As part of a client’s preventive maintenance program, MRT performed routine oil analysis on critical rotating equipment. MRT repeatedly identified coolant contaminating the lubricant in a compressor lube oil system. A pressure test on the unit heat exchangers did not indicate a coolant leak. Still the water level in the lube oil system continued to increase. Finally, a pressure test was completed while the unit was still hot from operation rather than after it had cooled down. Sure enough, there was a crack in the coolant tube sheet that was opening when the bundle was heated to normal operating temperature and resealing when it cooled. The takeaway message: the client trusted the oil analysis and continued to investigate the source of water contamination until it was found.