You picked up a heavy load. You weighed yourself at a CAT Scale and made sure you're not over gross. You set your tandems so the weight is distributed within legal limits. Suppose you weighed yourself with only half fuel capacity. Do you know how much the weight of diesel fuel will affect your weight distribution?
Q. What's the weight of a gallon of diesel fuel?
About 7 pounds per gallon. It can vary depending on temperature, grade of diesel, biofuel additives, and other factors.
Water weighs 8.34 lbs per gallon. Liquids of different densities separate instead of mixing. The denser liquid tends to sink and the lighter liquid tends to float. That's why diesel fuel floats on top of the water in your truck's water separator.
Q. Does temperature affect the weight of diesel fuel?
Diesel fuel becomes denser at colder temperatures, less dense at warmer temperatures. This affects the weight slightly. In most weather conditions, a gallon of diesel weighs between 6.8 lbs and 7.1 lbs.
Q. What does a full tank of diesel fuel weigh?
It depends on your fuel capacity. If you have two 100-gallon fuel tanks, the fuel weight is about 1,400 lbs when the tanks are full. Most semi-trucks have a fuel capacity between 125 and 300 gallons.
Q. How should I calculate my fuel weight?
If you multiply the number of gallons of diesel fuel by 7, you'll get a pretty accurate fuel weight.
Building contractors add 10% to their calculations for budgeting, buying materials, and other things. It's better to err on the side of caution.
You'll be safe if you multiply by 7.1.
Read more about axle weight distribution in this axle weight distribution.
Q. Does #1 diesel fuel weigh more than #2 diesel?
#1 diesel is formulated for cold weather conditions. It's denser than #2 diesel so it weighs a little more. At 59ºF, number 1 diesel weighs about 7.3 lbs per gallon.
#2 diesel provides more power to the engine. It also has a higher viscosity than #1 diesel. The higher viscosity helps lubricate the seals, pistons, and injection pumps to reduce wear. But in cold temperatures #2 diesel thickens to a gel-like state. This stops the fuel flow and causes your engine to stall.
Winterized diesel sold in cold-weather areas contains a blend of #1 and #2 diesel.
Q. Does the biodiesel B5 blend weigh more?
Biodiesel B5 consists of 5% biodiesel and 95% petroleum diesel. That's the highest percentage of biodiesel you can use without voiding a manufacturer's warranty. B100, which is 100% biodiesel weighs 7.3 lbs per gallon at 59ºF.
7.3 X .05 = .365
7.0 X .95 = 6.65
.365 + 6.65 = 7.015
As you can see, B5 weighs slightly more. If you follow the building contractor's rule of adding 10% to your calculations, you won’t have any problem.
Q. What about AG diesel?
Also known as farm diesel, offroad diesel, and red diesel, AG diesel is not legal for highway use. It contains a red dye to distinguish it from highway diesel.
It's the same as highway diesel, except it's not taxed. That's why it's cheaper.
Don't use AG diesel on the highway — period. If you're pulled into a commercial vehicle weigh station for fuel inspection, the fines and penalties are hefty. This could be damaging to your trucking business.
You can find out more about highway use and fuel taxes here.
Q. Should I calculate diesel fuel weight differently when I fuel up in Canada?
Canadians use the metric system. You buy diesel fuel by the liter. If you go into a Canadian weigh station, they will measure your weight in kilograms rather than pounds.
- 1 gallon = 3.785 liters; 1 liter = .264 gallons
- 1 pound = 0.454 kilograms; 1 kilogram = 2.205 pounds
You should also know that axle weight distribution limits in Canada are measured in kilograms. Plus, the weight distribution limits are different than in the US:
- 5,500 kg steering axle (12,125 lbs; some provinces vary)
- 17,000 kg drive and tandem axles (37,479 lbs)
You can learn more about weight distribution in the US and Canada in this Owner-Operators Only blog post.
Q. Can't I just weigh with a full tank and be done with it?
The short answer: Yes. It's the best way to get the most accurate weight distribution.
The longer answer: It depends on your fuel optimization plan. If you can get a good price for fuel at the same truck stop where you scale your truck, wonderful. But if you know the price of fuel is better further down the road, it might be better to do the math.
Q. How is the weight of fuel distributed to the axles?
Most big trucks have fuel tanks beneath the sleeper berth. That's a short distance from the drive axles. Most of the fuel weight will go to the drive axles. It may have some bearing on the steer axle, but not much. The weight of diesel fuel has very little effect on the tandem axles.
Q. How can I set my tandem axles so that I don't go overweight on my axles?
If you can, set your tandem axles so that the drive axles have 31,000 lbs or less. That leaves you with 3,000 lbs to compensate for adding fuel. That's the weight of about 428 ¬Ω gallons of diesel fuel. Most big trucks have a fuel capacity of 300 gallons or less.
Here's more about how to set your tandem axles for weight distribution.
Conclusion
The weight of a gallon of diesel fuel is about 7 lbs. Temperature affects the density, so it's a little heavier in cold temps and lighter in warmer temps. In most weather conditions, a gallon of diesel weighs between 6.8 lbs and 7.1 lbs.
The easiest way to distribute axle weight is to scale your truck with the tanks full. But sometimes you can optimize your fuel costs better by purchasing fuel further down the road. That's when knowing how to calculate the weight of diesel fuel comes in handy.
It's better to err on the side of caution. You can get an accurate fuel weight by multiplying the number of gallons of diesel by 7. But if you multiply by 7.1, it gives you a safety cushion.
Biodiesel fuel is heavier than petroleum diesel. Biodiesel blends sold in the US are usually 5% biodiesel and 95% petroleum diesel. Using a blend of more than 5% bio will void a truck's warranty.
Winterized diesel contains a blend of #1 and #2 diesel. #2 diesel is the most efficient fuel for diesel engines, but it can gel in cold weather. Fuel vendors mix in #1 diesel in cold weather areas.
AG diesel is sold for offroad use. It' not taxed like highway diesel. It contains a red dye to identify it as AG diesel.
The weight of diesel fuel affects the weight of your drive axles more than the others. It may affect your steering axle somewhat. It has very little bearing on your tandem axles.
Related posts you might be interested in:
Truck Axle Weight on a 53' Trailer
An Owner-Operator's Guide to Taxes
IFTA Stickers and IFTA Reporting