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1978 - 150 HP Mercury Outboard - PSI Reading

A

aquaholictom

New member
I have a 1978 - 150 HP Outboard on a 22 ft center console that I just bought. On the console it has a gauge that measures PSI. I traced the wire back to the engine and it appears its going into the exhaust manifold.
My question is what is it measuring and why?
 
Safe bet it's measuring water pressure in the cooling system.

At idle you should be getting maybe 3 or 4 psi and above 5000 rpms, 12 psi (minimum) would be in order on a properly functioning cooling system.

This would be a better indicator of "when" the waterpump needs servicing than a straight temp gauge which may not sound the alarm until the system is pretty much shot...
 
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