We had this issue back in the winter. We found that the drivers were running the lines out of propane at the end of the shift. they would turn off the tank and run the engine full throttle.........or sometimes the propane companys might overfill the tank, when they opened the tank it was to much pressure. We have advised to turn the tanks on/off slowly and don't run the engine at full throttle to drain the lines........so far no problems......knock on wood. Hope this helps