How much gasoline contamination will significantly alter a lubrication regime?

In our oil analysis laboratory we tested the effect of gasoline contamination on the viscosity and flash point of a new lubricant and found repeatable results that can be helpful for refining industry clients. We injected gasoline at 0.5%, 1.0%, 2.0%, and 3.0% by weight into new lubricant samples to track the effect on oil viscosity at 40 degrees C (using ASTM D7279) and on flash point (using ASTM D6450, which is closed cup). By using this information our refining customers can estimate the level of gasoline contamination in used lubricants with spot testing of viscosity in-house.

Summary of Findings:

The oil analysis testing was performed on the same ISO VG 100 Group IV PAO, new and uncontaminated.

At 0.5% gasoline contamination the oil viscosity reduced by less than 5%, but the closed cup flash point of the lubricant sample reduced by more than 50%. At 1% gasoline contamination the reduction in viscosity was still less than 10%, which does not trigger a contamination alarm on most oil analysis lab reports. Although with only 1% contamination the flash point of oil reduced by 67%. At 2% gasoline contamination the viscosity reduced by approximately 20% which would be flagged as abnormally low by most oil analysis laboratories. And at 3% gasoline contamination the viscosity reduced by more than 50% and the flash point was lowered by 80% to approximately room temperature. It would require a cold room to track flash point accurately at greater than 3% gasoline contamination.

A few interesting take-aways: lubricant viscosity begins the very steep decline after 2% gasoline contamination. Closed cup flash point begins a steep decline at only 0.5% contamination. At >3% contamination the flash point approaches room temperature and can no longer correlate to the level of gasoline contamination unless testing is performed at well below room temperature.

August 13, 2020