Sunday, April 23, 2006

Do Not Top Off

Some time after May of 1995 my wife stopped filling the gas tank of whatever vehicle she happened to be driving. I wasn't crazy about this at first, but then it just became something that I did as a weekly routine. It gave me a chance to monitor the mileage of the vehicles--which was something I actually used to keep track of--and do little things like clean the windshield, check the fluids and all that good stuff.

I am such a creature of routine. There were a couple of things I always did (and continue to do) when putting gas in the car. First, I always wait until there is less than a quarter tank to refill it. Most people do, I think. It's just a matter of lengthening the amount of time between fill-ups. Second, I always fill the tank. I never just put five bucks in , or five gallons. I always fill it. Why? Well, I guess it's the same reason I always reset the odometer--to get an accurate assessment of my fuel consumption per mile. Even now I reset the odometer--every time--even though I never calculate the mileage. Weird.

Somewhere along the way I reasoned that I could never get a true and accurate measurement of the efficiency of the fuel I was consuming unless I knew exactly how much I was putting in. Could the automatic shut-off on the gas pumps be trusted? I didn't believe so. Especially if I went to a number of different gas stations, their mechanisms could all be very different. What if some filled me up to the top and others left a half gallon in the tank? The only way I could be sure of the most accurate measurement is if I could see exactly what was in the tank--i.e., if I could just top it off--even very slowly, I could see just where the fuel level was at the place the nozzle goes in.

Then I started noticing these little signs appearing in various places around the gas pumps. "Warning: Do Not Top Off." "Yeah, yeah, yeah," I thought, "why not? They just don't want me to spill it. I don't spill it. I'm very careful."

Finally, this week I decided to try to do a little research as to why those signs appeared at every gas station. Was it the law? Was it a suggestion? Was it personal preference?

I've since found some compelling reasons to stop topping off the tank.

  1. If you over-fill your tank, the vapor recovery system, installed on most gas pump nozzles will actually suck some of the extra fuel that you just thought you used to top off your car back through the vapor line and back into the storage tank. The bad news is, of course, this fuel has been metered and you've already paid for it!
  2. Topping off your tank affects your car's vapor collection system which in turn will cause your car to run inefficiently.
  3. Spillage. This is always an issue and no matter how careful you may intend to be, you still may spill some gas outside your car. It messes up your paint and can create a potentially hazardous mess for the next customer.
  4. Gasoline expands after it is retrieved from the cool tank in the ground. If you fill your tank to the top, you leave no room for the gas to expand, further sabotaging your car's vapor collection system.
A couple of other items of interest. 1. Fill up your gas tank in the morning or the evening when the gasoline is most dense. You will find that you can get more gas for your dollar (or dollars) at these times. 2. Make sure your gas cap is on tight and doesn't leak. Some metro areas require a gas cap check. This is for environmental reasons as well as efficiency reasons. It is estimated that 147 million gallons of gasoline evaporate through faulty gas caps each year. 3. Make sure your air filter is clean. A dirty air filter will make your car run rich, which obviously consumes more fuel but also wears more on your spark plugs.

It's a habit I'm going to have to learn to break, and even though I know I'm gonna feel like I'm not getting enough gas, from now on, I'm going to resist the urge to top off the tank! What do you usually do?