For decades, ENISO12205 test has been used to evaluate the long term storage stability of diesel fuels. Nowadays, new biocomponents especially FAME has increased the need to create faster and more appropriate test method to measure the long term storage stability. Developments in engine technology have also raised the need to create a new method to evaluate the thermal stability of diesel fuels. These new methods should have correlation to field experience. As an example it has been shown that Rancimat (EN15751) and PetroOXY EN16091 have a correlation when fuel contains more than 2% FAME. Rancimat is not applicable for FAME free fuels, so correlation based PetroOXY limit should be limited to fuels containing more than 2 vol% FAME.Study on oxidation stability test methods and their correlation to real life were continued and deepened (part 1: SAE 2013-01-2678). ENISO12205 and PetroOXY EN16091 test methods did not have a correlation according to the earlier studies. Also the tested fuels did not show any signs of oxidation or deterioration during the engine tests, where they were exposed to high temperature and pressure. For further studies, a range of different type of fuels was prepared to see how they differentiate in the stability test conditions. PetroOXY method was applied after the ENISO12205 test in order to evaluate if there is any stability reserve left in the fuels after being exposed to test temperature. Additionally, filterability characteristics of the fuels were studied after ENISO12205 test by using filter blocking tendency test (FBT, IP387). Fuel aging in PSA DW10 engine was studied by taking a sample from the fuel return flow before it entered back to the fuel tank. The fuel had been exposed to high pressure and temperature shortly without passing through a fuel filter after the exposure.