In my last post, I mentioned filling our fuel tank with 50 gallons of diesel fuel at the bargain price of $2.22/gallon on our way to Nashville. If you follow this blog, you probably have noticed that I often mention topping  up our tank with 40 or 50 gallons of fuel. We have a 100-gallon fuel tank, so why do I top off the tank so often? There are a number of reasons.

First of all, I’m the type of guy that likes to have at least a 1/4 tank of fuel in my vehicles at all times. You never know what may come up and stopping for fuel in an emergency situation – like driving someone to a hospital – doesn’t make sense to me. In our motorhome, a quarter tank of fuel isn’t enough. Our Onan 7.5kW Quiet Diesel generator draws fuel from the same tank that supplies our Cummins ISL diesel engine. The generator fuel pick-up is a stand pipe that extends approximately a quarter up into the tank. This means the generator can’t draw fuel if the tank is less than 1/4 full. This is by design – it prevents the operator from running the tank dry with the generator. That way when you dry camp, you’ll always have enough fuel in the tank to drive to a fuel station.

Another reason is moisture in the tank. Diesel fuel is hygroscopic. This means it will attract and hold moisture. The air space in the tank will have a certain amount of moisture in it, depending on temperature fluctuations and humidity. By keeping the tank full or nearly full of fuel, the air space is minimized and less moisture is present. Our main fuel filter is also a water separator. Water stays in the bottom of the filter where there’s a valve to periodically drain any water collected before it can get to the fuel injectors. I check ours from time to time, but I’ve never had a noticeable amount of water in the filter.

When I fill our tank, I treat the fuel with Biobor JF. When moisture is present in diesel fuel, microbial contamination can occur. There are hydrocarbon-utilizing microbes that thrive in the fuel/water interface. They live in the water and feed on the fuel. Biobor is an economical way to combat this. It also adds lubricity to the fuel. Since Ultra-Low Sulfur Diesel (ULSD) was mandated and and implemented at the end of 2010, diesel fuel doesn’t have the same lubricating properties it had before. ULSD has 15 ppm sulfur, previously it was 500 ppm. Fuel companies are supposed to blend lubricating additives in the fuel, but I like the peace of mind knowing that the Biobor adds lubricity.

Most of the time, I buy diesel fuel at a Pilot/Flying J travel center. I like knowing that I can pull into the trucker lane and have plenty of room to maneuver. I’ve read that most RV collision insurance claims occur in gas stations – people try to maneuver a large rig in a tight space and end up hitting something. I also like the high-speed nozzles at the trucker lane. I can pump 50 gallons in less than 5 minutes. I have a Pilot/Flying J RV Plus card that is a fuel credit card. I swipe the card at the pump – it automatically adjusts the price to seven cents below the advertised cash price and I can pump up to $1,000 of fuel. Most fuel stations will only allow $100 on a credit card. It’s a pain when you have the swipe your card, then go inside and give your card to the cashier to complete the fill-up.

Lately, I’ve been planning ahead for fuel stops. I have an app on my phone called TruckerPath that shows me all of the truck stops along my route. I also look at a web site called TruckMiles. This site shows daily average fuel prices by state. We’re in Tennessee now and will head to Memphis in a couple of days. We’ll probably overnight in West Memphis, Arkansas like we did on our way east. TruckMiles shows Tennessee diesel fuel prices average 10 cents/gallon less than Arkansas – so I should fill my tank before I leave Tennessee and enter Arkansas.

The last thing I look at when I plan my fuel stop is the Pilot/Flying J fuel price chart. I look at their prices and I also pay attention to the column showing the intended bio blend. Nowadays, a lot of diesel fuel is blended with bio-mass based fuel – it’s not all petroleum-based. Our generation (CAPS era) Cummins ISL engine is approved for up to 10% bio blend. The Pilot/Flying J chart shows the intended blend ( I think this is lawyer speak as they don’t guarantee the exact percentage). Bio blended fuel is noted with a “B” number – B5 is 5% bio, B10 is 10% bio and so on. Bio content in the fuel adds lubricity, but bio-mass based fuels are less stable than petroleum-based fuel. They also are more prone to attract and hold moisture. My preference is for B5 or less bio content. In some areas, such as Minnesota, it’s hard to find diesel fuel that’s less than B20. Again, by filling my tank when it’s half full, if I have to pump B20 into my tank, I’m cutting the percentage down by mixing it with the existing fuel in my tank.

That’s probably more than you ever wanted to know about filling up with diesel fuel. But if you read this far, it may help you decide where and what fuel to put in your tank.

We’ll head into town today, but first I need to get on the roof and reset my satellite antenna for the western arc satellites. I wrote about that here.