Originally Posted by JohnFitz
Generally speaking diesels need some reserve fuel in the tank for cooling. The engine fuel pump pulls in much more than it burns and sends a lot of fuel back to the tank in a return line. The engine uses the fuel for cooling the injector pump and on many engines the ECM. If too little fuel is left in the tank the recycling fuel will get too hot and the injector pump will have increased wear. It could be that CC placed the pickup line at the 20% full mark for this reason. But the gauge should still read E at this level. I've seen specs listing both tank size and "usable" capacity but usually I just see tank size.
Another reason to keep the fuel cool is efficiency: every 10 degrees F increase reduces the efficiency by about 1%- nothing that would normally be noticed on the road.
Just wondering if you have seen any manufactures recommend keeping a certian amount of fuel in a tank for cooling purposes.
I have been involved in diesel powered equipment my whole career and never heard of that.
The last 16 years I managed a facility where it was routine to refuel much of the equipment when the low ( near empty )fuel light came on.
We would replace the machines at around 20,000 hours and still have the original fuel system components with the exception of some lift pumps.
Running the tanks low also helped eliminate the sludge build up, by sloshing the fuel around.
We ran Cat, Cummins, Mack, Duitz, JD and an assortment of other diesel engines.