking it off.
One other option is to stop by a body shop and ask them what they’d charge to do the job for you. They do this kind of work all the time when doing post-collision repairs. Maybe they’ll be cheaper.
Whoever does it, have them make sure the edges of the lens are flush with its housing. If the lens is mis-manufactured, or sloppily manufactured, it can leave a lip, which should be sanded or ground down. Otherwise, the new one will be vulnerable to being torn off in the car wash, too.
Got a question about cars? 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.
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