Abstract: A method for heating flowing back wellbore fluids or heating fluids to treat wellbores or pipelines having a tubing string is disclosed. The wellbore will intersect a hydrocarbon reservoir. The method will include providing a diesel engine that produces heat as a result of its operation. The engine will in turn produce a gas exhaust, a water exhaust, and a hydraulic oil exhaust. The method would further include channeling the exhaust to a series of heat exchangers. The method may further include flowing a wellbore fluid into the heat exchangers and heating the wellbore fluid in the series of heat exchangers by heat transfer from the exhaust to the wellbore fluid.