In the present study, it was aimed to evaluate heat balance numerically and experimentally in various diesel engines for neat diesel fuel (NDF) and gasoline fumigation (GF). From various numerical applications, it is determined that Useful work increases for GF. Combustion duration increases with increasing GF and thus heat transfer to the walls increases. As exhaust temperature increases, exhaust losses also increase for GF. In the experimental study, heat balance analysis for NDF and GF has been performed in a single cylinder test engine. Heat lost through the exhaust decreases until 4-6% GF ratios and at higher fumigation ratios it starts to increase because of increasing exhaust gas temperature. Heat rejected to the cooling water decreases at low fumigation ratios, but at high fumigation ratios it increases. Other losses generally exhibit an increasing tendency at low fumigation ratios.