Since it's Friday the 13th, it's a good time to talk about my top ten automotive superstitions.
1. Fuel economy is best with a full tank of gas.
Everyone knows that a fuel gauge takes longer to move from full to the half-way point. After half-way, the gauge needle moves faster and faster on its way to the big "E." This must mean there is a difference in fuel economy? Wrong, Grasshopper. This phenomenon is caused by the design of the sending unit in the fuel tank. Due to the way these units must produce an electric signal, they must function in a NON-LINEAR manner. In English, the signal is less sensitive at the top of the gauge than the bottom.
If you want to mess with someone's mind, the next time they ask how much fuel you have, tell them you have half a gauge of fuel...or a quarter, three quarters, (whatever the gauge is reading) Not only will you catch them off guard, you'll be more accurate in your statement.
2. A clean car runs better.
Not sure who made this one up but it sure is popular and as sure as there is no possible connection between cleanliness and a car/truck that runs purrfectly, I'm still here to tell you that at the emotional level, it sure feels as though there is truth to this myth.
3. It's good luck to have bird poop on car.
With Basecoat/Clearcoat paints now the norm, this couldn't possibly further from the truth. The acid in bird poop ruins a modern finish.
4. Hi-test fuel works better than low grade.
I wish there was a way to spell the sound that that annoying buzzer makes on TV game shows. ENNGGHH! maybe? Anyway, with the computerized engine controls found on vehicles built since 1986, this statement is no longer true. That said, there was a time, when contact points and carburetors were found under the hood, that this was valid.
5. Always keep your gas tank full.
This is actually true. It's as much a safety item in the winter as anything, and in the summer a full tank prevents condensation build-up.
6. Always warm up your engine before you head out.
The jury is still out on this one. There are many factors that dictate how you approach warm-up periods. All things equal, you are better off to simply start your engine - and go.
7. Buy your gas in the morning when it's colder and denser.
ENNGGHH! Nope, fuel station dispensers have electronic calibrations that compensate for volume changes due to temperature. If you look hard, you may even see a little sticker that states this.
8. Fuel economy is better with air conditioning on rather than the windows rolled down.
Annoying sound again! There is no perceptual difference between these two conditions. As a matter of fact, by NOT using your A/C, you lose the "conditioning" part of air-conditioning. This is a topic I will cover on another day.
9. Lowering a car's suspension automatically improves the handling.
Auto manufacturers spend gazillions of dollars on R&D to produce a balance of handling, safety and comfort on a car or truck's suspension. For us to think we can re-engineer a vehicle in an afternoon in our buddy's garage by cutting or heating spring coils, installing drop axles, etc., etc., well, you get the picture. However, there are instances where the opposite is true. I'm talking about the manufacturer-supported equipment that can be installed to enhance a vehicle's handling characteristics.
10.Inflate tires based on the numbers on the sidewall.
If you take the time to read the wording that surrounds the inflation numbers on a tire's sidewall, you'll notice that these numbers relate to the maximum carrying capacity of that tire when inflated to that pressure. This is interesting because the weight that's noted is for a single tire. Using this thinking, the total weight, (all four tires' weight capacity added together) you will find that this number will usually exceed the vehicle's capacity. The inflation number on the sidewall is used as a benchmark because the same tire could be fitted to a variety of vehicles with different weight carrying capacities.
There you have it, my picks for the top ten superstitions or myths that I often get asked about. This list is certainly not the be-all-and-end-all and I'm sure many of you have your own favourites. It would be interesting to hear what you have to add or subtract to this list for the next Friday the 13th.
E-mail Rob with your car maintenance questions at email@example.com