Diesel Fuel Temperature

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A long, long time ago, when I barely had any driving experience at all, my dad told me to buy gas for my van early in the morning instead of late in the afternoon. All well and good but I was a teenager; the only early morning hours I saw occured before I went to bed; not when I woke up. The breaking dawn was something I'd heard of but had never really seen for myself. Consequently, I usually bought gas while the sun was riding high in the sky.

So; you might be wondering why my dad gave me this sage, yet unfollowed, advice. The answer: gasoline and, for that matter, diesel fuel expand and contract with the temperature. This isn't news; you probably learned about the effects of temperature on liquids, solids and gasses sometime before you entered high school. I know I did. My dad just wanted me to get the most fuel for my money by purchasing the coldest available gasoline. He knew that hot fuel was less dense and, therefore, contained less energy than more dense cold fuel. In other words: hot fuel results in fewer miles to the gallon.

Diesel Fuel Delivery - Regulations

The diesel fuel delivery regulations, which have been in place for nearly a century, stipulate that diesel fuel be delivered to the pump at 60 degrees farenheit. At 60 degrees the volume of one gallon of diesel fuel is 231 cubic inches and diesel fuel pumps are metered to deliver a gallon of fuel equal to the 231 cubic inch standard.

Even though truck stops measure out your fuel delivery as if it were stored at 60 degrees, however, no law requires them to adjust the pump to reflect the expansion of hot fuel. In other words, no regulation ensures you get what you pay for.

Diesel Fuel Physics

As we know, diesel fuel expands and contracts depending on temperature. At the 60 degree, 231-cubic-inch, standard a gallon of diesel fuel contains a specific amount of energy. At 90 degrees, however, the same amount of diesel fuel expands to more than 235 cubic inches; but truckers still receive the standard 231 cubic inches at the pump.

You've no doubt surmised that every degree, over and above the 60 degree standard, diminishes the energy contained in a 231-cubic-inch gallon. This results in lower MPG and higher consumer costs. But, what about cold fuel? Read on.

What Can Be Done?

The technology exists to retrofit diesel fuel pumps with metering devices that adjust the flow to reflect changes in fuel temperatures. Still; oil companies, retailers, and the American Petroleum Institute (API) have successfully argued, for decades, that retrofitting pumps would cost too much and that consumers just wouldn't understand fuel pumps that adjust for temperature change.


This is where the discussion of cold fuel becomes interesting. Even though oil companies and retailers have generally dismissed the idea of temperature adjustment in the U.S., where hot fuel increases their bottom line, temperature adjustment has been welcomed with open arms in Canada. Why; you may ask? Well, high density, energy packed, cold fuel was decreasing the bottom line for oil companies and retailers.

In 1990 a Canadian law, supported by oil companies and retailers, went into effect. The regulation permitted retailers to adjust for temperatures on a voluntary basis and supporters of the law said the change brought "fairness" to the marketplace. It's now estimated that 95% of Canadian retailers adjust for temperature at the pump. Interesting; when temperature adjustment benefits the oil companies and retailers it's "fair" and, when it doesn't, it's "costly and unnecessary".

The Cost of Hot Diesel Fuel

While costs may seem small, there are a few things that have happened in the last ten or twenty years that have brought the issue of hot diesel fuel to the front burner:

The National Institute of Standards and Technology has determined that the year round average temperature of diesel fuel sold in the U.S. is 65 degrees. Considering current consumption patterns; the increased temperature of fuel results in Americans paying for roughly 760 million gallons of gasoline and diesel fuel that they're not getting.

Additionally, because diesel fuel retailers are allowed to adjust for hot fuel temperature, and not required to adjust for cold fuel temperature, when paying road fuel taxes, and because retailers pay those taxes on the wholesale side, any amount of taxes a retailer subsequently collects above that total can be pocketed by the truck stop owner. State fuel tax collections, depending on state policies, might be affected differently but the 18.4 cent per gallon federal gasoline tax and the 24.4 cent per gallon federal diesel fuel tax is especially affected because of the way the IRS allows retailers to measure the fuel on which they pay taxes.

Every fuel tax dollar collected from truckers, and the public in general, needs to be used for the reason and purpose under which it's collected: maintaining and improving roads and highways.

Retrofitting Diesel Fuel Pumps - Cost

The state of Hawaii, during the fuel crisis of the '70s, mandatted that fuel sold in the Aloha state be metered at 234 cubic inches. Hawaiian lawmakers felt that the bigger Hawaiian gallon, which assumes a fuel temperature of 80 degrees, would be a temporary fix; in effect only until the U.S. required fuel pumps that adjusted the volume of gasoline and diesel delivered to the consumer to conform to the official standard.

Because they're still waiting; Hawaiian law still mandates a 234 cubic inch gallon.

So the question begs to be asked: "What would it cost to retrofit pumps with temperature adjusting metering devices?" The answer isn't conclusive because of the differences in pump types. Retrofit kits for electronic pumps, not including installation labor, are available at costs ranging from $650 to $2000 while the cost to retrofit mechanical pumps might be as high as $2700. Considering the number of fuel pumps dotting the country there's no doubt that the one time cost to retrofit every pump in the nation would be high: Somewhere north of one billion dollars but, probably, less than three billion dollars.

My suggestion would be to enact regulations that allowed diesel fuel retailers to upgrade their equipment over a period of 2-3 years and require oil companies and refineries, whose recent profits have been staggering, to participate in the cost.

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