The coke formation and the kinematic viscosity at 100 ℃ of hydrogenated base oil and polyfluorene olefin (PAO) base oil,base oil containing different additives and engine oil were tested by using the crankcase coking performance tester,the viscosity change and coking tendency of additives and base oils under high temperature conditions were analyzed,and the test results were compared with the results of oven high temperature test.The test results show that among the three oil samples of 250N,20W-50 and PAO8,the coke of 250N base oil increases rapidly.The kinematic viscosity of pure base oils at 100 ℃ shows an upward trend,while kinematic viscosity of 20W-50 oil product is first decreased to a minimum of 15.8% and then increased.Zinc dialkyl dithiophosphate (T203) is the main source of coking in base oils containing additives,followed by viscosity index improvers,other additives have less influence on coking.The amount of coke of the PAO-based sample is significantly lower than the sample of 250N base oil.The purification effect of synthetic calcium sulfonate detergent on 250N base oil is better than that on PAO base oil.Viscosity index improver,compounding agent,polyisobutylene succinimide dispersant have a greater impact on the change of oil viscosity at 100 ℃.Oven high temperature static test shows that ethylenepropylene copolymer adhesive and phenolic antioxidant reduce the kinematic viscosity at 100 ℃ of the three oil samples after oil oven test.