A muffler for an engine in oilfield applications has a tube with nozzles in its inlet section for spraying a mist of water from the well into the exhaust gases produced by the engine, so that a significant portion of the water is converted to water vapor and exits with the exhaust gases at the outlet of the tube. The methods and kits also allow prediction of disease outcome and staging of patients with regard to therapy. From the measured load on the drawbar, the lateral and longitudinal draft forces applied by the towed implement on the drawbar can be calculated.