The sealing of diesel engine crankshafts -a comparison of PTFE and fluorpolymerRadial lip seals have been successfully used for decades for the sealing of crankshafts. Since the introduction of fluorpolymers most demands have been mastered. Several factors - less oil-changes, turbocharging and higher truck engine performance - have led to disturbance of the sealing process arising from the deposition of oil residues in the sealing gap. Knowing the reasons for this disturbance, namely the high specific thermal demand placed upon the medium in the sealing gap, helps in finding preventative measures. A seal with hydrodynamic sealing aids in conjunction with a sliding element based on PTFE which has a low coefficient of friction reduces considerably the specific thermal demand. Both sealing systems are compared on the basis of test results and indications made of the questions remaining to be answered.