An engine head friction tester that has excellent repeatability, can differentiate between oils with good and poor friction properties and can also obtain steady sequential data for many hours has been developed. It was formerly thought that data variations were inevitable in this type of tester. However, analysis of specific factors of the variations showed that the main factors involved in the variation were the temperature gradient between the head and the torquemeter and the temperature change resulting from the aforementioned temperature gradient. Next, by almost completely separating the head side from the torquemeter side thermally and by taking measures to maintain both sides at their respective constant temperatures, along with other countermeasures, a tester having the special properties indicated above was developed. This paper describes some test results demonstrating the advantages listed above.