Propylene glycol (PG) is gaining in popularity as an engine coolant in market areas concerned about the toxicity of ethylene glycol (EG). With the possibility of PG coolants being used in heavy duty diesel engines, the requirement to control cylinder liner cavitation must be maintained. The purpose of this test program was to compare the ability of propylene glycol and ethylene glycol based heavy duty engine coolants to suppress cavitation of wet-cylinder liners in heavy duty diesel engines.The first task was to develop an engine test that would duplicate liner cavitation in a short time. This was accomplished with a 250 hour accelerated cycle test of a modified Deere six cylinder, 10.1 liter engine. The next step was to establish a baseline with both PG and EG using a modified GM 6038 engine coolant mixed 50 percent by volume with American Society of Testing and Materials (ASTM) standard corrosive water. This was followed by tests using coolants with the same formulation containing a full charge of a generic supplemental coolant additive (SCA). Five runs were made in this test program.This study demonstrated that PG and EG based coolants are essentially equivalent in their ability to suppress cylinder liner cavitation in diesel engines; and, the addition of a suitable heavy duty engine SCA to both types of coolant is equally effective in reducing cavitation sensitivity. This test program also demonstrated a poor correlation between the proposed ASTM Ultrasonic Bench Test and engine tests.