Green Driving Series: Four Reasons You Shouldn’t Top Off Your Gas Tank

The first article in the Green Driving Series highlighted some of the best and worst vehicles on the road from a green standpoint.  The second article focuses on my favorite green driving tip:
Don’t top off your gas tank.

Here are four reasons why you shouldn’t top off your gas tank:

1. The gasoline could spill

The possibility of gasoline spilling out of your tank while topping off comes with a handful of reasons why you shouldn’t top off.  Gasoline is a hazardous substance.  The fumes are toxic and carcinogenic.  Spilled gasoline seeps into groundwater, polluting our water and poisoning wildlife.  Gasoline is flammable.  It’s a waste of money – after all, you’re paying for the gasoline that spilled.

2.  It’s a waste of money

The vapor recovery systems on most gas station pumps will draw in the extra gas you’re trying to pump into your tank and feed it back into the station’s storage tank.  So you’re actually paying more for gas you aren’t getting.

3.  Topping off could cause the gas pump to fail for the next person

The fuel that is fed back into the station’s vapor recovery system when you overfill can also cause the pump to malfunction, creating a domino effect of possible overfilling and spillage for the next person.

4.  May cause damage to your vehicle

Extra room in the gas tank is needed for the gasoline to expand.  Topping off can cause the extra gas to overflow into your vehicle’s vapor collection system.  Best case scenario is that you’ve wasted more gas, worst case scenario is that you have fouled up your car’s vapor system – a costly mistake.  The fuel in the vapor collection systems will also cause your car to run much less efficiently, another waste of fuel and money.

As one example, we looked at Toyota’s Hybrid System Diagnosis Technical Training Manual for the Fuel and Evap System and found the following information about overfilling:

Trying to force additional fuel into the tank pushes excess fuel into the EVAP system.  This may cause an EVAP DTC and may even require the replacement of some EVAP system components.

DTC P1455 can occur from overfilling the vehicle which can cause raw fuel to collect in the lines. In extreme cases the fuel may run back down the vapor pressure port and contaminate the outer tank. The most common cause for this code is “topping off” the fuel tank or not fully inserting the nozzle into the filler neck during refueling.

In either case, excess pressure during refueling can force fuel through the vents at the top of the filler neck or the Fuel Cut?Off Valve, and can get into the Charcoal Canister or outer area of the Bladder Tank. If you get this code remove the Vapor Pressure Sensor and sample the tank with an emissions or 134a sniffer.

If HCs are detected, replace the fuel tank, canister and lines. It is important to educate the customer about proper refueling to eliminate this problem.

So the next time you fill up at the pump you may want to fight that urge to round off your purchase to the nearest dollar or squeeze in a few more drops with the hope that you can drive 5 more minutes before your next fill-up.  You’ll save yourself some money and avoid contributing even more to air and water pollution.


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