Mercury - Oil Pressure Sender, 80 PSI Instrumentation 815425. Overview. On a MerCruiser, the oil pressure sender is one of those small parts that can make the whole engine seem like it's acting up when really the sender's just tired. A bad one will have your gauge flickering, dropping to zero, or giving readings that don't match what the engine sounds like. Swapping in this OEM sender brings the gauge back to giving steady, believable numbers so you're not guessing whether you actually have a pr