Emissions from diesel engines have become an important problem today due to their positive effects on global-warming. There are strict restrictions on emissions and low emission diesel engines are required to be developed. Particularly, exhaust thermal management systems are really important for diesel engines to reduce the emissions. However; for diesel engines, at low speed and low load conditions, exhaust gas temperatures are not generally higher than 250 degrees C. That not only leads to inefficient after-treatment systems but also insufficient emission reduction. Variable Valve Timing (VVT) can be used to achieve those high exhaust gas temperatures by changing the opening and closing timings of the exhaust valves at any speed and any load. Thus, the aim of this study is to try to increase the exhaust gas temperature of a diesel engine above 250 degrees C whenever necessary by changing the exhaust valve opening and closing timings for various engine speed and load conditions. The process is also applied for areas which already have temperatures greater than 250 degrees C. Diesel engine system is simulated by using Lotus Engine Simulation (LES) program. It is then validated with experimental results. It is seen that exhaust gas temperatures can be raised higher than 250 degrees C for most of the loading cases when exhaust valve timings are changed. But there is also bsfc growth in the system which needs to be considered.