Tuesday, July 23, 2024 Detailed Auto Topics
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Filling my vehicles with fuel, is something I really dislike.  Not only is it expensive, I also find it inconvenient.  This creates a temptation to make either of two major mistakes.  I like to get the most miles per tankful that I can.  This requires care, because there is damage when we run a fuel tank too low or when we overfill it.

Running the tank too low            

Running the fuel level low may damage the fuel pump

Fuel pumps are electrically powered but mechanical in nature.  An electric motor turns a pump, which creates a precise fuel pressure.  All mechanical devices, that move, need lubrication.  The fuel flowing through the pump provides this function.  Fuel flow also acts as a coolant, and removes heat, generated by the motor.  

Modern fuel pumps are found near the bottom of the tank.  Fuel has weight and provides static pressure to the inlet of the pump.  Using fuel will lower the weight and static-boost available for the pump.  A lower fuel level means the pump works harder.  Temperature of the pump rises as it strains to keep up.

Unfortunately, as the level drops, there is less liquid to act as a coolant.  The pump is working harder and there is less to cool it.  Wear accelerates and inevitably; failure will occur.  Older vehicles operate with less fuel pressure and often have fuel regulators at the engine.  Lower pressure means less work and the loop from the pump to the regulator provides additional cooling.

Today, fuel pumps produce higher and more precise pressure.  Normally, they regulate this design from within the tank.  This eliminates the loop that helps provide cooling.  Heat and lack of lubrication are a larger problem with such systems.  Running modern fuel-pumps without fuel may damage them, with just one occurrence.  To be safe, consider the quarter-tank mark as time to refill.  

Overfilling the fuel tank

If a person dislikes filling their tank, it is tempting to fill it as full as possible when they do.   Continuing to add fuel, once the dispenser nozzle clicks off the first time, is not a good idea.  Air must enter the tank as the fuel runs out.  To allow this, they vent the tank.  A storage device captures the fumes that would escape into the environment.  'Topping off' the tank can cause fuel to back up into the charcoal canister, designed to store only fumes.  

Continuing to fill the tank will damage the evaporative emissions system

Evaporative emissions systems are complex and designed to work only with vapors.  Liquid fuel damages the charcoal canister.  When the canister breaks down, debris enters the system.  Liquid fuel will damage the valves, solenoids and sensors, and the check engine light comes on.  This is expensive to repair and often preventable.  When the fuel nozzle cuts off the first time, quit adding fuel.

What to do instead

Fuel-range is how far a vehicle will go before the tank runs low.  Three main factors influence the distance.   First is the size of the tank.  When selecting a vehicle, ask how large the tank is.  Fifteen to twenty gallons means less often filling of the tank.  Second, is the fuel mileage the vehicle delivers.  This varies with design and is nearly impossible to increase significantly, other than with the following methods.

Driving faster burns more fuelDriving style is by far the largest factor in determining fuel consumption.  Fuel is energy. To drive faster, we will need more.  Running a mile requires more energy than walking the same distance.  Vehicles also adapt to drivers’ habits.  Accelerate rapidly and shift-points extend producing more power.   A change of driving style may allow 100 additional miles, with a tank of fuel.

Driving slower and accelerating more gently extends the time between gas-station visits.  It also does no damage and extends the life of a vehicle.


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