The COMBUSTION LEAK TEST is for CO (carbon monoxide) content in the coolong system, if the liquid used in this test changes color, you still have an internal engine problem. No doubt about it if this test is done right! If it is overheating at road speed (55mph) for say 5 miles, then cooling fans really dont come into play, however if overheating sitting still or slower speeds, fans may be a problem. Was it doing the 'same' thing before the work you did??