Fluorohydrocarbon elastomers are well known for their resistance to heat and fluids. However, certain additive packages in lubricating oils have been found to have a deleterious effect on the properties of these rubbers. Consequently, a study was undertaken to determine the effect of oil additive on the properties of fluorohydrocarbon rubbers under total immersion conditions. Most of the tests were conducted at 163°C to accelerate the effects that might be observed under normal automotive operating temperatures. Performance was based on the change in elongation, degree of crazing and volume increase.