Experimental Investigation on the Impact of Engine Oil on RTV Silicone

Silicone-based RTV sealants see widespread use in the automotive industry. In the uncured state, RTV silicone has the consistency of thick toothpaste and can be easily applied to form an effective seal. However, a significant amount of anecdotal evidence suggests issues exist with RTV’s ability to maintain a satisfactory seal in some long-term engine sealing applications. ASTM D7216 is used to evaluate the effects of different oil blends on a set of standard molded reference samples after submersion in an elevated temperature oil bath. The evaluated material properties are hardness, percent volume change, tensile strength, and ultimate elongation. A library of such results is readily available through Savant Laboratories of Midland, Michigan. Given RTV’s widespread use, surprisingly no such library of information exists concerning an engine oil’s effects on different RTVs. Due to difficulties in obtaining the reference oil, a commercially available engine oil was selected as a reference and RTV specimens were evaluated against the ASTM D7216 reference silicone (VMQ) for comparison. Both the hardness of the RTV and VMQ decreased by ~30%, though the final hardness of VMQ is approximately 3 that of RTV. Volume change of both materials increased on the order of 20%. Tensile strength of the RTV appeared unchanged after conditioning, while VMQ experienced a 40% decrease. However, after conditioning the tensile strength of VMQ still remained 3× that of RTV. Ultimate elongation of the RTV appeared unchanged while VMQ decreased by 23%. The conditioned ultimate elongation of VMQ remained on par with conditioned RTV. While both the RTV and VMQ samples are silicone based, significant differences in the changes to their material properties exist when exposed to engine oil at an elevated temperature. This may preclude a direct interchange in their usage and require re-engineering to produce a robust sealing system.