Tips: Save on Fuel on Full Tank

Just yesterday fuel pump prices increased by more than 1 peso. It was good thing a day earlier I had our two cars filled their tanks to full. Our SUV's full tank is 75 liters of diesel while a small car was at 43 liters of gasoline. Then it hit me if carrying around the extra weight of the fuel affects my mileage at all. So to satisfy my curiosity and peace of mind, I researched and evaluated if is it worth to get a full tank (to avoid the price increase) versus carrying around extra fuel weight (affecting my fuel consumption).

Here are some information (mostly from the internet)  I have searched to be used for my evaluation:

1. 1 liter of diesel has a weight of 0.851kg or 1.872lb (source: google search)
2. 1 liter of gasoline has a weight of 0.749kg or 1.648lb (source: google search)
3. The study Impact of Vehicle Weight Reduction on Fuel Economy for Various Vehicle Architectures by Ricardo Inc. for The Aluminum Association in 2008 showed that

      a. for a small car a 100-lb weight reduction resulted to 1.7% improvement in fuel economy city driving
      b. for a large SUV a 100-lb weight reduction resulted to 0.9% improvement in fuel economy city driving



 So how does it compute? For example for our SUV, the full tank is 75 liters of diesel which is about
140 lbs. Let's say if I want to remove 100lbs of excess weight driving around MetroManila, I will only fill to 30 liters. With this, my mileage would improve by 0.9%. Let's assume that I would have save 0.9% of my 75 liter full tank which is about 0.75 liters. I would have about 32 pesos per full tank. Compare this versus a price increase of 1 peso and full tank of 75 liters equivalent to 75 pesos saved.

For a small car, filling up to half full will reduce my weight by more than 35 lbs. The equivalent fuel economy improvement is about 0.62%. Now that's equivalent to 12 pesos. Compare this versus a price increase of 1 peso and a full tank of 42 liters equivalent to 42 pesos saved.

Hmm so what's the verdict? I will not definitely drive around MetroManila on a full tank. It will improve my fuel economy saving me at least 1 liter of fuel, helping in the carbon monoxide reduction. I will only fill our cars to full if there are scheduled fuel price increase of more than 50 centavos.