The introduction of this pressure switch introduces another potential problem. If this pressure switch fails, your engine will stop even if oil pressure is fine.

If you only sail your boat locally this is probably not a big issue. But if you cruise any distance from home it is one of the items you should have in your spares kit.

Suggested items for your engine spares kit:
• New water pump impeller
• Replacement belt
• This low pressure shutdown switch
• Spare fuel pump

Troubleshooting tip:
When starting the engine, the glow plug circuit overrides the low pressure shutdown function and provides power to the fuel pump momentarily. Once the engine starts and the oil pressure rises, the fuel pump completes the circuit for the fuel pump. If your engine starts and runs with the glow plug (warmup) switch engaged, but dies immediately on release of that switch, failure of the low oil pressure cutoff switch is the likely cause.

This switch is used on engines listed below (and the boats that we are aware used these engines... There could be other combinations as well):
• M-25XPB (Catalina 28 MkII, Catalina 30 MkIII, Catalina 310)
• M3-20B (Catalina 28 repower or others)
• M-35B (Catalina 34 MkII, Catalina 350, Catalina 36 MkII)
• W-42B (Catalina 400, original part number superseded by this part number)

Regardless if you are installing an oil pressure sender or an oil pressure switch, never add any type of Teflon tape or pipe joint compound on the threads. The sender or switch are modulating the connection of the instrument to ground by way of the engine block. If you insulate the threads, they can't make the connection to ground and the instrument will not function properly.