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A study of seasonal effects on a low temperature Valve Train Wear (VTW) test has been carried out with the Nissan KA24E engine test. Initial tests in our laboratory with this engine with an in-house reference oil showed that VTW was more severe in the hot and humid Japanese summer compared to the very dry winter. This prompted a systematic study of VTW performance using a temperature and humidity controlled cell, this being carried out with a JASO reference oil and an in-house reference oil. This work clearly showed that cam nose height loss correlated linearly with absolute humidity, higher wear being measured under higher humidity conditions. The slope of this relationship varied with the lubricant, presumably reflecting the differing sensitivities of lubricant formulations to humidity-induced wear. A relationship was also found between VTW and sulphate ion content of used oils.