Fuel Temperature

[TerryM]

I recently installed the SilverLeaf system on a tablet computer and we are just back from our first trip with it. One of the gauges is fuel temperature. Last week when we are running from Cincinnati to western NY the ambient temperature was in the high 80's, fuel tank started full and ran down to half and fuel temperature was around 133 degrees. I have never given any thought to fuel temperature so I wasn't sure what to do with the information.

Today ambient temperature was 97 degrees, fuel was half to quarter tank and fuel temperature climbed from 133 most of the day to 144 degrees this afternoon.

Fuel temperature of 144 degrees sounds hot. Should I be concerned? Should I have done something?

Thanks in advance for any input.

Terry

[Jon Wehrenberg]

On our engines excess fuel is returned to the fuel tank. That fuel picks up heat as it makes its journey from the tank, through the pump and engine and back to the tank. While you may see that as worrisome it is actually good news. If you are driving on a sub zero day you may see a lot of semis along the rad with gelled fuel. They have the same situation, but their fuel lines and tanks are much more exposed so the fuel stops flowing.

On your coach the tanks are sandwiched between two bays and the only part of the tanks exposed is the bottom. As a result that warm return fuel will keep your fuel tanks warm (relatively speaking) and you will not have an issue with gelling.

Did you notice your fuel temps tracked the ambient temp?

[travelite]

The fuel also cools the injectors.

[AmeriStar]

Fuel temperatures of 130 f to 150 f for diesel is quite common to see on hot days. Althought the flash point of diesel is within this range, don't worry, the autoignition temperature is above 400 f.

Hot temps do have an affect on the 'amount of fuel' you purchase at the pump. Try to purchase your fuel early in the day when traveling thru hot areas. 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 (approx 145,000 btu). At 90 degrees, however, the same amount of diesel fuel expands to more than 235 cubic inches; but pumps are still set to deliver the standard 231 cubic inches.
Every degree, over and above the 60 degree standard, diminishes the energy contained in a 231-cubic-inch gallon.

[GDeen]

Fuel temperatures of 130 f to 150 f for diesel is quite common to see on hot days. Althought the flash point of diesel is within this range, don't worry, the autoignition temperature is above 400 f.

Hot temps do have an affect on the 'amount of fuel' you purchase at the pump. Try to purchase your fuel early in the day when traveling thru hot areas. 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 (approx 145,000 btu). At 90 degrees, however, the same amount of diesel fuel expands to more than 235 cubic inches; but pumps are still set to deliver the standard 231 cubic inches.
Every degree, over and above the 60 degree standard, diminishes the energy contained in a 231-cubic-inch gallon.

Practically, I wonder how much ambient temps in a given day effect fuel being delivered at a high rate from an underground tank. Maybe the first few gallons are warmer, but my bet is the average temp of the fuel passing through the meter is the same at 6 AM as it is at 3 PM. Do you guys have data to show otherwise?

[TerryM]

I guessed the increase in fuel temp was caused by an increase in ambient temp and a decrease in fuel level. My logic was - less fuel so it recirculates quicker and therefore does not have time to cool. Then I thought - millions of Prevost miles driven in all kinds of weather - I was probably over-thinking the situation and I should just drive.

Thanks for the help.

Terry

[travelite]

It really is another coolant for the engine, it pulls heat out of the fuel rack and keeps injectors and other vital parts at their proper operating temps. This is another reason not to let the fuel level in the tank get too low. Prevost even has a fuel cooler mounted on the outside of the radiator stack. It's a small radiator about 8"x10" - solely for the purpose of getting cool fuel into the fuel rack to sink heat.

[Jon Wehrenberg]

I don't know if this is true or not, but David's point about fuel being used for cooling is probably a critical function. The new engines, due to emissions requirements are running even hotter than the 8V92 and the Series 60 engines most of us run. This makes coolant, oil (also used for cooling), and fuel system condition critical.

Since almost all engine parameters are being monitored, if the fuel temperature on your coach were an issue it is likely you would get a CEL and have a code.

[AmeriStar]

Gordon,
Actually there have been quite a few instances where fuel is delivered at a higher temperature. In most of the newer truckstops, fuel is not stored below ground any longer, but is stored above ground as a precation in case of leaks that could enter the ground water.